Building Pathology Flashcards
1
Q
What his HAC (high alumina cement) and what are the issues with it? How would you identify issues? What remedies are there?
A
- HAC contains calcium aluminates which is found in certain types of clay.
- HAC initially used for maritime application - develops strength rapidly.
- HAC was used for structural concrete during the 70s in particular.
- Undergoes mineralogical change called conversion - increases its’ porosity and susceptibility to chemical attack.
- ## Conversion is identified by concrete becoming friable and changes to a chocolate brown colour.
There are three main stages in relation to investigating HAC which include:
- Identification - assessing the areas affected.
- Strength assessment - confirm the structural strength of the affected elements e.g precast concrete beam.
- Durability assessment - confirms the long term durability of the concrete and risk of chemical attach to associated reinforcement - involves petrographic analysis.
2
Q
What are the typical defects associated with Victorian buildings?
A
- Differential settlement of part basements in terraces.
- Lack of lateral support between terrace houses (known as the book end effect); joists run parallel with part walls.
- Blocked air vents to suspended timber floors from removal or raising of external pavement level.
- Defective slates and nail sickness.
- Sagging roof timbers; can be from replacement of slates with cheap + heavier cement roof tiles.
- Lead water pipes.
- Rot and creep in timber members.
3
Q
What are the typical defects associated with Georgian Buildings?
A
- Water ingress through parapet walls, valley gutters.
- Decayed timber to floor joists: can be poor cross ventilation to floor voids in long narrow terraces.
- Failure of roof trusses when roof ties rot due to past unknown bomb damage.
- Missing or poorly altered load-bearing timber partitions.
- Damp basements.
- Poorly applied / painted stucco plaster preventing moisture escape.
4
Q
What are the typical defects associated with industrial buildings?
A
- Cut edge corrosion.
- Delaminating plastisol finishes.
- Missing caps to fixings.
- Leaking gutter joints.
- UV damaged roof lights.
- Cracking – subsidence, heave, settlement etc.
- Impact damaged cladding.
- Asbestos.
- Carbonation.
- Cracked floor slabs.
5
Q
What is wet rot? How would you identify it? How would you treat it? What would happen if it was left (prognosis)?
A
- Most common type is Ciniophora Puteana (known as cellar fungus).
- Highly vulnerable to fluctuations in moisture and thrives in timber with 50-60% moisture content.
- Identified by
- Surface cracks that follow the line of the timber grain.
- Thread-like strands of hyphae which are yellowish and become darker brown with age.
- Fruiting body rarely found.
- If fruiting body is present (usually outdoors) it is this olive brown plate irregular in shape with a knobbly texture.
- Treatment:
1. Locate and eliminate source of moisture.
2. Promote rapid drying.
3. Determine extent of damage.
4. Remove timber 500mm beyond affected areas.
5. Treat infected timbers and install new pre-treated timber. - Not as severe structurally as dry rot but can eventually cause failure.
6
Q
What is dry rot? How would you identify it? How would you treat it? What would happen if left (prognosis)?
A
- Timber decaying fungus (Serpula Lacrymans) that digests softwood and hardwood timber, reducing its structural integrity.
- Is not found in nature – only in internal timber constructions.
- Identifiable by:
1. Timber can crumble.
2. Mushroom odour.
3. Dull brown colour.
4. Defined cuboidal cracking.
5. White, fluffy mycelium or can be pearly grey and white sheets (depends on humidity).
6. Pancake shaped / bracket shaped fruiting bodies with white edges and rusty red colouration (spores). - Treated by:
1. Locate and eliminate source of moisture - survey structure and identify issues (defective plumbing, rainwater goods, damaged rendering, defective roof coverings etc).
2. Promote rapid drying - Heat the building and allow sufficient ventilation. Can use dehumidifiers but ventilation will need to be reduced to work. Remove floorboards adjacent to wet walls if necessary and increase / ensure sub floor ventilation - can even install heavy gauged polythene sheeting to oversite where floor is particularly wide.
3. Determine full extent of the outbreak - survey visually but also use screwdriver to detect softened wood. Where timber floor joists are suspected to be infected and embedded in walls plaster will need to be removed. Skirting boards and floor boards may also need to be removed.
