Building Pathology

Question 1

During a defects inspection spalled bricks are identified. What are the common causes?

Answer 1

• Use of incorrect mortar on historic buildings – modern cement mortars, rather than lime.
• Moisture in the brick during a freeze thaw cycle
• Rainwater hitting the surface, poor drainage or water consistently running down the brick.
• Non-breathable coatings such as sealants – unable to dispel water through its pores.
• High pressure cleaning

Question 2

What problems are associated with vegetation growth to damp/shaded brickwork?

Answer 2

• They cause erosion of the mortar joints, hold and attract moisture, storing it within the brickwork, causing problems of water penetration.

Question 3

What is meant by the term concrete cancer?

Answer 3

• Alkali Silica Reaction (ASR), the most common form of alkali-aggregate reaction (AAR)

Question 4

What is ASR?

Answer 4

• It occurs when, given the correct combination of conditions, the highly alkaline pore water can react with certain types of aggregate to produce gel. It needs critical silica in the aggregate, sufficient moisture and high alkalinity from the cement or other sources to occur.
• The gel absorbs water to expand and can cause the concrete to crack or disrupt, including map cracking and small pop outs. A white gel can also be seen oozing out of the concrete.
• The durability of the concrete can be compromised and in some cases the tensile strength of the concrete component can be reduced. It is very damaging, sometimes resulting in structural failure and the need to demolish a building.
• Infrequent in the UK since the introduction of BS 8500 – British standard for concrete.

Question 5

Explain carbonation.

Answer 5

• It is the reaction of atmospheric carbon dioxide with the calcium hydroxide within the cement mix. The reaction produces calcium carbonate and lowers the PH to around 9 (from 12). This reduction starts on the surface, but can ultimately reach the depth of the steel reinforcement via capillary action. If the alkalinity reduces the passive resistive layer to the surface of the steel reinforcement, it will start to corrode and expand, causing cracking and spalling to the concrete. This allows further water ingress, accelerating the deterioration of the concrete. Particularly an issue if the reinforcement has insufficient concrete cover. The quality of the concrete will also have an effect, as the more porous the concrete, the quicker the process will occur.

Question 6

How does sulphate attack affect concrete?

Answer 6

How does sulphate attack affect concrete?

• Sulphates/ salts of e.g gypsum are water soluble and are readily transported into the cement mortar/concrete where they react with the tricalcium aluminate in cement to form crystals, generating high expansive forces in the mortar/concrete.
• To occur there must be sufficient sulphate and sufficient long term water.

Question 7

What are the key indicators of cavity wall tie failure?

Answer 7

• Horizontal cracking along the mortar joint the ties are embedded in, occurring at regular intervals (5/6 and 7/8 courses) with displacement of adjacent bricks.
• May also be stepped cracking where mortar joints are thin and hard.
• Corroding tiles expand so the bed joints widen and the outer leaf grows in height, which causes the outer leaf to bow (deflect). Also leads to gaps around windows.
• Can lead to pagoda effect at exposed gables.
• Vertical cracks may be evident external/internal wall junctions and horizontal cracks appear at junctions of wall and ceiling.
• Exposed elevations within industrial and marine environments are more prone, especially where exposed to driving rain and salt laden air.
• Inadequate protection of ties prior to 1930, often left untreated. Substandard galvanising between 1964-1981.

Question 8

How can stonework be repaired?

Answer 8

• Minor repointing of eroded joints (lime or earth based mortar)
• Rebedding loose stones
• Filling of cavities by a skilled mason using coloured mortar, reinforced with non-ferrous armatures for deeper patches.
• De-frassing to lightly brush off loose material
• Stones can sometimes be removed and reversed to hide the deterioration.
• Fractured or delaminating stone might be grouted and pinned.
• Only stones that are severely defective and be unable to fulfil their structural or weathering function should be replaced.

Question 9

How would you rectify the issue of wall tie failure?

Answer 9

• Cast and wrought iron wall ties (1850-1920) sometimes protected by bitumen – tend to snap, rather than corrode and a significant number need to fail before serious collapse is imminent.
• 1970s – galvanised wire ‘butterfly’ wall ties had too thin coating of zinc and are particularly prone to failure.
• Principle remedy to remove the old wall ties and either stitch in new or drill in new ones and fix them with resin or expanding anchors.
• Products such as Helix spiral replacement wall ties and Triton wall tiles are used.
• Type of remedy and tie must be matched to the type of failure that has occurred.
• If the wall has failed due to expansion of the tie within the brickwork, or if both leaves are cracked, a structural engineer may have to be consulted to assess the best remedial action.
• Refer to BRE Digest 329.
• Locate ties with a metal detector
• Remove, crop or encapsulate existing/failed wall ties.
• New ties can be fixed by:
  o Resin fix
  o Mechanical fix
  o Cementitious wall anchors
• Holes are drilled, ties installed and tightened to required torque,
• Cracked brickwork and mortar can be replaced.

Question 10

A white powdery substance has appeared on the surface of some new brickwork. What might it be and what can you do about it?

Answer 10

• Soluble salt crystallisation – unsightly efflorescence on the surface.
• Can lead to delaminating brickwork
• Common in new brickwork
• Recurrent efflorescence is common with faulty detailing.
• Salts can be contained in the bricks or surrounding atmosphere
• The salt solution passes through the pores or dry material and leaves a deposit within the pores upon evaporation.
• Deposited salts accumulate at depth of wetting and create back pressure which delaminates the brick – this exposes pores behind and the process is repeated.
• If left, it will progress as frost attack causing delamination and friable bricks.
• Clean off the efflorescence with a stiff bristled brush followed by a wet sponging with a mild solution.
• If it persists remove the source of wetting and replace bricks if appropriate.

Question 11

The reinforcement bars on a concrete building are exposed and corroding. What are the causes and remedial work strategies?

Answer 11

• Carbonation – occurs due to ingress of atmospheric carbon dioxide reacting with water within the concrete, which forms carbonic acid that neutralises the concrete’s alkalinity. This breaks down the passive layer around the reinforcement causing it to corrode due to the presence of water and oxygen at a slowly progressing rate. It s more of a concern when there is poor cover over the steel reinforcement or the concrete is poorly compacted. It is more rapid in porous concrete with low cement content and concrete with a high water: cement ratio. It can lead to a loss of strength and in extreme cases structural failure.
• Chloride attack – calcium chloride may be present in reinforced concrete as a result of its inclusion as an accelerator, by contamination from de-icing salts or from the use of unwashed or poorly washed marine aggregates. Sufficient levels of chloride may result in chloride induced corrosion, which can be more difficult to deal with than corrosion caused purely by carbonation. Its effects can be wide ranging, including a reduction in structural capacity. Passive film forms on steel and remains intact providing concrete remains highly alkaline (12.6+ PH). Use of calcium chloride accelerators popular in 50s and 60, but was banned in 1977. Corrosion may occur in concrete that contains sufficient chlorides, even if its not carbonated or showing visible signs of deterioration. Free chloride ions and combined chloride ions in concrete – free chloride ions within pore structure of concrete interferes with passive protective film on steel. Chloride induced corrosion in localised breakdown of passive film, rather than widespread deterioration that occurs with carbonation. Result is rapid corrosion of metal at anode, leading to formation of a pit in the bar surface and significant loss of cross-sectional area (pitting corrosion). Occasionally the bar may be completely eaten through, but can occur without any visual sign of cracking/spalling. Exaggerated by presence of deep carbonation – additional free chloride ions increases likelihood of corrosion.
• ASR (concrete cancer) occurs when pore water reacts with certain aggregates to produce a gel, which absorbs water, expands and causes cracking. 3 factors must be present – critical silica in the aggregate (troublesome aggregates in the SW), sufficient moisture, high alkalinity from cement/external sources. Can result in structural failure and need to demolish building if tensile strength of concrete is reduced.
• Repairs include:
  o Carbonation:
   Removing defective concrete and cut out the reinforcement to damaged members. New reinforcement fixed butt-welding to existing and new concrete cast.
   Guniting – (proprietary process) fine concrete sprayed to concrete surface under repair at high velocity.
   Coating/sealants/membranes can reduce carbonation progress, but if chlorides are present as rebar depth coating will not prevent carbonation.
   Electrochemical re-alkalinisation – cathodic reactions around rebar produce hydroxyl ions
  • steel cathodes attract alkali metal ions towards its surface, so high alkalinity is restored around rebar.
  • Temporary anode (steel mesh) attached to concrete. The electrolyte penetrates concrete and raises alkalinity at cover. Anti-carbonation coating then applied.
   Cathodic protection – permanent and very expensive technique. Anode system (coating or mesh) sprayed/fixed to whole surface of concrete. Current applied which passes to reinforcement, which is then made cathode, preventing corrosion of reinforcement.
  o Calcium chloride:
   Assess extent of chloride by sampling/testing and assess extent of corrosion and depth of rebar.
   Either shore up or demolish if building structurally affected.
   Difficult to repair as new corrosion cells forms on boundary of repair – use of zinc anodes embedded in repair and attached to rebar can reduce effect.
   Cathodic protection available for high levels of chlorides.
   Could apply corrosion inhibitors to surface.
  o ASR
   Replacing spalled concrete and reinforcement often the most suitable repair. Remove spalled concrete and corroded rebar and replace. Clean and treat surrounding areas, and repair using cement mortar, epoxy mortar or concrete.

Question 12

What tests are available to detect carbonation?

Answer 12

• The extent and depth can be confirmed using manganese hydroxide or phenolpthalin solution.
• Phenolpthalin indicator – phenolpthalin solution reacts with uncarbonated cement by leaving a pink indicator.
• Electromagnetic device can detect reinforcement positions, cover depths and diameters.
• Samples can be sent to a lab for testing.

Question 13

How would you specify repairs to concrete affected by carbonation?

Answer 13

o Removing defective concrete and cut out the reinforcement to damaged members. New reinforcement fixed butt-welding to existing and new concrete cast.
o Guniting – (proprietary process) fine concrete sprayed to concrete surface under repair at high velocity.
o Coating/sealants/membranes can reduce carbonation progress, but if chlorides are present as rebar depth coating will not prevent carbonation.
o Electrochemical re-alkalinisation – cathodic reactions around rebar produce hydroxyl ions
 – steel cathodes attract alkali metal ions towards its surface, so high alkalinity is restored around rebar.
 Temporary anode (steel mesh) attached to concrete. The electrolyte penetrates concrete and raises alkalinity at cover. Anti-carbonation coating then applied.
o Cathodic protection – permanent and very expensive technique. Anode system (coating or mesh) sprayed/fixed to whole surface of concrete. Current applied which passes to reinforcement, which is then made cathode, preventing corrosion of reinforcement.

Question 14

Explain how you would deal with a case of sulphate attack on concrete

Answer 14

• Must be high levels of water-soluble sulphates within the adjacent ground. To affect concrete buried in the ground, concrete must be of low density and must be a large amount of moisture movement through the concrete. Common cause is contaminated hardcore beneath concrete floor slab – sulphates become mobile due to a broken drain/high water table. Sulphate enters concrete (solution form), water evaporates leaving the sulphates, they react with calcium hydroxide and calcium aluminates causing expansion and the concrete deteriorates – cracking and heave.
• Concrete should be removed along with contaminated hardcore.

Question 15

Explain how you would deal with a case of ASR.

Answer 15

• Occurs when pore water reacts with certain aggregates to produce a gel, which absorbs water, expands and causes cracking. 3 factors must be present – critical silica in the aggregate (troublesome aggregates in the SW), sufficient moisture, high alkalinity from cement/external sources. Can result in structural failure and need to demolish building if tensile strength of concrete is reduced.
• Repair by replacing spalled concrete and reinforcement often the most suitable repair. Remove spalled concrete and corroded rebar and replace. Clean and treat surrounding areas, and repair using cement mortar, epoxy mortar or concrete.

Question 16

Can you list some common defects which occur in masonry?

Answer 16

• Cavity wall tie corrosion
• Lack of movement joints
• Frost attack
• Soluble salt crystallisation (efflorescence)
• Calcium silicate brickwork

Question 17

What are the signs of cavity wall tie failure?

Answer 17

• Horizontal cracking to mortar joints at regular intervals
• Expansion of the outer leaf of brickwork
• Wall bulges at 900mm horizontally and 450mm vertically.

