Building Pathology Flashcards

Question

Where does wet rot grow?

Answer 1

Wet rot fungus occurs when there is excess moisture in the property. This rot needs a continuous source of moisture to germinate and thrive, as a result, wet rot will only affect internal timber if there is a significant damp problem. Common property maintenance issues like structural defects, broken plumbing or guttering and leaking pipes can leading to rotten wood, timber decay and wet rot fungal growth. Wet rot will grow on wood with a moisture content of between 30-60%. Wet Rot thrives in timber with a high moisture content of around 50% or higher, whereas dry rot only requires 20% moisture presence before it can attack. This is usually caused by defects in plumbing, external guttering or pipework that create leaks. Wet rot thrives when these damp conditions combine with a lack of adequate ventilation. A challenge associated with identifying wet rot is that it often develops in hard-to-spot areas of a property due to unseen water ingress. As a result, wet rot can be commonly found in damp basements, under floorboards, behind skirting boards and underneath leaking fixtures and fittings such as baths, toilets and washing machines.

Answer 2

- remove the source of moisture. Leaks, sub-floor ventilation. - remove affected timber where necessary (weakened). Use a pre-treated timber for any repairs. - apply a fungicide

Answer 3

Group of fungi called Poria Fungi. These fungi generally attack softwood in buildings. They require a higher moisture content in the wood than that required by dry rot, but they are tolerant of occasional drying and are therefore normally associated with roof leaks. This group includes Amyloporia xantha, Fibroporia vaillantii and Poria placenta. They are commonly called white pore fungi or mine fungi. F. vaillantii can cause extensive damage in buildings. The mycelium of this group of fungi forms white or cream sheets or fem-like growths, which may discolour brown on contact with iron. The rhizomorphs may be up to 3 mm in diameter, seldom thicker than twine, white to cream in colour, remaining flexible when dry, and they do not extend from their foci of infection. The sporophore is rare in buildings; it is a white, irregular lumpy sheet 1.5- 12 mm thick, covered with distinct pores, sometimes with strands emerging from its margins. Spore-bearing surfaces are white to pale yellow, occasionally with pink patches (P. placenta only). The decay damage to wood is similar to that caused by S. lacrymans, but the cubing is somewhat smaller, less deep and lighter in colour. When decayed, the wood crumbles between the fingers. It is not as powdery as that attacked by S. lacrymans, but slightly more fibrous and gritty.

Answer 4

Settlement or differential movement.

Answer 5

If a tree is removed, the moisture returns to the soil slowly causing it to expand (heave) by as much as 150 mm. Because the effect of the tree is localised, the movements generated in nearby foundations are differential and can be much more damaging than uniform movements. Tree roots can extract large quantities of water from soil: a fully grown poplar uses over 50,000 litres in a year. When the soil is of clay, this will lead to a drying shrinkage, the magnitude of which will depend upon the inherent properties of the clay and, of course, on the nature of the tree and its moisture requirements. If tree roots take up moisture from under, or near to, foundations, the latter will subside and such subsidence will almost inevitably be uneven The greatest problems have occurred when shrinkable soils have dried excessively through the removal of moisture by nearby growing vegetation. Such drying is likely to be greatest at the corners of foundations. As the ground falls away, the weight of the building pushes the then suspended parts of the foundations down and the walls in that vicinity crack. Cracking is predominantly diagonal and follows the vertical and horizontal mortar joints in brickwork, unless the mortar is abnormally strong for the bricks used, when cracking may occur through the latter. The cracks are widest at the top corners of the building and decrease as they approach ground level.

Answer 6

Electronic damp meter (moisture meter) Speedy carbide meter

Answer 7

Meters are only calibrated for timber, Hygroscopic salts can exaggerate reading (it is important to test for salts), Different species of timber have different resistances, The following can provide exaggerate readings; - Copper, Chrome or Arsenic treated timber - Foil lined wallpaper - lead paint

Answer 8

A calcium carbide meter is a sealed vessel which is used to mix measured samples of masonry with calcium carbide. The calcium carbide will react with moisture present within the material and produce acetylene gas. The proportion of gas released is directly proportionate to the amount of moisture present in the material, therefore by measuring the gas, we can derive the total moisture content of the sample tested. The flask incorporates a calibrated gauge which is used to measure the pressure excreted in the cylinder by the gas which is read as a moisture content percentage.