Question 18

What causes cavity wall tie failure?

Answer 18

• Corrosion of the ties due to poorly galvanised ties between 1960s and early 1980s
• Corrosion of embedded tie in black ash mortar due to chemical action (sulphates)
• Wall ties may have been incorrectly or be insufficient in number

Question 19

What are the ways in which wall tie corrosion can be remedied?

Answer 19

• Resin fixed
• Mechanically fixed
• Cementitious wall anchors

Question 20

How are cementitious wall anchors installed to a cavity wall?

Answer 20

• Holes are drilled, ties installed and tightened to the required torque.
• Cracked brickwork and mortar can be replaced.

Question 21

Where would you expect to find movement joints in masonry and how frequently should they be installed?

Answer 21

• In long stretches of masonry, such as terraced houses
• Boundary walls
• Should be placed every 12-15m

Question 22

What are the issues that are caused without having movement joints?

Answer 22

• Thermal movement occurs in the brickwork
• The book end effect takes place
• Movement results from the expansion of the brickwork due to a rise of moisture content

Question 23

How would you remedy defects caused by a lack of expansion joints in masonry walls?

Answer 23

• Cur new 16mm movement joints every 12-15m in the brickwork.

Question 24

What is frost attack and how would you recognise it and where does it take place in masonry walls?

Answer 24

• It is the spalling of brickwork owing to the effects of water ingress, which can lead to the total disintegration of the brickwork.
• It takes place to exposed brickwork such as a parapet wall or exposed elevations.

Question 25

How is frost attack caused in a brickwork wall?

Answer 25

- It can occur in older bricks and those under burnt during firing - It occurs near the surface of the bricks as moisture gains easy access - Frost attack then takes place which requires regular freeze and thaw cycles when the material is wet. The expansion caused by the freezing of the trapped water causes the brick to break/spall off.

Question 26

How would you remedy sections of spalled brickwork?

Answer 26

- Remove the source of wetting i.e. repair leaking rainwater goods etc - Cut out and replace the defective sections of brick in isolated locations

Question 27

What is soluble crystallisation and how is it caused?

Answer 27

- Unsightly salt deposits, efflorescence, are deposited on the surface of the brickwork and display white staining - It is caused by salts contained within the brickwork passing through the pores of dry material and leave the salts on the surface upon evaporation - Deposited salts gather at the depth of wetting and create back pressure which delaminates the brick - This exposes pores and the process repeats

Question 28

What are the issues with calcium silicate brickwork?

Answer 28

- Unrestrained thermal expansion takes place - There is generally poor resistance to frost when brickwork is contaminated by chloride due to sea water (not used near coast) - Diagonal cracking often takes place which then allows moisture ingress to occur.

Question 29

What are the remedial measures available for defects due to calcium silicate brickwork?

Answer 29

- Re-point in a sulphate resisting mortar if ground water contains sulphate - Allow for adequate movement joints at 12-15m centres.

Question 30

How might you identify that calcium chloride has affected a concrete structure?

Answer 30

- Corrosion of the steel reinforcement has taken place and caused the concrete to spall off. - Visible rust staining to the steel reinforcement.

Question 31

What causes concrete to suffer from calcium chloride?

Answer 31

- Calcium chloride was used as an accelerator for setting concrete in the 1950s and 60s. - De-icing salts can also be a problem in concrete car parks - When chlorides are present in the concrete, the steel reinforcement corrodes when through it is in an alkaline environment.

Question 32

Can you tell me how you would know that calcium chloride was the cause of the corrosion to concrete and subsequent delamination of the cover rather than carbonation?

Answer 32

- Unlike carbonation, calcium chloride corrosion is localised and is known as pitting. - If left, the steel reinforcement can completely be destroyed by the corrosion which is darker in colour than corrosion by carbonation.

Question 33

Can you tell me some factors that might affect the resistance of concrete to chloride penetration?

Answer 33

- Depth of the concrete cover - Mix design - Use of admixtures - Degree of curing

Question 34

What remedial repair options would you advise your client to take when dealing with a building suffering from calcium chloride?

Answer 34

- In the first instance, assessment of the extent of the chloride should be undertaken by sampling and chemical testing. - Assess the depth of the rebar and extent of corrosion - Then take appropriate action, such as shoring or, in extreme cases, demolition. - Use of zinc anodes embedded in a repair and attached to the rebar can reduce the effect of the calcium chloride, but it is not a permanent cure. - Cathodic protection can be used but it is expensive and complex

Question 35

What is ASR and how might you identify it on site?

Answer 35

- Alkali Silica Reaction produces a map pattern cracking effect with small concrete pop outs. - Uncommon to building structures and is seen more in civil structures.

Question 36

What causes ASR?

Answer 36

- It occurs when water in the concrete pores reacts with certain aggregates to create a gel. - The gel absorbs water, expands and causes the concrete to crack - For ASR to occur it is depended on 3 factors – 1. Silica in the aggregate 2. Sufficient moisture 3. High alkalinity.

Question 37

What is the difference between AAR and ASR?

Answer 37

- Alkali Aggregate Reaction is the main concrete deterioration risk associated with aggregates, but ASR is the most common form of AAR.

Question 38

How do you remedy ASR?

Answer 38

- Take a risk based approach i.e. is the consequence severe, such as failure of the structure? - Replacing a reinforcement and the spalled section of concrete is often the most suitable, relatively short term repair.

Question 39

What is plastic cracking in concrete?

Answer 39

- Segregation or obstructions within the concrete i.e. reinforcement spaces. - The concrete is normally horizontal and may combine to honeycomb effect. - Result of rapid drying out of the concrete

Question 40

Can you name some typical stone defects?

Answer 40

- Pollution - Thermal stress - Wearing by wind borne solids

Question 41

How does pollution cause damage to stonework?

Answer 41

- Sulphur dioxide and water can make the surface of stones rough and cause surface crazing - In coastal areas the wind can carry and deposit sea spray on the stones which will deposit chlorides on the stone’s surface.

Question 42

How is thermal stress caused to stonework?

Answer 42

- The day time sun warms the surface of the stonework and at night this is reversed causing differential thermal stress and fatigue of material. - The wetting depth of the material/susceptibility to water ingress becomes greater.

Question 43

How does wearing by wind borne solids affect stonework?

Answer 43

- In coastal areas some solids, such as sand grains, may be carried considerable distances by strong winds, which will slowly erode the surface of the stonework - This will affect the stone’s ability to resist the passage of moisture.

Question 44

What are the typical defects associated with a 1960s high rise office block?

Answer 44

- Condensation - Failure of external cladding and structural components - Deteriorated DPCs - Floor slab settlement - Lack of a DPM - Deteriorated plastic plumbing goods - Brittle sarking felt - Rotted softwood timbers - Failing flat roofs - Wall tie corrosion - Spalling concrete - Corrosion of metal frames. - Deleterious materials – HAC, asbestos, woodwool slabs, concrete carbonation, calcium chloride accelerators, corrosion of reinforcement and metal structures (fire escape), fixing failure (external wall panels, parapet walls). - Low performance for dampness and insulation.

Question 45

Your client has just bought a concrete framed office block, built in the 1960s. Explain to him the issues that will need to be considered when refurbishing the building from a pathology point of view.

Answer 45

- Whether HAC, hollow clay pot or wood wool slabs were used in the construction of the property. - Whether the concrete frame suffers from carbonation, chloride attack, ASR or sulphate attack and will require remedial works. - There may be low floor loading which may not accommodate current loads without strengthening. - The building may be poorly insulated with high air infiltration rates.

Question 46

Your client has a concrete clad building that is suffering from carbonation. You have repaired the current defective areas. How can you prevent further problems occurring?

Answer 46

- You can treat the surface of the concrete to stop the concrete alkalining, but must be crack proof coatings to be effective. - Alternatively could install cathodic protection, but this is expensive.

Question 47

Your client’s building is known to have been built using HAC concrete. Is this a problem? What would you recommend that he does about it?

Answer 47

- Often there are no implications if left, but it would depend on situations and conditions. Most structures have sufficient reserve strength even when converted. - In order to ensure that there are no issues, I would recommend that my client undertakes an investigation consisting of sample testing to assess the HAC’s strength, extent of conversion, and durability, determining what materials were used from the Local Authorities’ records of HAC buildings. - If the strength has been reduced, the live loads will either need to be reduced or strengthening will be required. - Localised repairs of any reinforcement corrosion.

Question 48

Can you tell me some typical defects to a 1960s concrete portal frame building?

Answer 48

- Leak to asbestos cement roof sheets - Carbonation to the concrete frame - Cavity wall tie failure - Cracking and delamination to the ground bearing slab.

Question 49

What was the primary type of asbestos used in asbestos cement roof sheets and how long should they last for?

Answer 49

- Chrysotile | - Between 40-60 years

Question 50

How might you identify if the asbestos cement roof sheets are leaking/defective?

Answer 50

- Cracking parallel with the long edge - Cracking across the width of the sheet - Corrosion of the fixings - Moss growth and surface deterioration

Question 51

How are the cracks to the width of the sheet caused?

Answer 51

- Structural movement - Overloading/foot traffic - Wind loads coupled with defective fixings

Question 52

How does corrosion of the fixings lead to a defective roof sheet?

Answer 52

- The expansion of the fixings leads to the cracking of the sheets and then subsequent water ingress.

Question 53

How does moss growth cause defects and leaking to the sheets?

Answer 53

- Carbonation increases porosity and in damp conditions the surface is suitable for moss and algae growth. - The algae produces acidic run off which damages other components

Question 54

What remedial works can you undertake to asbestos cement roof sheets?

Answer 54

- Encapsulation - Overlaying - Full replacement

Question 55

Describe how you would replace an asbestos cement roof.

Answer 55

- Consult HSE guidance note A14 and A12 which relates to the handling of asbestos and the cleaning of it during removal. - Protect nearby surfaces with sheeting - Dampen and remove fasteners and place in a waste container - Double wrap large pieces in bags and seal - Dispose of waste at a licensed disposal centre.

Question 56

How would you identify carbonation to a concrete frame?

Answer 56

- Cracking along the line of the reinforcement bars | - Spalling and delamination of whole areas of concrete cover

Question 57

How is carbonation caused?

Answer 57

- Atmospheric carbon dioxide reacts with water in the concrete which forms a carbonic acid that neutralises concrete’s natural alkalinity - Alkalinity of concrete is reduced, passivity lost and the steel reinforcement eventually corrodes. - Corrosion makes the steel expand which eventually makes the concrete cover crack and spall off.

Question 58

How do you identify that carbonation has occurred?

Answer 58

- Visual inspection - Hammer test to discover unsound concrete - The depth of the carbonation can be ascertained by phenolpthalein, which is a pink dye that indicates where no carbonation has occurred.

Question 59

What repair options can be undertaken to address carbonated concrete?

Answer 59

- Isolated replacement - Electrochemical re-alkalisation - Cathodic protection

Question 60

Tell me how you would undertake isolated repairs to carbonated concrete?

Answer 60

- Cut out the concrete surrounding the rebar and over the fully corroded length. - Clean the steel reinforcement bar and apply corrosion inhibitor i.e. Sika/Fosroc product - If badly corroded replace the steel bar by welding new piece to existing - Replace the concrete cover with proprietary product to restore alkalinity - Apply anti-carbonation product to external surface.

Question 61

How does cathodic protection work?

Answer 61

- In corrosion cells anodes attract oxides which causes the deterioration whilst cathodes do not. - If an electrical current can be applied to metal it can be made into a cathode. - An anode system, coating or mesh is sprayed or fixed to the whole surface of the concrete and a current is applied which then passes into the reinforcement.

Question 62

What are the signs of cavity wall failure?

Answer 62

- Horizontal cracks to mortar joints at regular intervals - Expansion of the outer leaf of brickwork - Wall bulges at 900mm horizontally and 450mm vertically.

Question 63

What causes cavity wall tie failure?

Answer 63

- Corrosion of the ties due to poorly galvanised ties between 1960s and early 1980s. - Corrosion of embedded tie in black ash mortar due to chemical action (sulphates). - Wall ties may have been incorrectly placed or be insufficient in number.

Question 64

What are the ways wall tie corrosion can be remedied?

Answer 64

- Resin fixed - Mechanically fixed - Cementitious wall anchors

Question 65

How are cementitious wall anchors installed?