Answer 9

Damp meters usually work by measuring the electrical resistance between two pins. Often displaying the moisture content as a percentage.

Answer 10

Destructive technique Generally not as quick as other methods.

Answer 11

Crack width gauge, Plastic tell tale, Glass tell tale, Brass screws and callipers, Target and total station

Answer 12

BRE 251 - categorising cracks and determining where intervention is necessary BRE 292 - Cracking in buildings. BRE 343 - measuring and monitoring BRE 361 - why do buildings crack

Answer 13

Observing crack width changes is one technique used to monitor structural damage due to movement. BRE 343 gives guidance on measuring and monitoring cracking in low-rise buildings.

Answer 14

Steel ruler is simple instrument used to monitor crack width variation. The crack can be measured to the nearest 0.5mm. Typically used at the start of a crack investigation.

Answer 15

The plate with scales marked in millimetre units of measurement is fixed on one side of the crack and the other plate marked with cursor is fixed on opposite side of the crack. Pros include; They can measure cracks along two axis, can get corner crack monitors. Cons include; fixings can come loose especially if stuck on with adhesive or if knocked. Typically 1.0mm degree of accuracy.

Answer 16

This technique used to measure crack width variation in the past, but it is not popular any more. It basically consists of strip of glass cemented on to the cracked structural element. This method is no longer used because there is no way of measuring the extent of the movement or direction.

Answer 17

In this technique of monitoring crack width variation, two screws are fixed on each side of the crack at 90 degrees. The screws will guarantee the correct measurement of the crack width and prevent errors. Digital callipers often have a resolution of 0.01mm. In some cases discs are glued onto the wall.

Answer 18

Longhorn beetle, Deathwatch beetle, Powderpost beatle, Common furniture beetle, Wood boring weevil.

Answer 19

Egg - Laid in or on the surface of the wood Lava - 4 weeks to years feeds within the wood Pupa - 1-4 weeks+ lava is nearlly fully grown and begins to surface Adult - 1-35 days fully grown mates and lays eggs

Answer 20

Flight holes, Frass, Damp timber,

Answer 21

Flight hole are where the lava emerge from affected timber. Typically sized 1-3mm, can help identify the type of insect e.g. longhorn beetles have flight holes between 6-9mm. Typically round, the shape can help identify the type of insect e.g. weevils create jagged holes, Longhorn beetles create oval holes.

Answer 22

Location some insects are exclusive to a region or country e.g. termites are not found in Northern Europe, Longhorn beetles are restricted to Surrey. Types of timber certain types of insect prefer certain types of timber. Some only attack soft wood or hardwood e.g. Powderpost beetle. Some attack only rotten timber e.g. weevils. Some only attack sapwood.

Answer 23

The application of insecticide is usually sufficient to eradicate woodworm. Application of a liquid formulation to the surface of affected timbers by brush or typically low pressure spraying of permethrin, cypermethrin and cyfluthrin. Bat friendly gels and pastes are available. Remove damp affected timber.

Answer 24

The is an RICS guidance note on mundic entitled - the mundi problem, 3rd edition. Blocks produced from waste rock worked from mining, quarrying and beach gravel. The production of the blocks using these materials took place from the turn of the twentieth century until the 1950s. The blocks produced from waste rock worked from mining, quarrying and free supplies of beach gravel. The mine waste rock was a coarse aggregate with fine mix aggregates produced from beach sand, china clay waste or mine processing residue. In the early part of the 20th century, before standards were laid down for the quality of aggregates in concrete, it appears that many builders were making their own blocks and mass concrete from readily available aggregates. The blocks breakdown overtime and leads to problems with the structural integrity of the property due to a weakening of load-bearing and non-load-bearing walls. The blocks typically degrade from the inside of the cavity to the surface.

Answer 25

The RICS guidance note on mundic entitled - the mundic problem, 3rd edition, discusses the classification of samples. A1 - Sound concrete in satisfactory condition A2 - Concrete considered sound subject to adequate protection and maintenance. They contain up to 30% of Group 2 aggregate types, except in the case of footings. A3 - Stage 3 expansion tested containing less than 30% possible problem aggregates. B - Contains more than 30% possible problem aggregates (group 2 aggregates) although appears sound C - Clearly unsound from initial examination or following detailed petrographic tests. Typically and according to the mundic problem 3rd edition (RICS professional guidance), options A1-3 are mortgageable, B-C are not.

Answer 26

The RICS guidance note on mundic entitled - the mundi problem, 3rd edition discusses the petrographic examination procedure, interpretation and classification. Routine testing is taken in a 15km radius of Tavistock and much of Cornwall. See mapping. Testing recommended if the property displays any evidence of mundic-related deterioration. A number of 50 mm diameter drill holes where a “core” is taken from the external walls, samples of foundations and, where accessible, internal walls and the chimney. Stage 1 - Initial visual assessment. Samples are examined “as received" and then cleaned and then examined again when wet. Many samples can be classified as Class A or Class C at this stage. The examination involves visual assessment, with an aided eye, low power magnifiers or where appropriate, medium power microscopes. Stage 2 - Stage 2 consists of microscopical visual examination and/or analysis through - Examination of thin-section, Examination of polished surface, Chemical analysis and Cement content analysis, for mass concrete footings only when appropriate. The petrographic examination of a thin section is the most common Stage 2 examination on a concrete sample that cannot be classified in stage 1. Thin section examination will allow reliable identification and quantification of aggregates, including those potentially deleterious. It will also allow assessment of the condition of the concrete. Stage 3 - Normally, properties built with Class B concrete are considered unmortgageable. The Stage 3 moisture sensitivity test aims to indicate the performance of the concrete regardless of its aggregate type. It is only applicable to Class B concretes (and, in exceptional circumstances, possibly A2 and formerly A/B concretes) that show no obvious evidence of aggregate-related or other degradation. For Class B concretes (containing group 2 aggregate, but otherwise sound), following Stage 1 and Stage 2 test procedures. Relatively expense and time consuming and unsuitable for some types of aggregates, the supervising surveyor should ensure that Stage 3 is required and appropriate.

Answer 27

- Coarse and fine aggregates. Size, grading, shape, colour, density. Preliminary identification of composition (if possible), any evidence of aggregate reaction, including iron oxide staining or mineral deposits, any evidence of aggregate cracking and or delamination in fine-grained metasediments. - Sulphide minerals. Note presence or absence of visible sulphide minerals and, if possible, a preliminary identification of composition, estimate abundance, any evidence of aggregate reaction, including iron oxide staining. - Cement matrix. Colour, colour variations, relative hardness, proportion (porous building blocks or more typical concrete). - Distribution of constituents. Uniformity of distribution, any evidence of cement ‘balling’, poor mixing or segregation. - Any evidence of secondary mineral deposits, exudations or efflorescence. - Physical coherence. Any visual evidence and occurrence of incoherence.

Answer 28

Group 1 aggregates (both coarse or fine) are considered 'sound' and not deleterious. There and six (1.1 - 1.6) categories (as per the mundic problem, 3rd edition). Some examples include (name 2) - 1-1. China clay waste 1-2. Crushed granite and related igneous rocks 1-3. Crushed basic and metabasic igneous rocks. 1-4. Furnace clinker or coking breeze 1-5. Beach or river sands and gravels. 1-6. Others (eg Group 2, reclassified as a result of further investigation).

Answer 29

Group 2 aggregates (both coarse or fine) are considered potentially deleterious. There are three (2.1 - 2.3) categories (as per the mundic problem, 3rd edition). Some examples include (name 2) - 2-1. Crushed sedimentary or metasedimentary rocks ('killas'). 2-2. Most metalliferous mining and processing wastes. 2-3. Slags (largely non-ferrous) and incinerator waste.