Answer 65

- Holes are drilled, ties installed and tightened to required torque. - Cracked brickwork and mortar can be replaced.

Question 66

What are the causes of cracking to the ground bearing floor slab?

Answer 66

- If soil contains high sulphates level and no DPM is installed - Hardcore could be contaminated with high sulphates - Sulphate may become mobile due to a broken drain or high water table.

Question 67

Can you describe the process of sulphate attack to the slab?

Answer 67

- Soluble sulphate enters the concrete - Water evaporates leaving the sulphates - Water then reacts with calcium hydroxide causing expansion - Concrete cracks due to expansion

Question 68

How would you address a concrete slab that is cracking and delaminating?

Answer 68

- Remove the source of soluble sulphates and repair the drain - Break up the concrete slab and the hardcore and replace, installed with new DPM.

Question 69

Can you name some typical defects to 1960s concrete high rise buildings?

Answer 69

- Failed asphalt roof coverings - Carbonation - High chloride content to frame - Condensation

Question 70

What defects can occur to mastic asphalt roof coverings?

Answer 70

- Crazing - Cracking - Blisters - Ponding

Question 71

How is crazing caused to asphalt roof coverings?

Answer 71

- By a lack of solar reflective treatment and ponding through the expansion of the material in hot weather and contraction in cold weather.

Question 72

How is cracking of the covering caused to asphalt roof coverings?

Answer 72

- Differential settlement and movement between asphalt and the substrate often due to the absence of an isolating membrane.

Question 73

How are blisters caused to asphalt roof coverings?

Answer 73

- By trapped moisture as some concrete roofs are asphalted before they are completely dry.

Question 74

How is ponding caused to asphalt roof coverings?

Answer 74

- Inadequate falls and poor workmanship.

Question 75

What options are available to address defects to asphalt flat roofs?

Answer 75

- Isolated repairs - Encapsulation (application of a liquid applied membranes) - Total replacement

Question 76

Can you talk me through the process of undertaking isolated repairs to mastic asphalt?

Answer 76

- Hot poultice repairs are carried out by first covering the defective area with molten asphalt so that underlying material is softened. - The existing defective, now softened, mastic is then removed to a depth of 10mm and a width of approximately 75mm. - New molten asphalt is then poured in its place and a lap joint is formed with the surrounding existing asphalt.

Question 77

How would you identify carbonation to a concrete frame?

Answer 77

- Cracking along the line of the reinforcement bars. | - Spalling and delamination of whole areas of concrete cover.

Question 78

How is carbonation caused?

Answer 78

- Atmospheric carbon dioxide reacts with the water in concrete which forms a carbonic acid which neutralises concrete’s natural alkalinity. - Alkalinity of concrete is reduced, passivity is lost and the steel reinforcement eventually corrodes. - Corrosion makes the steel expand, which eventually makes the concrete cover crack and spall off.

Question 79

How do you identify that carbonation has occurred?

Answer 79

- Visual inspection - Hammer test to discover unsound concrete - The depth of carbonation is ascertained by phenolthalein which is pink dye which indicates where no carbonation has occurred.

Question 80

What repair options can be undertaken to address carbonated concrete?

Answer 80

- Isolated replacement - Electrochemical re-alkalisation - Cathodic protection

Question 81

Tell me how you would undertake isolated repairs to carbonated concrete?

Answer 81

- Cut out the concrete surrounding the rebar and over the full corroded length - Clean the steel reinforcement bar and apply corrosion inhibitor i.e. Sika/Fosroc product. - If badly corroded, replace the steel bar by welding new piece to existing. - Replace the concrete cover with proprietary product to restore alkalinity. - Apply anti-carbonation product to external surface.

Question 82

How does cathodic protection work?

Answer 82

- In corrosion cells anodes attracts oxides which causes the deterioration whilst cathodes do not. - If an electric current can be applied to metal it can be made into a cathode. - An anode system, coating or mesh is sprayed or fixed to the whole surface of the concrete. - A current is applied which then passes to the reinforcement.

Question 83

How can you identify that chloride is present in the concrete?

Answer 83

- Localised cracking due to how the steel corrodes. - Rust staining - Localised delamination of cover due to the expansion of the rebar.

Question 84

What are the causes of chloride introduction to concrete in a high rise building?

Answer 84

- Introduced as an accelerator during the mixing process - Naturally occurring through unwashed marine aggregates - External contamination through de-icing salts - Chloride ions can break down the passive layer of alkalinity around the rebar.

Question 85

How can you tell the difference between concrete that is affected by carbonation and concrete that has been affected by calcium chloride?

Answer 85

- Calcium chloride causes the rebar to corrode at a darker colour than carbonation - The effects of calcium chloride to steel reinforcement are localised and as such is termed ‘pitting corrosion’.

Question 86

How would you advise your client to remedy concrete affected by high chloride content?

Answer 86

- Undertake patch repairs similar to carbonation i.e. clean/replace corroded sections of rebar - Adopt a cathodic protection system to prevent further effects by the chloride ions.

Question 87

What is condensation?

Answer 87

- Condensation is when warm moisture vapour comes into contact with a cold surface and cools to the dew point. - At the dew point, the water vapour turns into a liquid on the cold surface

Question 88

What is the dew point in relation to condensation?

Answer 88

- The atmospheric temperature which varies according to pressure and humidity, below which water droplets begin to condensate and dew forms.

Question 89

What are the symptoms of condensation?

Answer 89

- Surfaces become misty with stains running down the walls | - Damp patches with no definitive edges occur along with mould growth.

Question 90

What are the typical causes of condensation?

Answer 90

- Human activity such as washing, cooking etc. - Cold bridges in well insulated buildings. - Poor ventilation.

Question 91

How do you repair condensation?

Answer 91

- Reduce dampness in the building surfaces by: o Improving ventilation o Improving insulation o Increasing heating levels o Alter the living habits of the occupants.

Question 92

What is cold bridging?

Answer 92

- Localised areas in buildings with a higher thermal conductivity than in adjacent areas, resulting in an overall reduction in the thermal insulation of the building.

Question 93

What causes cold bridging?

Answer 93

- Differences in construction such as a break in the continuity or a penetration of the insulation. - Lintels over doors and windows in the 1960s and 70s were plagued by this problem.

Question 94

What remedies are available to a property suffering from areas of cold bridging?

Answer 94

- Ensuring that there is adequate ventilation - During construction, ensuring that cavities are closed and that vertical/horizontal dpcs are incorporated into construction.

Question 95

Can you name some typical defects to 1980s steel framed buildings?

Answer 95

- Cut edge corrosion to profiled metal roof sheets - UV deterioratin of roof lights - Failed metal cladding coatings - Composite cladding panels

Question 96

What are the symptoms of cut edge corrosion?

Answer 96

- The protective coating starts to peel back at the lap joints – approximately 10mm is considered defective.

Question 97

What are the causes of cut edge corrosion?

Answer 97

- When the roof sheets are cut in the factory the coating is damaged and micro-cracking occurs which allows the admission of moisture and leads to corrosion. - Water also get trapped at the lap joints and the coating lifting exacerbates.

Question 98

How do you remedy cut edge corrosion?

Answer 98

- Clean the affected area and remove the defective coatings. - Gun apply a sealant to bridge the gap (25mm either side of joint) - Brush apply one coat of seamsil (37mm) either side of the joint.

Question 99

How do you identify that UV deterioration has taken place to GRP rooflights?

Answer 99

- The exterior gel coat to the rooflights deteriorated and the glass fibres are exposed due to UV exposure. - The sheets become brittle and hard and are easily damaged. - Leaks become more likely as does moss growth. - Light transmission is reduced.

Question 100

How would you remedy a UV deteriorated rooflight?

Answer 100

- Replace the rooflight. - Or apply a translucent resin coating such as HD Sharmans’ Delglaze once the surface has been suitably cleaned and dried.

Question 101

What are the signs of failed metal cladding coating?

Answer 101

- Plastisol, PVF2 etc. coating starts to peel back and flake away in places. - Corrosion could be evident to exposed cladding below.

Question 102

What are the causes of failed metal cladding coating?

Answer 102

- Coating may have lost adhesion due to poorly prepared substrate - The coating may have broken down due to UV and temperature change - The recommended repaint guidelines are often ignored (every ten years)

Question 103

What would you advise to do to address failed cladding coatings?

Answer 103

- Thoroughly prepare the substrates and spray apply a new coating such as Girocoat or steel seal.

Question 104

Why are composite cladding panels classed as a defect?

Answer 104

- The combustability and fire spread is the main concern as there is a risk of collapse due to instability. - Expanded polystyrene is the worst infill material as it promotes rapid fire spread.

Question 105

What are the other types of infill material and when did the LPCB become aware of the dangers?

Answer 105

- EPS – Expanded polystyrene - PUR – polyurethane foam - PIR – polyisocyanurate foam - PF – phenolic foam - Pre-2000 are likely to have a PUR foam

Question 106

What remedy would you suggest to your client in the event of discovering non-LPCB compliant composite cladding?

Answer 106

- Send a sample to the lab for testing to ascertain the material being dealt with. - PIR can be engineered to comply.

Question 107

What are the typical life spans for flat roof coverings asphalt/built up felts?

Answer 107

- Asphalt – 25 years - Built up felt – 10-20 years - GRP (Fibreglass) – 20-30 years - Green roof – 40-50 years - EPDM – 50 years

Question 108

Explain the difference between warm and cold deck roof construction

Answer 108

- Cold roof – the thermal insulation layer is located immediately above or between the ceiling joists with the vapour control layer below the insulation, so everything above the insulation including rafters, roof space etc. will be colder than the living space beneath it. When warm/damp air permeates up through the ceiling and reaches the cold roof space, the change in temperature can result in condensation forming so adequate roof space ventilation must be provided to remove this air - Warm roof – the insulation layer is laid on top of the roof structure with the structural deck and its supports being at a temperature closer to that of the building’s interior. The vapour control layer is placed below the insulation and the plywood/osb board sits on top.

Question 109

What are the common defects associated with sheet lead coverings?

Answer 109

- Lead is extremely sensitive to changes in temperature – in temperature fluctuations the lead will expand/contract in cycles. Where bay sizes exceed maximum recommended sizes there will be rippling and cracking. - The junction along the length of each bay is normally formed with a roll or welted upstand. Inappropriate fixing will result in buckling and cracking of the sheet, often along the roll. - Foot damage causing sharp debris to pierce the lead - Corrosion pinholes caused by acid run off from algae, moss and types of wood - Condensation dampness due to poor ventilation under the lead - Inadequate overlaps at lead joints or joints are poorly made - Puddles caused by inadequate falls/slopes on roofs and large gutters.

Question 110

What do the lead codes refer to?

Answer 110

- The thickness of the lead that should be used to best suit a project - Ranging from Code 3 to Code 8 separating lead into different thickness and weight, equating to a specific weight measured in kilograms per square meter. - Each code has been specifically classified for different purposes to ensure lead functions to a high quality standard and is installed correctly.

Question 111

What is a tingle?

Answer 111

- Slate straps that are commonly used for repairing broken or slipped slate roof tiles by fixing it to the batten and turning the end up to hold the repaired slate in place. - More temporary measure to keep the slates in place until repairs can be carried out. - Usually formed from lead and nailed to the roofing battens, taken underneath the loose tiles and then neatly folded around the tail of the slate.

Question 112

Name the common defects associated with slate roof coverings?

Answer 112

- Nail sickness (original fixings made of iron/poor quality galvanised steel and will corrode over time, which can cause nails to snap allowing the slate to slip). - Broken slates – absorb water over time and eventually start to fracture/break. - Slipped slates – nail breakage or enlargement of the nail hole as a result of natural decay. - Delamination – texture is layered and when it starts to reach the end of its life, the layers might begin to split apart, which can lead to breakages and leaks. - Flashing damage.

Question 113

What problems can arise from using two different metals next to each other?

Answer 113

- When a dissimilar metals contact each other in the presence of moisture, galvanic corrosion may result. The wet metals behave like a battery and produce an electrical current and the surface of one or both metals becomes pitted and corrode as the exchange of electrons takes place. Galvanic corrosion can seriously weaken metal parts, which eventually will fail. Structures could collapse and piping could break/develop leaks if materials are incompatible. - The most common dissimilar metal combinations are carbon steel/aluminium and carbon steel/copper. When in contact they should be coated with nonconductive material, such as epoxy or phenolic paint. Gaskets can also be used to separate metals.