Answer 30

Reinforced autoclaved concrete planks. BRE issued an Information paper on planks designed before 1980 following the collapse of a collapse in 2018. Planks now past their expected service life and it is recommended that consideration is given to their replacement. Differs from normal concrete as it does not contain course aggregate and is made in factories suing fine aggregate, chemicals to create gas bubbles and heat to cure the compound. Relatively weak and has a quite low capacity for developing a bond with embedded reinforcement.

Answer 31

- Rusting of embedded reinforcement leading to cracking a spalling of the AAC cover. - Cracking, of varying degrees of severity, thought to be associated with moisture and temperature related movement to planks. - Excessive deflection (causing ponding and water ingress and corrosion of reinforcement) - Ponding of rainwater increasing the imposed load - Additional loading due to insulation increases. - Shear failure due to positioning (not extend far enough to hold weight of the plank) of reinforcement within the planks. The transverse reinforcement must be over the bearing (support) below. Bearing sizing very important.

Answer 32

Conduct a risk assessment, Consider the long term plan for the RAAC roof, Check with maintenance staff, facilities managers, contractors and those who have access to the building, Ensure that staff know to report any leaks, cracks or other potential defects.

Answer 33

Cracking a symptom / sign of various defects. Both after and before hardening defects in concrete. - Corrosion of reinforcement (though leaching, carbonation, or chloride-induced corrosion). - Inherent defects / design (RAAC, no-fines, under-design or changes in loading) - Alkali-silica reaction - Freeze thaw, temperature variations.

Answer 34

Alkali-Silica Reaction (ASR) commonly known as ‘concrete cancer’ is the most common form of alkali-aggregate reaction (AAR). ASR occurs when moisture (pore fluid) reacts with some types of aggregates (siliceous minerals) which produces a hygroscopic gel that expands. The expansion causes craze cracking. Or parallel to any reinforcement.

Answer 35

Critical level of silica in the aggregate e.g. chert & quartz Sufficient moisture content High Alkalinity content from cement or external sources

Answer 36

Use of low alkalinity cements such as portland-pozzolan cement Control access to moisture and alkali from external sources. Use proven non-reactive aggregates Use concrete mixes with a low w/c ratio Use low cement concrete. Less cement provides less alkali to the system

Answer 37

Subsidence is the sudden sinking or gradual downward settling of the ground’s surface with little or no horizontal motion.

Answer 38

Opening and closing of cracks on a seasonal basis. External cracking in the same location as the internal cracking, Cracks tapering in width between the top and bottom. Cracking occurring around weak structural points, such as doors and windows.

Answer 39

Absorption of moisture by trees and shrubs which can cause the water content of the ground to fall. Collapsing drains, culverts, hidden mine shafts, e.t.c Buried organic material being which decomposes and destabilises all or part of a building’s foundations. Improperly compacted ground. Sand or silt-based soils losing their water-soluble plant nutrients, in a process known as leaching.

Answer 40

Tree Roots - Tree Root Barriers made of high-density polyethylene can be a quick and cost-effective preventative method. In some cases, the removal of a tree can reduce the likelihood of subsidence Underpinning - Underpinning the foundations usually prevents further movement. It’s a lengthy, costly and disruptive procedure that can cost anywhere between £5 000 and £50 000 or more. a structural engineer should be consulted. Pipework - repairs to leaks to pipework will in some cases be enough to stabilize the property without underpinning. Soil rehydration - can be used to induce an early recovery of the building and closure of cracks from clay shrinkage subsidence, allowing repairs to proceed.

Answer 41

Carbon dioxide from the atmosphere permeates the concrete surface and may eventually reduce the alkalinity of the concrete surrounding the reinforcement allowing corrosion of steel in moist or wet environments. Carbonation is the reaction of carbon dioxide in the environment with the calcium hydroxide in the cement paste. This reaction produces calcium carbonate and lowers the pH to around 9. A carbonation front is established which progresses from the outer surface of the concrete inward, resulting in a loss of protection to steel where reinforcement is in contact with carbonated concrete.