Question 114

How are rainwater goods sized and what section of the building regulations relates to this?

Answer 114

- Part H (Drainage and Water Disposal) - The size of guttering should be determined by the area of the roof and the anticipated rainfall intensity ( amount of water anticipated in a 2 minute rainstorm). There are a number of calculators that can be used to size gutters and downpipes based on this information.

Question 115

What problems are likely to be associated with a leaking flat roof with woodwool slab decking and what remedial works should be considered?

Answer 115

- During the 1950s-70s woodwool was used as a permanent formwork as a convenient means of providing thermal insulation properties to exposed floor slabs. - Because of the permanent shuttering conceals the steel reinforcement it is difficult to know whether full compaction and coverage of the steel reinforcement has been achieved and whether it was placed properly and was properly embedded in concrete. The spacers may have been displaced and the steel could rest directly on the top of the surface of the slab and as a result strength and fireproofing would be compromised. - This could lead to a poor or failed bond between the woodwool and the hardened concrete, excessive penetration of the grout/mortar into the woodwool leading to the impairment of the concrete and honeycombing/voiding of the concrete beneath the reinforcement. - This would leave the steel reinforcement exposed to any roof leaks and could lead to corrosion and the weakening of the reinforcement. - Non-destructive testing can be undertaken to identify whether any issues exist, although physical sampling is likely to be more reliable. Removal of the shuttering and repairs using hand placed mortars/sprayed concrete may be necessary if defects are found.

Question 116

What problems are associated with replacing slated roof coverings with new concrete tiles?

Answer 116

- Sagging, as concrete tiles are heavier than slates, and this can occur if the roof timbers have not been strengthened. - Roof spread where rafters have pushed the walls outwards and sunk in the middle. In severe cases, structural work may be needed and a structural engineer should be consulted.

Question 117

What are the main defects caused to flat roofs?

Answer 117

- Excessive movement - Entrapped moisture - Solar degradation - User negligence

Question 118

What causes excessive movement to flat roofs?

Answer 118

- Drying shrinkage (moisture movement of timber and concrete) - Deflection of the decking under the load of the covering etc. - Structural failure of the decking - Thermal changes in the deck and coverings

Question 119

What are some of the results of excessive movement in flat roofs?

Answer 119

- Roof sagging - Localised ponding - Splitting/tearing of the roof coverings - Water ingress at pipe and vent junctions

Question 120

What causes moisture to become entrapped in a flat roof?

Answer 120

- Lack of effective ventilation to remove vapour - Inadequate or missing moisture barrier - Laying covering directly on to wet decking or snow or not allowing free water to evaporate from concrete.

Question 121

From an inspection of a flat roof how could you tell moisture was entrapped?

Answer 121

- Blistering/bubbling of the surface as a result of hot weather.

Question 122

How would you identify if solar degradation had occurred to a flat roof?

Answer 122

- Blistering and cracking would appear on the surface. - Crazing through the surface. - Asphalt in particular becomes brittle.

Question 123

What are the causes of solar degradation in flat roofs?

Answer 123

- Inadequate solar protection using chippings/paint/tiles. | - Wind scouring of the chippings.

Question 124

What are the causes of user negligence to flat roofs?

Answer 124

- Impact damage to surface - Specifying an inadequate number of movement joints - Designing ineffective ventilation - Short life of materials and incorrect falls - Overheating of asphalt during laying - Poorly laid reflective chippings

Question 125

What are common defects to felt flat roofs?

Answer 125

- Differential movement - Condensation - Insufficient falls - Loss of protective chippings - Skirtings and parapets - Sealing of lap joints

Question 126

Why is differential movement a problem with felt flat roofs?

Answer 126

- Felt is liable to crack through differential movement between felt and the substrate and the shrinkage of the base due to thermal changes.

Question 127

What problems will condensation cause to a felt flat roof?

Answer 127

- Condensation can become entrapped moisture and can create fungal growth and cause the felt to lift and cause blisters.

Question 128

What measures can you take to prevent condensation occurring in a felt flat roof?

Answer 128

- Ensure a vaper barrier is installed and that the roof is sufficiently ventilated.

Question 129

How do loose protective chippings create problems with flat roofs?

Answer 129

- Loose protective chippings can cause choking of gutters and penetrate felt providing a source of moisture ingress. - Reflective paints are also prone to crazing.

Question 130

How can problems occur at the skirting and wall parapets with felt flat roofs?

Answer 130

- Differential movement between skirting and parapets can cause failure of the coatings - Skirtings are formed at parapets by turning up two layers of felt against abutments to a height of 150mm.

Question 131

How can lap joints cause defects to felt flat roofs?

Answer 131

- Welding joints give a higher strength than adhesives, so poorly applied adhesives instead of welding could create problems. - Stones and grit become trapped beneath the membrane at the time of laying which can cause holes to form

Question 132

Why would you specify mastic asphalt as a roof covering?

Answer 132

Why would you specify mastic asphalt as a roof covering? - It provides a jointless covering with no need for welds, rolls, drips and seams. - It is an unobstructed smooth finish which is ideal for roofs with traffic.

Question 133

What are the common defects you’d expect to encounter on mastic asphalt roofs?

Answer 133

- Ponding - Blistering - Cracking - Differential movement at joints - Changes in temperature

Question 134

Why is ponding water a defect to a mastic asphalt flat roof?

Answer 134

- Stresses imposed in weather will tend to cause the material to expand in the summer and consequently contract in winter. - They will cause map pattern cracking across the roof - The ponding will then be a prolonged source of water ingress rather than falling away.

Question 135

When would blisters appear in a mastic asphalt roof?

Answer 135

- Blisters are prone to appear in a concrete deck or deck with a lightweight concrete screed due to the concrete not fully drying out before being asphalted. - Heat from the sun creates expansion of any moisture vapour which can lift the asphalt from the concrete locally. - Rainwater trapped under asphalt can also lead to blisters in the same way.

Question 136

How does cracking occur to asphalted flat roofs?

Answer 136

- Cracking is fairly common to old asphalted roofs and is caused by the movement of the substructure and the asphalt due to the absence of an isolating membrane. - Old asphalt roofs can also crack by becoming brittle or through excessive wear.

Question 137

Can you name where differential settlement can occur in an asphalted flat roof?

Answer 137

- Joints between the horizontal surfaces and vertical abutments of parapet walls.

Question 138

Tell me how differential settlement can occur to an asphalt flat roof.

Answer 138

- Rainwater penetration has occurred behind asphalted skirting either because the skirting was not properly turned back at the brick joint or the cover flashing has been omitted.

Question 139

Can you name some common defects to flat lead roofs?

Answer 139

- Lead being of insufficient code - Incorrect specification of underlay - Incorrect spacing of joints or incorrect fixing - Excessive number of soldered joints - Punctures in the surface - Pitting and corrosion of lead sheets (internally and externally) - Wind uplift.

Question 140

What remedial measures would you undertake to a lead roof with an insufficient existing lead covering?

Answer 140

- Check the original specification if possible and replace the lead with a thicker code.

Question 141

How would you address a puncture in a lead flat roof?

Answer 141

- Remove the risk of the damage and patch repair with a sheet weld.

Question 142

How would you address a lead flat roof which has suffered from wind uplift?

Answer 142

- Increase the number of fixings | - If in an exposed area, consider replacement of the existing lead with a higher code.

Question 143

What causes pitting corrosion of the surface internally and externally and how would you remedy the issue?

Answer 143

- Externally, corrosion can be caused by attacks by aggressive chemicals off adjacent roofs. - The remedy would be to remove the offending materials on the adjacent roof if possible and replace the lead with a thicker code or a different material unaffected by the run off. - Alternatively a sacrificial flashing can be installed. - Corrosion is caused to the underside by condensation, perhaps from entrapped moisture from the deck or insufficient ventilation. - Relay the affected lead sheet incorporating insulation, ventilation and vapour barriers.

Question 144

If you are dealing with a flat roof which is centuries old, what defects might you expect to encounter?

Answer 144

- Lead roods constructed centuries ago were often laid in sheets too long and wide - Over time the sheets will have suffered thermal movements by climatic conditions - The fixings are often poor and the drips too shallow - Therefor wind uplift could take place as well as moisture ingress.

Question 145

What defects would you expect to find with a liquid applied coating to a flat roof covering?

Answer 145

- Splits in the roof covering - Fractures in verges, flashings and abutments - Failure of the material where dressed around pipes, ducts and roof lights - Loss of bind between coating material and substrate

Question 146

Why do buildings crack?

Answer 146

- Temperature changes - Initial drying (shrinkage over weeks or years) - Wetting and drying (expansion and contraction) - Loss of volatiles (irreversible shrinkage over hours or years) - Freezing and thawing of absorbed water - Sub-surface crystallisation or soluble salts (crypto-efflorescence) - Sulphate attack (permanent expansion over months to years) - Corrosion/oxidation (permanent expansion over months to years) - Moisture expansion of ceramics (permanent expansion over decades) - Carbonation (permanent shrinkage over 1-50 years depending on porosity) - Alkali silica reaction (ASR) (irreversible expansion over many years) - Hydration of oxides and unstable slag aggregates (permanent expansion over months to a few years) - Dead and imposed loading on structure within design limits (elastic and creep deflection over years) - Structural loading (elastic and creep deflection over years) - Loading of ground/foundations (consolidation – settlement over months to years) - Settlement, mining, subsidence, swallow holes, land slips, soil creeps, earthquakes - Traffic, machinery, sonic booms, mining, explosions

Question 147

Name some of the causes of stepped cracking in brickwork.

Answer 147

- Subsidence - Heave - Settlement - Point loading - Thermal and differential movement - Lintel failure

Question 148

How can cracked, worn or spalling bricks be repaired?

Answer 148

- Remove all damaged parts of the brickwork and patch up what is left using fillers made of lime mortar mixed with brick dust to allow for a colour match. - Replace all damaged bricks that are beyond repair. - It may be possible to flip a brick around to use the undamaged inner face outwards and filling in behind it to ensure the bricks match.

Question 149

Cracking has been identified to the sides of a bay window to a traditionally constructed property circa 1900s. What are the potential causes?

Answer 149

- Bay windows in older houses commonly have foundations which are not as deep as the main part of the house. This will lead to differential movement. Cracking is likely to be minor caused by seasonal movement - Subsidence.

Question 150

What remedial works should be undertaken to rectify the problems of the previous question?

Answer 150

- Insert an expansion joint to accommodate future differential movement with a flexible mastic sealant to keep the structure weathertight. - The cracks are likely cosmetic and non-progressive, but if re-pointed will recur seasonally. - Where there is extreme cracking due to subsidence, the standard approach is to identify and remedy the underlying cause (drains, trees, foliage), but where damage is severe it may be necessary to excavate beneath the foundation levels to a stable ground and underpin with concrete.

Question 151

Can you name some typical wall movement defects?

Answer 151

- Ballooning in walls - Bulging due to inadequate restraints - Tensile cracking in brick walls - Oversailing - Movement in parapet walls - Ratcheting

Question 152

What is ballooning in walls and how might it be caused?

Answer 152

- A response to unrestrained expansive or outwards forces. | - May be due to overloaded floors or sagging roofs

Question 153

What might cause a wall to bulge outwards?

Answer 153

- Potentially caused by overloading of the floors which transmit the loads to the walls. - This can be made worse by a lack of restraint from the floor structure.

Question 154

Why might a crack run straight down brickwork in a wall and not the surrounding mortar?

Answer 154

- The tensile capacity of brickwork and mortar is relatively low. - Normally the tensile strength of mortar is lower than brickwork causing the crack to follow the path of least resistance. - Sometimes, if the mix is wrong, the mortar is stronger and this will cause the crack to go straight through the brickwork instead.

Question 155

What is oversailing in a wall?

Answer 155

- Oversailing occurs at the corner of buildings and is a dislocation of the brickwork around DPC level.

Question 156

What causes oversailing in a brick wall?

Answer 156

- Expansion of walls meeting at a corner result in the wall slipping across the DPC during expansion, but not withdrawing on contraction. - The forces on contraction are not great enough to pull back the wall.

Question 157

Why do parapet walls move?

Answer 157

- Movement is often due to a lack of self-weight or restraint. - The walls are often subject to thermal and moisture related movements. - Oversailing can occur in corners.

Question 158

What is ratcheting in a wall?

Answer 158

- When tension cracks appear in a long wall.

Question 159

Where would you expect to find rising damp?

Answer 159

- Along the base of traditional masonry wall that is built off the ground - Tide marks rise up as much as 1m up the wall on average

Question 160

How can you identify rising damp?

Answer 160

- There is a continuous horizontal tidemark of ground salt contamination at around a metre in height. - Sporadic staining/discolouration (brown staining) up to around 300-900mm in height - Blistering, flaking of paintwork and plasters, visible salt accumulation. - Damage, rotting and deterioration to joinery and structural timbers - Sulphate action - Corrosion of metals, e.g. edge beads - Musty smells - Condensation

Question 161

How does rising damp occur?

Answer 161

- It is caused by capillary action drawing moisture up through porous elements of a building’s fabric. It rises vertically up a wall.

Question 162

When did damp proof courses become compulsory in buildings?

Answer 162

1875

Question 163

When did damp proof membranes become compulsory in buildings?

Answer 163

1965

Question 164

Explain cold bridging

Answer 164

- An area of a building’s fabric which has a higher thermal transmission (i.e. the area is a poorer thermal insulator) than the surrounding parts of the fabric. - It occurs where materials have a much higher thermal conductivity than the surrounding material penetrate the thermal envelope, or where there are discontinuaties of the thermal envelope. - As heat flows through the fabric (to the cold air outside) the surfaces of the interior side of the bridge become colder resulting in a reduction in the overall thermal insulation and performance of the structure. - It can result in an increase in fabric conduction heat loss - An increase in solar gains during the summer - Reduction in internal surface temperatures - Cold spots and stratification cold occurring within the building - Increased risk of interstitial condensation, which may lead to staining and mould growth - Reduction in internal air quality due to mould/condensation - Damage to building components - Found around window and door openings and balconies.

Question 165

Explain how you would deal with a case of rising damp in a building.

Answer 165

- Replace the affected plaster as hydroscopic nitrates and chlorides need to be dealt with. - If necessary insert a new DPC, either by physical insertion or chemical injection o Physical insertion – reliable barrier and appropriate where total certainty required. Necessary to join new DPC to DPM, but they are expensive and can only be laid in horizontal courses – difficult with stonework. o Chemical insertion – cheapest and most common method – by pressure or gravity. - May be possible to reduce the ground levels and controlling external water systems may help. - In a listed property it may be necessary to install a perimeter drain.

Question 166

What signs indicate condensation within a property and what steps would you take to eliminate this?

Answer 166

- Can be confused with rising and penetrating damp - The wall has a misty surface. - Stains/streaks of water running down the wall. - Damp patches with no definitive edges. - Dampness behind cupboards against external walls. - Patches of mould growth, particularly in cold corners in the classic crescent or hourglass shape. Also shows up at a cold bridge, e.g. poorly fitted windows and doors. - Pinpoint damp contours with a moisture meter – use deep wall probes – if readings are low at centre height, unlikely to be rising or penetrating damp. Also salt analysis is negative for chlorides or nitrates. Establish dew point by measuring surface temperature and relative humidity. If surface temperature below dew point = condensation. Use a protimeter damp check which records condensation over 24 hours. - Best way to reduce moulds is to reduce dampness – improve quality of insulation on affected surfaces (double glazing), levels of heating (central heating), improving ventilation (window vents, extracts, heat recovery), altering the living habits of the residents (dry clothes outdoors, etc.)

Question 167

Explain how you would deal with interstitial condensation.

Answer 167

- Most walls are porous and allow water vapour to slowly pass through if the internal wall surface temperature is above dew point, but the centre of the wall is below, there is a risk of interstitial condensation. It occurs inside of the wall, instead of on the surface, which is common with solid brick walls, but is not commonly an issue with cavity walls. - May cause dampness, but it should not affect the durability of the bricks/blocks. - If it occurs in timber/metal, action is required to prevent rot and corrosion. It can be reduced by incorporating vapour control layer on the warm side of the insulation.

Question 168

What problems are likely to be associated with rendering over external brickwork?

Answer 168

- Cementitious renders are applied with the intention of sealing surfaces to prevent moisture from entering, in effect making older properties function like modern buildings, but cement mortar pointing or renders have the effect of inhibiting evaporation, potentially putting the ends of floor joists at risk of rotting. - Repointing mortar joints in this way prevents them from breathing, forcing the moisture to evaporate via the surrounding brick or stonework, where the effects of frost action/crystallisation can cause severe spalling/erosion of the wall surface. - The inflexible, brittle nature of hard modern cement based mortars and renders means they are ill equipped t accommodate movement without cracking. Moisture will then penetrate through small cracks and become trapped. - Sealing up internal walls with modern gypsum compounds the problem by blocking any escape route for moisture internally. - Cement renders tend to be very dense and highly resistant to vapour transfer. Permeability of the finish decreases as more masonry paint is applied and the risk of water entrapment and interstitial condensation rises. - Such water retention can be harmful to a building, especially if the masonry is constructed from lime mortar, which will deteriorate and lead to delamination and cracking via the effects of freezing and thawing.

Question 169

What works might be specified to rectify damp ingress to a basement of a building constructed circa 1900?

Answer 169

- A simple land drain problem/broken surface or foul water drain can be repaired/replaced, but care must be exercised in laying new land drains as a radical drying of the subsoil leads to shrinkage, especially in clay areas and often causes movement in buildings. - If the cellar suffers minor flooding, then the creation of a sump drained by a pump with a water sensor/float switch will often work reasonably well if the space is only used for storage. - In order to avoid preventing trapping moisture in the walls, tanking should be avoided and mechanical ventilation should be introduced to the space. Remove all impermeable materials and replace with breathable materials.

Question 170

What works might be specified to rectify damp ingress to a basement of a modern building formed of reinforced concrete?

Answer 170

- Where it is possible to dig down externally, water ingress can be reduced by introducing a water proof membrane (polypropylene) against the external face of the retaining wall with a land drain at the bottom – not perfect if this cannot be connected to a horizontal dpm across the floor, but good results can be achieved. - Internal tanking can be used if the original internal surface of floors/walls can be lost from view. - The laying of drains internally to take excess water out of the building and tanking of the internal space with polypropylene or geotextile lining to the floors and walls can be very effective. Walls can then be lined with plaster/blockwork and plaster, and floors re-laid with new concrete and a screeded finish to create a solid and level working surface. The damp is not removed but its presence no longer affects the use of the space. The main issue is damp remains in situ unless carried out to the exterior of the fabric. A membrane applied to the inner face relies on adhesion alone to resist water pressure. Expensive. - Approved Doc C requires that basements have either barrier protection, protection by the structure itself, or protection by an internal water management system, such as a cavity drain leading to a sump with pumps.

Question 171

Explain some of the dangers of using a damp meter?

Answer 171

- They measure the resistance of electricity between two electrodes and relate this to the amount of moisture they are scaled to, usually timber. When used on other materials they can therefore be misleading. It does, however, give a preliminary sense of moisture content, with measurements below 17% being dry (green), 17-20% at risk (yellow) and 20%+ wet (red). - Also salt analysis is negative for chlorides or nitrates. Establish dew point by measuring surface temperature and relative humidity. - Foil backed plaster can give 100% relative reading. - Best used for comparison measures over time

Question 172

What are the two most common types of wood boring insects?

Answer 172

- Common furniture beetle - Deathwatch beetle - House longhorn beetle - Wood Boring weevil

Question 173

What are the key indicators to identification of the different wood boring insects?

Answer 173

- Size and shape of the flight holes - Evidence of any dead beetles - Whether hardwood or softwood is affected - Moisture content of the timber - Time of year the beetles emerge

Question 174

How would you identify whether rot was wet or dry?

Answer 174

- Main difference relates to the dry rot fungus tending to decay at lower moisture contents (20-30% rather than 30-50%) and the wood tends to be left in a dry state after dry rot attack. - Wet rot – most common coniophora puteana (cellar fungus)  More common than dry rot  Need a higher moisture content (45-60%, temps -30-+40 degrees)  Localised and not as destructive as dry rot – it does not spread beyond the immediate area and growns on wetter timbers.  Cracked appearance that my crumble to the touch when dry  Shrinkage  Damp, musty smell  Can be either white or brown o White rot  Decay appears white as the fungus digests the lignin and cellulose  Gives the timber a soft, spongy feel when touched o Brown rot  Darker appearance as it feeds on sugars and cellulose giving a brown appearance.  Smaller cuboidal cracking, may leave a thin veneer of sound timber  Cellar fungus – mycelium – brown, fruiting body – flat, plate like, greenish brown centre, yellow margins and knobbly surface. - Dry rot (serpula lacrymans) o Thrives in damp wood, but not wet wood (20-40% MC, 0-26 degrees) o Indicative odour – fusty mushroomy smell o Spreads beyond the immediate area, searching for its own moisture and feeding on available timbers o Rarely found externally o Spores (rust red), hyphae (fine white tendrils), mycelium (cotton wool like substance – grey with lilac yellow patches if dry), fruiting body (reddish brown with white margins – flat plate/bracket shape) o Large cuboidal cracking (brown rot) o Shrinking and dry, darker, brittle, crumbly timber. o Signs of dry rot in flooring can be hard to see as it occurs under the floorboards – you may feel that the floor feels bouncy, drops away from the skirting boards or floorboards and may start to creak more.

Question 175

What is brown rot?

Answer 175

- Caused by fungi that do not degrade the lignin. - Residue left after the action of the brown rot fungus is a brown amorphous substance, rich in lignin. - The lignin is modified to allow access to the cellulose, the main nutrient of the brown rot fungus. - Main fungal decay in buildings caused by brown rot fungi - Cause the wood to become darker in colour and crack across the grain - When dry, very decayed wood will crumble to dust. - Common brown rots – coniophora puteana (cellar fungus). Also mine or pore fungus.

Question 176

What are the problems associated with dry rot?

Answer 176

- It brings about the dramatic decay of timber and is able to spread through a building from one timber location to another across non-nutritional surfaces. - Serious impact on UK housing stock and causes concern when dealing with the conservation of buildings of architectural or historic value. - It is the most virulent form of fungal attack in building timbers and buildings with traditional construction are particularly vulnerable to this form of decay. - Vast majority of UK properties contain a significant amount of wood and to detect the type and extent of fungal decay, remedial measures may entail the loss of decorative finishes and extensive exposure and damage to the fabric of the building – expensive.

Question 177

Timber decay is often found to suspended timber floors in traditionally constructed buildings. What does the occupier commonly do to the property to lead to this problem?

Answer 177

- Obstructing air vents by installing insulation, raised external ground levels or a house extension blocks ventilation paths. - Concrete ground bearing slabs and foundations are at risk when in soils that contain high sulphate levels or contaminated hardcore and where they are not separated from the ground by suitable polythene sheeting/membranes. - Sets up stresses in the mortar/concrete and results in significant deterioration and damage. - More common in 1950s-60s due to hardcore used, particularly in mining areas. - Signs include heaving and cracking of the floor, lumpiness and doming, traces of salts on the floor surface.

Question 178

Explain how you have (would) deal with a wood boring beetle infestation in a building.

Answer 178

- Identify the type of insect by reviewing the flight hole size and shape, the size and appearance of emerging beetles, the time of year adults are emerging, the size and shape of any frass, along with the location, type and moisture content of the timber. - Furniture beetle/woodworm – brush treatment with organic solvent or micro-emulsion paste, fumigation with hazardous gasses, freezing and heating (smaller items), spray treatment (preservative), injection treatments. Infestation mostly restricted to residual sapwood and infestations will die if timber remains dry. - Deathwatch beetle – determine if activity is current (paper over flight holes and monitor emergence annually). Rectify sources of water penetration, increase ventilation. Spray or brush treat infested surfaces with a spirit based insecticide. Coat accessible surfaces with preservative paste, drilling holes at 100mm intervals if appropriate to ¾ depth. Heat treatment the most effective and minimises damage to timber, by maintaining relative humidity at 50%, but expensive. Fumigation, reduce moisture and replace is necessary and pressure injection/gravity feed application. - Weevil – no insecticide treatment – remove source of dampness, dry out and replace decayed timber. - Longhorn beetle – organic solvent, micro-emulsion paste. Inspect and remove powdered material to determine extent, remove and burn affected timber and report to BRE.