Answer 42

The phenolphthalein indicator solution is applied to a fresh fracture surface of the concrete. If the indicator turns purple, the pH is above 8.6. Where the solution remains colourless, the pH of the concrete is below 8.6, suggesting carbonation.

Answer 43

Rust staining or exposed rebar often with poor cover. Buildings built in the 50s and 60’s had less than 10mm of cover in places. Surface cracking at rebar locations. Spalling of the concrete surface.

Answer 44

The reinforced bar must be descaled and cleaned ready for an anti-corrosion coat to be applied. This coat isolates the bar and protects it from water and chemicals that could cause further corrosion. Next the missing concrete needs to replaced; if a higher cement to water ratio is used then carbonation will be a slower process. Once the repair mortar is set then an anti-carbonation coating can be applied to prevent carbonation of the concrete.

Answer 45

HAC concrete in the UK is discussed in BRE Special digest SD3. High Alumina Cement (HAC), sometimes known as calcium aluminate cement (CAC) or aluminous cement, is composed of calcium aluminates, unlike Portland cement which is composed of calcium silicates. It is manufactured from limestone or chalk and bauxite. It became popular in the 1950s, 60s and 70s, as it developed strength rapidly and so was relatively fast to manufacture. It was widely used in structural concrete such as pre-cast beams. However, HAC was prone to a crystalline re-arrangement (or ‘conversion’), which could result in reduced strength, increased porosity and vulnerability to chemical attack when exposed to water for long periods.

Answer 46

Usually, HAC is a darker darker colour than ordinary Portland cement concrete. To conclusively identify HAC optical petrography or testing is required. Rapid chemical tests are available, as well as differential thermal analysis and differential scanning calorimetry.

Answer 47

A contaminant in glass. Following heating in the tempering process the contaminant will change structure, and overtime it will slowly convert back to this structure and increase in size, causing mechanical stress and may cause the pane to shatter for no apparent reason. - In a batch of glass, contaminants that contain nickel might be present, (e.g. stainless steel.) These can combine with sulphur to form nickel sulphide inclusions. Furnaces produce hundreds of tons of glass every day, so it is difficult to eliminate all contaminants. This causes a problem later in the manufacturing process. The process of tempering float glass can cause a NiS to change from its normal state (known as a low-temperature structure) to a different high-temperature, crystalline structure. When the glass is cooled quickly (as part of the process) the NiS particle is unable to change back to its original form. Over a certain period of time NiS will slowly convert to the original low temperature structure. This means the NiS increases in size, and the mechanical stresses caused by this cause the tempered pane to shatter, for no apparent reason (hence spontaneous glass breakage).

Answer 48

Ground heave is the upward movement of the ground usually associated with the expansion of clay soils which swell when wet.

Answer 49

Change in the level of the water table. Broken drains or nearby building works that interfere with existing ground drainage. Swelling of the sub-soils due to seasonal weather changes. Freezing of silty and sandy clays can be more susceptible. Soil being removed from an excavation and so relieving pressure on layers below.

Answer 50

Vertical cracking to brickwork and windows. Doors sticking as their frames become out of square. Lifting of paths and patios surrounding buildings.

Answer 51

Cellular structures such as a cellular raft foundation may be installed beneath foundations and floor slabs to reduce the upward force of heave from transmitting to the structure above. Underpinning may be necessary to stabilise structures. Excavated soil from beneath existing foundations is replaced with material, usually concrete. Remedial works such as repairing leaking drains or removing vegetation may resolve the problem.

Answer 52

Sick building syndrome (SBS) is the term given to symptoms of acute health and/or comfort effects for which no specific cause can be found but that can be attributed to time spent in a particular building.

Answer 53

The Health and Safety Executive (HSE) has compiled recommendations for employers about how to investigate the possible causes of sick building syndrome; Look for the obvious Check the symptoms Ask the staff what the problems are Check procedures and working practices

Answer 54

Since awareness of SBS developed in the 1970s, researchers have tried to pinpoint the precise causes, however, no one single cause has been identified. The most common risk factors believed to contribute to SBS include: Inadequate ventilation. Low humidity, Fluctuations in room temperature. Inadequate sound insulation High levels of noise created by piping M&E Airborne particles such as dust Airborne chemical pollutants Poor lighting.

Answer 55

Most building materials will expand with rises in temperature caused by solar heat gains. In many solid materials, the expansion will usually be greater along the long dimension of the material as opposed to the short

Answer 56

Oversailing of DPC Buckling or bowing of walls Fracture of the masonry units Fracture of an outer leaf of a cavity wall with no joints

Answer 57

Approved document C requires that, to prevent rising damp, a damp-proof course should be: - Continuous with any damp-proof membrane in the floor. - At least 150 mm above the level of the adjoining ground if it is in an external wall. - If it is in an external cavity wall, the cavity should extend at least 225 mm below the damp-proof course, or a cavity tray should be provided with weep holes every 900 mm so that water running down the cavity cannot pass to the inner leaf.

Answer 58

- DPC across the cavity instead of a cavity tray - Missing DPC at corners where the cavity trays meet - Raised ground level above DPC - Rendered over the DPC (abridging) - Inadequate laps of DPCs can also lead to moisture penetration. Laps should be at least 100mm and the DPC laid on a full mortar bed and also fully covered with mortar above to prevent damage. - Bridging of the cavity wall by mortar droppings at the bottom of the wall is more common in new build construction. Leads to irregular damp patches adjacent to the mortar droppings.

Answer 59

Slate (historic) Membrane Engineering brick

Answer 60

Cavity walls have been used since the late 1880s, however was not common practice until the 1940s. There are many types of wall tie; Mild Steel - Pre 1978 with a life span of 15-20 years typically fishtail in shape, flat with a central twist Stainless steel - Post 1980s - typically butterfly shape wire with a central twist up to 75mm or fishtail in shape, flat with a central twist up to 150mm Partial fill wall ties - all types but containing a central plastic disc to hold insulation Proprietary ties - helical wall ties drilled into position fixed by resin Basalt Fibre Wall Ties - A low conductivity rod to reduce thermal bridging with a drip disc at it's midpoint Anchon Channels - Typically used for tying an outer face of masonry to a non masonry Structure.

Answer 61

- Horizontal cracking at regular intervals at external mortar joints. Rust occupies a greater volume of space than the original metal. As corrosion develops, brittle iron oxide layers bulk up the steel strips. Fishtail ties can expand to several times the thickness of the original steel. When repeated along an entire row of steel strip ties, this expansion can create powerful forces that combine to lift and split the wall. The lifting causes a series of horizontal cracks along the hosting mortar beds. Will be first seen at higher levels due to less weight present above. - Outward bulging of walls - The lifting of roof edges at gables. "Pagoda" effect. - Regular spot staining through cracked render - Internal cracking, particularly at wall and ceiling junctions

Answer 62

- BRE in a paper noted that all steel or iron wall ties installed before 1981 are at risk of premature failure. - Aggressive chemicals such as black ash mortar to give it a black colouring. creates a weak sulphuric acid which attacks the galvanised coating. - Chloride salts, which may come from marine sands or may have been added to mortar as accelerators speed up corrosion. - High levels of moisture ingress - Wall ties can be inserted the wrong way around causing water to track through to the inner leaf

Answer 63

BRE Digest 329 gives guidance on installing new wall ties in existing construction It details how to address wall tie failure in varying states - a decision tree is also provided. BRE 401 also details assessment of the current condition of wall ties and choosing a remedial wall tie. If any of the outer leaf is bowed or unsounds it will require rebuilding.