Question 179

Explain how you would deal with a case of wet rot in a building.

Answer 179

- Undertake a detailed survey to identify the timber affected - Isolate the affected timber from the source of moisture and dry out the area - If advanced, the affected areas will need to be cut out and new sections spliced in. - A moisture meter should be used to ensure that the full extent of the potential area of rot has been detected.

Question 180

Explain how you would deal with a case of dry rot in a building.

Answer 180

- Undertake a detailed survey to identify the areas of timber and masonry affected, which may need to include intrusive techniques. - If the timber has been structurally weakened, replacement of the weakened timbers with preservative pre-treated timber, concrete or steel units is needed. - As much decayed timber should be removed as possible – standard to cut out infected areas and 300mm of adjacent sound timber to ensure that the all of the affected timbers have been removed. - Spores can remain dormant for up to 10 years and the source of dampness should be eliminated and the timber should be dried out to prevent further infection. - Timbers at risk can be treated with preservative to prevent decay, but has to penetrate deep into the timber to be effective. - Dry rot masonry fluid can be applied to the surface of damp and infected walls. - 21st century approach to remove moisture, as dry rot cannot be sustained in dry timber. Recommended in historic buildings – dry rot can remain dormant even if it does not die.

Question 181

Your client owns a Grade I listed building and has found evidence of extensive dry rot. How might this be dealt with to cause minimum disturbance to the building?

Answer 181

- Provided the client is happy to take a small risk of reinfection while the property dries out, remove all sources of water penetration and dry out the area. - Expose cavities as far as practical by lifting floorboards and leave exposed for as long as possible. - Thoroughly clean out all debris and loose/unimportant decayed material from the zone of decay. - Consider the installation of a remote moisture sensing system to detect any further wetting of the structure. - Replace all decayed materials and paste treat all accessible softwood timber to within 100mm of decorated surfaces. - Treat all embedded softwood timbers by partial exposure and paste application. - Ensure insurance backed guarantees are sought rather than reliance on the installer’s own certificate.

Question 182

What are the symptoms and causes of wet rot?

Answer 182

- Dark brown colour to the timber - Very damp conditions - Cracks run longitudinally across the grain - Fruiting body rarely found inside of buildings - Causes are very damp conditions over 25% moisture content in timber and continually moist conditions e.g. faulty plumbing.

Question 183

How would you remedy timber suffering from wet rot?

Answer 183

- Isolate the affected timber from the source of moisture - Cut out the old, rot affected sections of timber and splice in new timber - Use a moisture meter to ensure that the full extent of the rot has been removed

Question 184

Can you describe the typical rot lifecycles?

Answer 184

- Spores are released from a fruiting body - The spores develop into hyphae which penetrate the wood - A mass of hyphae gathers to form a mycelium - The mycelium form together to create a fruiting body

Question 185

What are the common defects you might encounter in a suspended timber floor?

Answer 185

- Defective sleeper walls - Inadequate ventilation - Timber decay to joist ends - Excessive notching

Question 186

What defects might you encounter with sleeper walls?

Answer 186

- Rotting of timber wall plate - Frost action caused by wetting of the masonry - Lack of insulation - Inadequate DPC - Drying of mortar joints will lead to shrinkage cracking

Question 187

What is a hollow clay pot floor?

Answer 187

- A floor system constructed of hollow clay pots and concrete as a means of constructing fire proof floors and reducing some of the dead loads of solid construction.

Question 188

How would you identify that a hollow clay pot floor was used?

Answer 188

- Common in post war years, so could feature in a building within that era - They were used to form the voids between ribs in trough slabs.

Question 189

What are the issues with hollow clay pot floors?

Answer 189

- Voiding may occur to the concrete ribs while casting and due to the presence of the spacer bars you cannot see this take place - The posts will spall and shatter due to uneven thermal expansion. - This can lead to loss of strength and reduction in fire resistance.

Question 190

What is high alumina cement and why is it a problem?

Answer 190

- It is cement developed for its high early strength and its ability to resist chemical attack, particularly for marine applications. During the 1950s and 60s it was mainly used for the manufacture of precast prestressed components which could be manufactured quickly, offsetting the high cost. It was banned from structural use in the UK in 1976. - HAC concrete undergoes a mineralogical change known as conversion. During this phase the concrete increases in porosity, which leads to a loss of strength and a reduction in resistance to chemical attack. The higher the temperature during the casting of the concrete, the more quickly conversion occurs. - The strength of a highly converted concrete is extremely variable and substantially less than its initial strength (50%+). - Vulnerable to acid, alkaline and sulphate attack where water and chemicals are present over a long period of time at normal temperatures. - Chemical attack normally very localised and concrete typically degenerates to a chocolate brown colour and becomes very friable. - Alkaline hydrolysis in a warm moist environment characterised by white powdery deposits and severe loss of strength and integrity. - Due to sensitivity to moisture, the greatest risk lies in use of HAC in roof members.

Question 191

What defects might you expect to find in connection with calcium silicate bricks?

Answer 191

- Calcium silicate brickwpork (unlike clay) usually undergoes an initial irreversible shrinkage on laying (clay bricks expand). If movement control joints are missed or badly spaced diagonal cracking can occur. Thermal/moisture cracking often visible at changes in the sizes of panels e.g. long runs below windows coinciding with short sections between windows. Look out for thin bed cracks and wider cracks to vertical joints. - Its use as a backing to clay brickwork (inner leaf of cavity wall) is likely to cause problems as a result of expansion of the clay bricks and contraction of calcium silicate brick. Do not confuse with subsidence of corrosion of steel frame. - They are smooth, often creamy coloured bricks made from lime, sand and flint. Small particles of flint can sometimes be seen in cut bricks/weathered surfaces. Widespread use in 1960s and 70s, still manufactured and gaining popularity. - Unrestrained thermal expansion - Drying shrinkage higher than clay bricks - Poor resistance to frost when contaminated by chloride (sea water) – not recommended for coastal areas. - Severe cracking if left (often diagonal), which allows water ingress.

Question 192

Why were woodwool slabs used in construction?

Answer 192

- Woodwool slabs were used as a type of temporary shuttering/formwork for pouring in situ concrete

Question 193

What are the associated problems with leaving woodwool slabs in place to form part of the construction?

Answer 193

- Woodwool slabs are porous and have an open matrix decking which makes it an unsuitable permanent shuttering material. - The in situ concrete fines will flow into the voids in the woodwool (honeycombing) leaving the rebar and aggregate unbound. - This presents structural and fire hazards as the concrete is not adequately compacted.

Question 194

What are the implications if woodwool slabs are left in position?

Answer 194

- As the shuttering obscures honeycombing around the soffit and slab, and around the rebar, the extent of the voidage is impossible to gauge. - The voidage may lead to structural or fire issues. - The possibility of corrosion occurring to the rebar, especially in damp conditions is heightened.

Question 195

What remedial options would you advise your client on sighting suspected woodwool shuttering on a survey?

Answer 195

- Where voidage is excessive, the application of a spray gunite is required - The fire resistance can be reinstated by the addition of boarding - A structural engineer’s advice would need to sought.

Question 196

What is Regents Street Disease?

Answer 196

- The corrosion of steel framed buildings owing to poor corrosion protection during the original construction.

Question 197

How would you identify that Regents Street Disease has taken place and what are the factors which influence it?

Answer 197

- Visually, it is only identifiable at the advanced stages where displacement of the façade has occurred owing to the expansion of the steel below. - The rate of corrosion will depend on the orientation of the building, weather and the type and thickness of the façade.

Question 198

How is Regents Street Disease caused?

Answer 198

- Water and oxygen find its way into the structure through degraded mortar joints or faulty degraded surfaces such as cracked rainwater goods. - Close proximity of mortar to steel, the expansion will cause reflective cracking in surface materials.

Question 199

What are the remedial options available for a building with Regents Street Disease?

Answer 199

- The affected areas of the façade have to be removed and replaced following treatment of the steel. - This is expensive and not always practical - If RSD is discovered in its early stages, cathodic protection could be used.

Question 200

What is HAC and where is it commonly used/found?

Answer 200

- High alumina cement can also be known as calcium aluminate cement (CAC) - Commonly used in the 1950s-60s for the production of pre-cast and pre-stressed concrete elements.

Question 201

Why was HAC popular in the 1950s and 60s?

Answer 201

- It has high strength - High temperature and good resistance to sulphate attack - It also cured in 24 hours and not 28 days like Portland cement.

Question 202

How can you identify HAC on site?

Answer 202

- The cement is a light brown/grey colour.

Question 203

What causes HAC to become a defective building component?

Answer 203

- Internal chemical reactions create voids in the cement matrix. - Voids mean a reduction in strength and it becomes more porous. - Porosity can cause corrosion of rebar, which can lead to a failure of the structure - The failure of the structure is brought about by the increase of susceptibility to carbonation, sulphate attack and chloride attack.

Question 204

What are the remedies for buildings suffering from HAC?