Answer 64

- BS 5628 Part 3 calls for any mortar which unavoidably falls on the wall ties and cavity trays to be removed daily. These can bridge the cavity. Damp patches are likely to occur sporadically and the use of a metal detector will, most probably, indicate that a tie is close by. Mortar droppings creating cold bridge. - Incorrect spacing - generally should be at max every 900mm horizontally and very 450mm vertically. Closer at top of gable walls, around openings and movement joints. - Tie should also extend at least 50mm (embedment depth) into each leaf and drip of tie centrally in clear cavity and the right way round. - BRE in a paper noted that all steel or iron wall ties installed before 1981 are at risk of premature failure. Due to corrosion. - Chemical i.e. black ash mortar/chlorides - Incorrect spacings or omission of wall ties.

Answer 65

- Omitted where single storey extensions are added and in stepped terrace blocks. - failure to provide a sufficient depth of upstand to the cavity tray; - failure to prevent bridging of the cavity by mortar droppings; - damage to the flexible materials mostly used, nowadays, in the construction of the tray; - failure to support the tray by a mortar bed (haunching); - inadequate lapping or sealing of lengths of cavity tray; and - omission of stop-ends.

Answer 66

Type E cavity trays - preformed of solid DPC polypropylene. Designed for retrofit, brick-sized and can be installed progressively in sections. Only on course disturbed and each unit typically the length of two bricks, causing minimal disturbance. Numerous other types of cavity tray. Type X cavity tray - preformed steppd cavity tray for abutments to gable walls. Type U - undercill envelopment tray. Type K - circular cavity tray for round windows. Type C -preshaped cavity tray for lintel openings.

Answer 67

Oversailing of DPC Buckling or bowing of walls Fracture of the masonry units Fracture of outer cavity wall with no joints

Answer 68

The chipping or breaking off of small pieces of masonry, often due to freeze-thaw cycles or exposure to harsh weather. Other causes include contamination within the masonry and use of a hard mortar with a soft brick eg use of cement based mortar with heritage bricks). Damaged bricks should be replaced.

Answer 69

There are three ratings used to determine the durability of clay bricks as defined by BS EN 771-1. These relate to its ability to withstand frost, based on the level at which frost will damage the brick. ● F0 – No frost resistance: not suitable for external use in construction. ● F1 – Moderate frost resistance: durable unless remaining saturated for long periods or excessive freezing and thawing. They may be suitable for brickwork between DCP and eaves. However, bricks rated at F1 should never be used below DCP, for projecting details or used in landscaping. ● F2 – Frost resistant: suitable for external use with full exposure levels.

Answer 70

Efflorescence is a crystalline deposit of salts that can form when water is present in or on brick, concrete, stone. Most ordinary clay bricks contain sulphates of sodium, magnesium or calcium. These salts are soluble in water, calcium sulphate being less soluble than the other two. Normally, these sulphates are seen as the harmless efflorescence noted, affect appearance only and need simply to be brushed away. Whilst Efflorescence does not cause damage it can be an indication of an underlying defect. Preventing efflorescence ● Ensure new concrete or masonry is cured correctly to minimize moisture retention. ● Applying a water-repellent sealant can help prevent moisture penetration. ● Fix any leaks or drainage issues that are causing excessive moisture. ● Improve ventilation in areas prone to moisture build-up.

Answer 71

BRE 292 - cracking in buildings - discusses sulphate attack of masonry, Sulphate attack relies upon a number of conditions occurring simultaneously; - it requires water saturation over a relatively long period, - a source of sulphates and - a reasonable amount of tricalcium aluminate. Different types of sulphates are more reactive than others, the sulphates of magnesium and potassium are the most aggressive. Ordinary Portland cements vary in the amounts of tricalcium aluminate they contain, those with the highest amounts having the least resistance to attack by the soluble sulphates The reaction is accompanied by a marked volume increase. Wetting of ordinary bricks, therefore, in contact with mortar based on ordinary Portland cement, may lead to the formation of calcium sulphoaluminate and to disruptive expansion. It is, in fact, the mortar which is attacked, not the bricks, and the volume increase consequent upon the formation of calcium sulphoaluminate can cause vertical expansion of brickwork, which is commonly as high as 0.2%. A common consequence of sulphate attack in chimneys and parapets is a pronounced lean caused by the different wetting and drying cycles between different elevations.