Answer 204

``` - A three stage investigation needs to be carried out on buildings suspected to have HAC. o Identification (rapid chemical test) o Strength assessment (sufficient structural capacity) o Durability assessment (determine long term durability where rebar affected by corrosion) ```

Question 205

When was HAC banned?

Answer 205

- 1974

Question 206

What is Mundic concrete?

Answer 206

- Concrete manufactured from quarry shale and is commonly found in the west country for concrete blocks.

Question 207

What are the issues with Mundic concrete?

Answer 207

- Generally a loss of strength in damp conditions - Mundic decay can take place which is where the sulphide minerals in the mine or quarried Mundic rock oxidise under damp conditions and produce sulphuric acid.

Question 208

What is the difference between subsidence and settlement?

Answer 208

- Subsidence is downward foundation movement caused by change in the site below the foundations, usually associated with volumetric changes in the subsoil. It occurs when the soil beneath a building is unstable and sinks downwards. - Settlement is downward foundation movement caused by an application of load, usually occurring for a period of time immediately after construction or poorly compacted ground. It is caused by the weight of the building, but it can still have a negative impact on the overall structural stability.

Question 209

Explain the sequence of work involved in underpinning a strip foundation.

Answer 209

- Prior to commencing, notify adjoining owners (Party Wall etc. Act 1996), undertake an SoC of adjoining owners’ property, install tell-tales to any cracks so subsequent movement can be monitored, undertake a detailed ground survey of the area, remove imposed loads as far as possible and install props as necessary, identity, support and protect services as necessary. - To prevent damage, settlement and fracture, work should be carried out in short lengths (legs or bays). These are generally in lengths of 1-1.5m for mass concrete strip foundations supporting traditional walls, or 1.5-3m for retained concrete strip foundations supporting moderate loadings. - The sequence of bays should be arranged so that working in adjoining bays is avoided until one leg of the underpinning has been completed, pinned and cured sufficiently to support the wall above.

Question 210

What are the different types of ground movement?

Answer 210

- Subsidence - Heave - Settlement - Differential settlement

Question 211

What indicators could you pick from a survey that the property might be suffering from the effects of ground movements?

Answer 211

- Cracks show internally and externally | - Floors slope, walls tilt and door and window openings distort.

Question 212

What is subsidence?

Answer 212

- The downward movement of a building’s foundation caused by the loss of support below the foundation.

Question 213

What are the effects of building on soft clays and silts?

Answer 213

- Soils if this type have very low strength which leads to low bearing capacities.

Question 214

What are the effects of building on sands and gravels?

Answer 214

- Sands and gravels have high permeability and frictional strength with a lack of adhesion. - It may be necessary to consolidate this group of soils if excavations have to take place.

Question 215

What signs would indicate that subsidence has taken place?

Answer 215

- Diagonal cracking which is usually tapered (uneven width wider at the top) in the building’s structure/façade. - Usually affects localised areas of foundations and not all of them as a whole.

Question 216

How is subsidence caused?

Answer 216

- Can occur when excessive water leaks into the soil with a higher gravel/sand content and washes away the foundations - Mining which has sudden effects can be the cause of subsidence depending on the mining method - Can occur on clay soils that shrink when their moisture content decreases due to trees, etc.

Question 217

What remedial measures are available for subsidence?

Answer 217

- Underpinning can be an option, but it is expensive and disruptive - Guidance should be sought from a structural engineer

Question 218

What is heave?

Answer 218

- The mass upward movement of material as a result of expansion

Question 219

How might you identify that heave has taken place?

Answer 219

- There is an expansion at the corner of the building causing lifting through localised clay heave. - Diagonal cracking that tapers (wider at the bottom)

Question 220

What are the typical causes of heave?

Answer 220

- Ultimately it is volume changes in clay soils which are a common cause of subsidence - Felling a tree in the vicinity of the existing building, particularly in clay soils. - Homes built on chalky soil which are unheated and unoccupied can be subject to heave

Question 221

How might you remedy the effects of heave?

Answer 221

- Seek advice of a structural engineer/geotechnical engineer.

Question 222

What is settlement?

Answer 222

- The vertical downward movement of ground due to the imposed loads of the foundations which occurs soon after construction.

Question 223

How might you identify if settlement has taken place?

Answer 223

- Cracks occur at the junction between row elements. - Wide cracks appear at the bottom of the building, often around doors and window openings and narrow cracks appear at the top of the building.

Question 224

How is settlement caused?

Answer 224

- Settlement is caused by pressure which is applied to the sub-soil by a new building - Any water within the subsoil is squeezed out by the new load

Question 225

How might you remedy the effects of settlement?

Answer 225

- If the cracking is above category 2 (5mm) then underpinning is probably required. - The advice of a structural engineer should be sought for cracks over 5mm in width.

Question 226

What is differential settlement?

Answer 226

- Where unequal pressure occurs on the foundations arising from extensions or concentrations of loads e.g. chimneys. - Bay windows with shallower foundations

Question 227

What are the typical defects associated with a Georgian building?

Answer 227

- Unbalanaced butterfly roofs - Parapet gutter blockages with resultant damp ingress - Alterations resulting in dampness, inadequate ventilation, wood boring insects, fungal timber rot. - Defective slates and nail sickness - Degraded chimney pointing - Issues with flashings – often replaced with a cement wedge/tile on edge – recommend lead. - Deterioration of tiles and corrosion to non-galvanised fixings - Rotting lintel adjacent to a bay window roof – can be caused by leaking roof and can cause structural problems - Dampness to solid walls. - Soft red bricks used on walls and are susceptible to damage/deterioration from weather e.g. frost attack, especially if repointed with cement mortar. - Movements to the bays of properties indicating little or no foundations. - Re-pointing/re-painting may have caused the walls to stop being able to breathe, leading to spalling of the brick/stonework. - Rot to sliding sash windows - Improverly formed openings in trussed partitions - Little or no foundations, which can be a problem in clay areas or where there are leaks. - Drainage extended and older installations can cause issues. - Lath and plaster ceiling issues where plasterboard is installed (cracking) - Bouncy timber floors.

Question 228

When was the Georgian era?

Answer 228

- 1714-1837

Question 229

Can you name some key features of Georgian buildings and how might you recognise a Georgian building?

Answer 229

- Square built buildings – symmetry - Roof and gutters are hidden behind a parapet wall - Stucco render to imitate stone - Large sliding sash windows with 6x6 panes of glass that get smaller as they go up the building. - Lower ground floors.

Question 230

What is a butterfly roof?

Answer 230

- A roof which is not easily seen from ground level and features rafters which slope towards the centre of the roof from either side of a party or end of terrace wall. A valley gutter sits in the centre.

Question 231

How might you identify that the butterfly roof is unbalanced?

Answer 231

- The wall next to the roof leans out. | - Often seen at the end of terraces and mono-pitch additions.

Question 232

What is the cause of an unbalanced butterfly rood?

Answer 232

- An unbalanced lateral thrust from rafters leaning against the wall causing creep deflection within the timbers.

Question 233

What is creep deflection?

Answer 233

- Creep in timber members relates to the elastic modulus (sagging) of timber and how stresses affect performance such as moisture content.

Question 234

How would you repair an unbalanced butterfly roof?

Answer 234

- Form a ridged triangle by bolting new posts between existing rafters and joists. - Install straps between wall and ceiling joists at 1200mm centres. - Provide diagonal bracing in the ceiling joists to resist horizontal thrust.

Question 235

How might you identify dampness to solid walls?

Answer 235

- A horizontal tide mark no higher than 1.5m from floor level - Hydroscopic salts brought up from the ground are visible on the tide mark. - Mould and flaking plaster/wallpaper.

Question 236

What are some of the causes of damp to solid walls?

Answer 236

- Georgian houses may have been repointed with Portland cement which encourages penetrating damp and is less porous than lime mortar, so evaporation is restricted. - No DPC or defective DPC causing water to rise from ground level - The height of the water table.

Question 237

What remedial measures would you suggest to cure dampness to solid walls?

Answer 237

- Install a DPC either chemically or physically. - If the property is listed, install a perimeter French drain. - Undertake internal repairs, such as replacing affected plaster and redecorating.

Question 238

What examples can you give of inappropriate openings in Georgian buildings?

Answer 238

- Where the property has been divided into flats and doorways are formed through partitions. - Internal doors have become distorted and the floors sagging are also indicators.

Question 239

What are the effects of creating inappropriate openings in Georgian buildings?

Answer 239

- The diagonal bracing timber members can be severed by installing a new door opening which will lead to the floor sagging or eventual collapse. - If the diagonal members are not severed, the spine wall footings which carry the floor joists and roof structure over large openings may settle and cause cracking.

Question 240

How would you address this problem?

Answer 240

- Remove the doorway and repair the diagonal timber members. - If the doorway must stay, install a beam and provide additional strengthening methods. - If long term settlement is the problem, investigate and undertake repairs to the floor joists.

Question 241

How could you tell if the timber floor is bouncy?

Answer 241

- Dropping the heel of your foot – if the windows and doors rattle and the furniture shakes, the floor is bouncy.

Question 242

Can you tell me what the possible causes are of bouncy timber floors?

Answer 242

- Excessive notching of joists for pipework. | - Herringbone strutting may have been relaxed over time or omitted entirely by new occupiers.

Question 243

What is herringbone strutting?

Answer 243

- Timber that was installed at 1/3 points across joists in a cross position that was tightened with folding wedges. - Modern herringbone strutting is proprietary and can be metal instead of timber.

Question 244

How would you address bouncy timber floors?

Answer 244

- Strengthen the floor by adding extra joists. | - See Approved Document A for guidance, but estimate would be one extra joist for every three which are existing.

Question 245

What are the typical defects associated with a Victorian building?

Answer 245

- Distortion, dishing or sagging to old roof timbers – rot of timber purlns or crumbling brick party walls. - Neglected chimney stacks with weathered bricks, loose pots and poor flashings. - Leaking parapet walls – copings can be loose and rendered sides cracked. - Defective gutters and downpipes causing dampness. - Defective masonry to the walls – stone/brick weathered or cracked as a result of structural movement. Lintel construction often poor and walls are often repointed using cement mortar or are covered with a cement based render (should be lime finish) - Poor sub-floor ventilation – should be good vents in front and rear of the house. - Raised ground levels are a common cause of dampness and should be 150mm below floor levels. - Rot to timber floors – common at ground level due to raised ground levels and poor ventilation. - Dampness to the walls inside. - Removal of lateral support from one terraced house to another (book end effect) - Rotten and paint sealed windows

Question 246

When carrying out a survey of a Victorian house, what potential pathology issues could lead to damp problems in the building?

Answer 246

- Penetrating damp entering into modern non-porous renders and getting trapped. - Leaking gutters and downpipes causing penetrating damp. - Rising damp where external ground levels are raised or where external boundary walls abut the external elevations. - Roof leaks due to degraded flashings or slipped slates. - Reduced ventilation due to double glazed windows. - Often no consideration given to ventilation of sub-floor void when Victorian properties are extended.

Question 247

What action might be necessary to free up sliding sash windows that are sticking?

Answer 247

- Avoid forcing a sash to move because it could cause damage. - Sashes sometimes stick, jam or fail to move fully for various reasons, including: - broken sash cords - paint accumulation, (requiring removal not only from the running surfaces, but also pulleys), - a poorly positioned or distorted bead guiding a sash. - It could be necessary to free weights that are fouled, remove debris impeding their movement in the weight pockets or trim a warped sash to allow it to slide properly. - Rubbing beeswax, candle wax or soap along the sash edges makes opening/closing easier. - Seasonal binding through humidity induced swelling should be tolerated, unless it indicates redecoration is needed.

Question 248

Whilst involved in refurbishing a Victorian house you discover there are bats in the roof. What would you do?

Answer 248

- If works are underway, pause all works on discovery. - Seek advice from Natural England or an ecological consultant. - Undertake a bat survey, including details of roosts, where and what species. - Compile a mitigation plan/method statement detailing any works on site that may impact bats and how they can be mitigated – to be shared with architects and/or building contractors. - Incorporate the bat survey report and mitigation plan/method statement into the planning application. - Apply for planning permission and a Protected Species mitigation licence from Natural England before works commence. - If granted, carry out works with ecologist supervision and other required working methods detailed in the method statement. - Mitigation methods include altering work methods or timings to avoid bats, creating/improving roosts, creating/improving foraging or commuting habitat and monitoring the roost sites after development. - Compliance check to ensure that mitigation is properly being implemented - Monitor the site to check the response of the bat population to the mitigation.

Question 249

Your client’s Victorian building has solid brick external walls. There are a number of diagonal cracks in different parts of the building. What action would you take?

Answer 249

- I would make a note of all the cracks, look at the proximity of trees, lines of drains and establish the soil type. - I would then monitor the cracks and look internally to establish if the cracks are current or historic. - If it is deemed that the cracks are active, and that subsidence is likely, I would recommend that my client consults a structural engineer.

Question 250

What factors would lead you to recommend re-covering a slate pitched roof rather than patch repairing?

Answer 250

- If over 20% of the roof slates are damaged it is worth re-roofing as it would be uneconomical to patch repair the roof.

Question 251

When was the Victorian period?

Answer 251

- 1837-1901

Question 252

What features define a Victorian building?

Answer 252

- Buildings were pointy with steep roofs. - More ornate features, such as corbelling and decorated fascia boards. - Timber window panes were larger (6x4) panes - Ground floor bay window often had its own roof. - Stained glass was used in this period generally above doors and at the tops of windows.

Question 253

Can you list some typical defects which can occur in Victorian buildings?

Answer 253

- Nail sickness to roof slates - Spalled brickwork - Lack of restraint to flank walls - Rotten floor joists and dry rot to ground floors - Deterioration of filler joisted concrete slabs