Answer 72

- In chimneys and parapets: a pronounced lean caused by the different wetting and drying cycles between different elevations. In chimneys, additional sulphate may be deposited by the combustion process and additional water may be introduced from condensation within the chimney itself. Chimneys tend to lean away from the direction of prevailing weather. - The main sign of trouble on facing brickwork is cracking in the horizontal mortar joints, which generally occurs in a number of them. This may be preceded by some horizontal cracking in the plaster of plastered internal leaves of cavity walls, usually near to eaves level. This internal cracking is caused by the expansion of the outer leaf in which the reaction is taking place, putting the inner leaf into tension. - As the reaction proceeds, the external mortar joint spalls at the surface, and becomes weak and friable. The vertical expansion can result ultimately in spalling of the surface of the facing bricks and some bowing of the external walls. - The brickwork may oversail the DPC at the corners of the building, in a manner similar to that caused by the irreversible moisture expansion. However, the latter movement will take place in the early months of the life of the building, while sulphate expansion is unlikely to appear for several years.

Answer 73

There are three main ways of preventing sulphate attack in mortars: by ensuring that walls do not get, and stay, unduly wetted; by selecting bricks low in soluble sulphates; and by the use of cements low in tricalcium aluminate. Recommended treatment for sulphate damage depends on the severity of the attack, but in all cases, the most important requirement is to remove sources of water. The rebuilding may have to include the use of sulphate-resisting cement, flue linings and, if it is possible from the point of view of appearance, bricks of low sulphate (S2) content. Generally, and in the absence of such obvious causes of dampness, it will be necessary to resort to tile hanging, ship-lap boarding or similar external treatment.

Answer 74

An expansion joint or movement joint is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials. Typically expansion gaps are required in the following materials at the following distances; Clay brickwork 10 - 12 metres Unreinforced concrete panels 6 - 9 metres Lightweight concrete block 6 metres Expansion joints are typically filled with a material capable of being compressed by up to around 50% of its original thickness and which can recover after the thermal movement is reversed. Typical materials include; masonry expansion ties, joint filler (polyurethane) or plastic expansion strip.

Answer 75

Elizabethan / Tudor 1500s - Exposed timber frame infilled with wattle and daub, painted in it’s iconic black and white colours - Only brick was typically used in the chimineys - Glazed windows widely used. Glass is small and imperfect. - 2nd floor typically overhangs the first - Roofs typically relatively steep

Answer 76

- Solid Brick construction. The higher the wall the thicker the base decreasing in thickness in height. - Typically containing brick footings - Use of timber sliding sash windows with window horns - Emerging use of timber suspended floors - Upper floor timbers were built on a corbel or inserted 1brick into the wall - Terrace construction became popular

Answer 77

Concrete foundations required. Cement based mortars rather than lime. Widespread use of brick cavity wall construction. Ground bearing concrete floors. Upper floors were typically hung off joist hangers, steel corbel or 1 brick into the cavity. The introduction of mild and galvanised steel windows that are top or side hung.

Answer 78

Condensation Penetrating dampness Rising dampness Leaks (e.g. from pipework) Trapped construction water (new builds)

Answer 79

Health hazard Reduce strength of building materials Cause movement in building elements Lead to timber decay (dry and wet rot, insect attack) Cause chemical reactions in building components Reduce effectiveness of insulation Damage decorations

Answer 80

Gravimetric testing involves measuring the moisture content using gravity/weight of samples in dry and wet conditions. A sample is weighed, dried in an oven and then weighed again Moisture content = (wet weight - dry weight x 100) / dry weight

Answer 81

Destructive Little practical use on-site

Answer 82

Patination oil is a treatment for lead that prevents the formation of a white, unsightly coating of lead carbonate. Lead carbonate can form when new lead is exposed to moisture, such as rainwater, and can be washed down the roof to stain other surfaces. Patination oil is recommended for use on lead roofing, flashings, and cladding.

Building Pathology Flashcards

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