Question 254

What is nail sickness?

Answer 254

- Numerous slates progressively slipping out of place due to failure of the poor quality galvanised or iron nails

Question 255

What causes nail sickness?

Answer 255

- The nails holding the slates in position corrode due to exposure to the elements resulting in slipped slates.

Question 256

What would you recommend to address a roof suffering from nail sickness?

Answer 256

- Isolated repairs in minor incidents – refix the slates using aluminium or copper fixings. - Replace all of the slates if more than 15% of the roof is suffering from nail sickness.

Question 257

What is spalled brickwork and where might you expect to find an example of it?

Answer 257

- Spalled brickwork is the disintegration of the facing sections of brick. - It can often be seen on exposed elevations such as parapets, close to the ground and near water runoff points.

Question 258

What are the causes of spalled brickwork?

Answer 258

- It can occur in older bricks and those under burnt during firing. - It occurs near the surface of the bricks as moisture gains easy access. - Frost attack then takes place which requires regular freeze and thaw cycles when the material is wet. The expansion caused by the freezing of the trapped water causes the brick to break/spall off.

Question 259

How would you remedy sections of spalled brickwork?

Answer 259

- Remove the source of wetting i.e. repair leaking rainwater goods - Cut out and replace the defective sections of brick in isolated locations.

Question 260

What are the symptoms of a lack of restraint to flank walls and what other term is used to describe this defect?

Answer 260

- The ‘book end effect’ - Leaning flank and party walls. - Vertical cracks in the front and rear elevations - Gaps appearing between floor and party walls.

Question 261

What are the causes of book end effect?

Answer 261

- Lack of movement joints in terraces. - Contraction near walls at window openings. - Brick fragments fall into the cracks and prevent closure on expansion - After cyclical movement the flank and party walls are pushed further away so that they are out of plumb.

Question 262

Why are expansion joints needed in long sections of brickwork?

Answer 262

- They allow thermal movement and moisture movement to take place (expansion and contraction).

Question 263

What would you recommend to address a Victorian building suffering from the book end effect?

Answer 263

- Cut movement joints into long sections of brickwork terrace walls at 12-15m centres - Undertake repairs to the cracks, windows, etc. as required.

Question 264

What are the symptoms to dry rot to timber ground floors?

Answer 264

- Timber joists become dry and crumbly, lightweight with a light brown colour. - Deep cuboidal cracking appears on the timber. - Mycelium appears along with a musty smell and yellow staining to the timber. - Spores appear like a fine layer of red dust over the timber and substructure brickwork. - The fruiting body is pancake shaped with a white margin.

Question 265

What are the causes of dry rot to timber ground floors?b

Answer 265

- Timber with a moisture content between 17-22% susceptible to dry rot - Blocked air vents and no DPC are the most common causes

Question 266

How would you remedy an outbreak of dry rot in a Victorian property?

Answer 266

- Eliminate the source of moisture and promote rapid drying - Remove all rotten wood and up to 450mm of sound, adjacent wood - Treat all surrounding timber and brickwork with a preservative - Splice in and install new treated timbers and coat with a preservative - Improve the ventilation pathways if possible.

Question 267

What are filler joisted concrete slabs and what are the signs of its deterioration?

Answer 267

- Clinker concrete was used in the Victorian period. | - Straight cracks in soffits and at regular intervals across the ceiling indicates steel filler joists.

Question 268

What is the cause of the deterioration (filler joisted concrete slabs)?

Answer 268

- When clinker concrete is wet, it draws out acids from the incumbent coal in the clinker concrete, which corrodes the steel filler joists. - Steel expands when corroded and the expansion pushes the concrete cover off and forces the slabs apart.

Question 269

How would you address the deterioration of filler joisted concrete slabs?

Answer 269

- Replace any corroded sections or the entire beam if necessary and make good. - All water ingress should be stopped and the expanded steel treated to prevent further corrosion with a Sika product.

Question 270

What defects are common to Victorian and Georgian buildings?

Answer 270

- Sulphate attack of mortar - Partially removed chimney breasts - Rotten joist ends

Question 271

How would you identify if sulphate attack had occurred in mortar?

Answer 271

- Bulging walls - Distorted chimney stacks - Cracked/loose mortar - Friable mortar joints and loss of bond

Question 272

Can you tell me what causes sulphate attack?

Answer 272

- In superstructure brickwork, driving rain/moisture which has become trapped in render saturates the clay bricks and transports soluble sulphates from brick to mortar - In substructure brickwork sulphates can form from ground water movement and through capillary action, enter the brickwork and cause damage by expansion of the mortar and distortion of the wall.

Question 273

How would you remedy sulphate attack?

Answer 273

- Eliminate the source of water and replace the affected bricks where necessary - Where the wall cannot be prevented from being wetter, say an elevation wall, and the bricks have a high sulphate content, demolish the wall and rebuild with sulphate resistant bricks and mortar.

Question 274

Name three protected species other than bats?

Answer 274

- Dormice - Great crested newts - Breeding birds including barn owls - Badgers

Question 275

Where would you go to find out if a species is protected?

Answer 275

- DEFRA (Department for Environment, Food and Rural Affairs), Natural England or the Environment Agency

Question 276

Is it only animal species that are protected?

Answer 276

- Trees can be protected by a Tree Preservation Order.

Question 277

What is Radon and in which areas of the UK are you most likely to come across it?

Answer 277

- Radon is a colourless, odourless, tasteless naturally occurring radioactive gas produced from the radioactive decay of uranium found in all rocks and soils. It escapes from the ground into the air, where is decays and produces further radioactive particles, with concentrations higher indoors and with areas of minimal ventilations. - It enters buildings through cracks in the floors or at floor-wall junctions, gaps around pipes or cables, small pores in hollow block walls, cavity walls, sumps or drains. Concentrations generally higher in basements. - It can occur in any region of the UK, but is most prominent in Wales and the South West of England. - It is one of the leading causes of lung cancer - Reducing it can be done by increasing under-floor ventilation, installing a radon sump system in the basement or under a solid floor, sealing walls and floors with a polythene impermeable gas barrier/radon barrier

Question 278

Give an example of an interesting pathology issue that you have had to deal with.

Answer 278

- During a dilapidations assessment of a boarding school in Sussex I identified low level tide marks, discolouration and mould to the external walls, damage to the timber skirtings and doors, and staining and mould to the carpets. I reviewed the external elevations and established that the damp proof course had been breached by a tarmacadam path and that loose shingles had blocked a number of ventilation bricks. - I notified my client of the disrepair and recommended that the tarmacadam path be redesigned to ensure that external ground levels are lower than the dpc and that the ventilation bricks were cleared of all loose shingles. Replace all damaged plaster internally. - Perimeter drain, insert a new DPC if these methods do not resolve the issue (physical or chemical insertion)

Question 279

What other methods could you have used to confirm whether it was rising damp and the level of dampness?

Answer 279

- Electrical resistance method – easy to use, rapid results, non-destructive, pinpoints damp contours up to 1.5m, readings should drop quickly above peak dampness, high MC in timber skirtings, high readings at base of wall and gradually reducing higher up. Usually calibrated to timber and calculations are needed for use in brick/plaster. It only reads surface moisture (unless deep probes are used) and naturally occurring soluble salts give false positive readings and foil backed plaster can give 100% relative reading. Best use is as a comparison to see changes over time. - Drilling techniques – generally used on masonry – need a standard percussion drill and device to catch the drill dust. Weigh it in a lab, dry it and weigh it again to calculate the moisture content. Samples through the depth of the wall. - Calcium carbide test – variation of drilling, but provides a quick and relatively accurate on-site determination of MC. Samples are inserted with calcium carbide into a pressurised vessel to provide almost an instant reading. - Removable cores and samples – cylindrical core cutter used. Goes to lab where it is sliced up and weighed, reinserted back into the wall and left for a period of time, when it can be re-tested. Sophisticated but accurate method - Environmental monitoring – installing sensors which relay measured data on moisture, temperature, relative humidity and air movement. High cost.

Question 280

How would you determine if a drainage run was free from breaks or blockages?

Answer 280

- Visual inspection of the surrounding ground levels to see if there are any uneven surfaces. - Review the drain inspection covers to see if it is full or empty of water to determine where blockages are. - Undertake a CCTV drainage survey.

Question 281

What steps would you need to take if your client wanted to build in an area where Radon gas was present?

Answer 281

- Tank the basement and use a sump system to ensure the radon is emitted from the property.

Question 282

Can you name some invasive weeds?

Answer 282

- Japanese Knotweed - Giant Hogweed - Himalayan Balsam - Ragweed

Question 283

How do you identify Japanese Knotweed?

Answer 283

- Forms in dense clumps up to 3m tall - During the spring it presents red tinged leaves and in summer, purple with green specs. - Often found near railways, riverbanks and derelict sites. - Stem is bamboo like and the rhizomes are thick and orange internally.

Question 284

What is a rhizome in relation to Japanese Knotweed?

Answer 284

- An underground stem system that can spread 7m in any direction - Internally it is generally orange, but can be white when young.

Question 285

What are the implications of the discovery of Japanese Knotweed?

Answer 285

- Native plants and birds, insects and mammals suffer. - Its presence reduces land value - As the roots can grow 7m in length, it can grow through manmade structures, penetrating floor slabs, drainage runs etc.

Question 286

What Act governs the disposal of Japanese Knotweed?

Answer 286

- Wildlife and Countryside Act 1981.

Question 287

What remedial actions are available to your client when considering dealing with Japanese Knotweed?

Answer 287

- Excavation - Root barrier - Herbicide control

Question 288

Explain the excavation of Japanese Knotweed.

Answer 288

- Dig a large hole of no prescribed dimensions ensuring that the rhizomes are chased out - The risk with this method is that even a tiny fragment of the plant is enough for it to grow again.

Question 289

What can you do with the waste following removal of Japanese Knotweed?

Answer 289

- Bury the waste at source - Bury the waste at an authorised landfill site (contact the Environment Agency and the landfill site in advance) - Burn it

Question 290

What must you do when you intend to bury Japanese Knotweed waste at source?

Answer 290

- Check with the Environment Agency - Bury the waste to a depth of at least 5m. - Cover the remains with a root barrier membrane so that it does not allow the plant to grow. - Where 5m is not possible to dig to, the waste should be wrapped completely in a root barrier membrane and dug to a depth of 2m.

Question 290

What must you do when you intend to bury Japanese Knotweed waste at source?

Answer 290

- Check with the Environment Agency - Bury the waste to a depth of at least 5m. - Cover the remains with a root barrier membrane so that it does not allow the plant to grow. - Where 5m is not possible to dig to, the waste should be wrapped completely in a root barrier membrane and dug to a depth of 2m.

Question 291

Tell me about burning Japanese Knotweed waste on site.

Answer 291

- Farmers can burn the waste on site, but they must tell the Environment Agency at least one week before and their local environmental health officer. - As an individual you can burn on site once you have checked with the local council that burning is allowed. - The waste can survive burning so you will then need to dispose of that waste.

Question 292

How do herbicides work when treating Japanese Knotweed?

Answer 292

- Regular spray application of approved chemicals over 3-4 growing seasons to gradually kill off the plant. - The underground rhizomes will not disappear, but will become dormant. - Mechanical disturbance is often used to shorten the programme as each section is broken up.

Question 293

What must you when using chemicals on Japanese Knotweed?

Answer 293

- Make sure that anyone spraying holds a certificate of competence for herbicide use or works under the direct supervision of a certificate holder. - Carry out a COSHH assessment - Get permission from Natural England if the site is protected - Get permission from the EA if plants are near water - Must dispose of all chemicals when complete through a registered waste carrier to a permitted disposal facility.

Question 294

What regulations govern the use of pesticides?

Answer 294

- Control of Pesticides Regulation 1986

Question 295

What is giant hogweed and where might you find it?

Answer 295

- Introduced to Britain in the 1800s as an ornamental plant - Riverbanks - Roads - Railways - Wasteland

Question 296

How might you identify giant hogweed?

Answer 296

- In spring and summer it can grow up to 5m tall and has an umbrella shaped white flower head - The thick stem has sharp bristles with purple spots - In winter the stem is cream and bamboo like.

Question 297

What are the key differences between hogweed and giant hogweed?

Answer 297

- Height - Width of the stem - Size of the leaf - Size of the flower head - Size of seed - All of the above are smaller with hogweed

Question 298

How does giant hogweed spread?

Answer 298

- Relies solely on reproduction by seed, not fragments of itself as Japanese Knotweed. - It takes 2-5 years to flower and die - Wind carrying the seeds is the primary means of spreading with accidental dispersion by humans along roads and pathways.

Question 299

What are the impacts of giant hogweed?

Answer 299

- Dangerous to human health - Red rash and blistering within 24-28 hours of contact - Humans often unaware of touching leaves and becoming affected as it is painless

Question 300

What are the different methods and removal strategies of giant hogweed?

Answer 300

- Seed head removal - Hand pulling - Herbicide treatment - Excavation and disposal to landfill.

Question 301

Why might you just remove the seed heads of a giant hogweed?

Answer 301

- Stops further contribution to seed bank - Helps prevent new growth - Takes between 3-5 years to be effective - The downside is that it does not control the adult plants - Seed heads should be disposed of at controlled waste sites.

Question 302

Why might you use hand pulling to manage giant hogweed?

Answer 302

- For small strands in sensitive areas where seed bank is being controlled - Prevents damage to other species and wildlife - The operator should wear full protective clothing to prevent blistering occurring to skin.

Question 303

How long would you expect concrete tiles to last for?

Answer 303

- 65 years

Question 304

How long would you expect steel to a pitched roof to last for?

Answer 304

- 40 years

Question 305

How long would render typically last on a masonry wall?

Answer 305

- 50 years

Question 306

How long would you expect reinforced concrete to last for upper floor construction?

Answer 306

- 80 years

Question 307

How long would you expect pre-cast concrete to last for upper floor construction?

Answer 307

- 70 years

Question 308

How long would you expect boilers to last for?

Answer 308

- 20 years

Question 309

How long would you expect air conditioning units last for?

Answer 309

- 15 years