4. Consult a structural engineer if structural timbers are suspected to be compromised.
5. Remove rotten wood - cut away 450mm beyond furthest extent of infected timber. Treat walls with fungicidal fluid. Apply sound timbers with preservative via repeat application to drilled holes, application of proprietary pasts of insertion of borate rods to ensure deep penetration. Then install new pre-treated timber.
6. Monitor.
Prognosis:
- Left untreated it will spread to other timbers through masonry and plaster and caused structural failure.
7
Q
How would you detect woodworm?
A
- Bore dust (can collect in cobwebs under affected timber) and flight holes (1-2mm in diameter with more recent holes having
sharp edges and lighter inner sides due to oxidisation not yet dulling the exposed timber).
8
Q
What is the common furniture beetle?
A
- Type of woodworm responsible the most timber damage in the UK.
- Emergence between May – September.
- Found in softwoods, EU hardwood and plywood.
- Found in timber with greater than 12% moisture content.
9
Q
What is the lifecycle of an insect?
A
- Eggs laid by female in cracks / splits of timber or old flight holes
- Larvae hatch and then burrow into wood eating sap (when most damage done which isn’t visible)
- Adult insect emerges from pupa skin and bores way out of timber forming exit holes.
- This process can take a number of years to occur.
10
Q
What are the life stages of a wood rotting fungi?
A
- If conditions are favourable spores will germinate.
- Spores then develop root like filaments called Hyphae which penetrate timber.
- Mass of Hyphae form, called mycelium which is then visible to the naked eye.
- If conditions are favourable then a fruiting body may form.
11
Q
What defects are associated with GRP rooflights?
A
- Loss of transparency, embrittlement etc caused by ultraviolet light breaking down polymers in the rooflight plastic.
- Incorrect installation: 2 lines of sealant should be installed to each end of a rooflight (usually recommended by manufacturer’s).
- Embrittlement of foam fillers by UV degradation.
12
Q
What are the stages of plastisol coating deterioration?
A
- Loss of colour
- Caulking
- Delamination
13
Q
How would you test for damp?
A
- Protimeter
- Dye testing
- Calcium carbide meter
14
Q
What are the main types of roof covering that could be specified for a flat roof?
A
- Reinforced bitumen membranes: Constructed by bonding 2 or more layers of reinforced bitumen with hot bitumen (can also get
single layer RBM systems too). - Polymetric singl-ply: PVC. Laid and can be fully fastened, fully adhered, or loose laid and ballasted.
- Mastic asphalt: Graded limestone aggregate bound together with an asphaltic cement (bitumen). Heated to 210 degrees and
applied with a wooden float. - Liquid roof systems: Monolithic, fully bonded, liquid-based coating with a rubberised finish.
- Profiled sheets.
- Lead, zinc, copper and steel sheet.
15
Q
What is cut edge corrosion? What causes it? How would you remedy it?
A
- Caused by cutting each profiled metal roof sheet to length, causes micro cracking of the protective corrosion which lead to
corrosion of underlying metal in presence of moisture. - Can be caused by moisture being trapped in lap joints (held by capillary pressure) – breaks down protective coating.
- Dirt traps can occur at edge of sheet (if levels off) which can lead to further dirt and moisture build up = deterioration of
protective coating + corrosion. - Issue treated by cleaning the affected area (chemical cleaner/blast cleaning etc) then applying silicone based paint system
over priming layer according to manufacturer’s instructions. E.g Girosil Edge RC-E.
16
Q
What is the minimum gradient for a flat roof to shed water effectively?
A
- Minimum grade of 1:40 is required.
17
Q
What can cause ponding on a flat roof?
A
- Tapered insulation or roof deck not laid to correct falls (timber firrings used to set roof deck falls).
- Deflection of timber roof deck - through reduction in structural integrity of structural timbers - rot / insect infestation.
- Blocked rainwater goods.
- Subsidence / heave.
18
Q
What is carbonation? How would you treat it?
A
- Carbonation occurs when the alkaline elements of the concrete react with the
atmospheric carbon dioxide creating calcium carbonate which lowers the PH level of the
concrete and therefore reduces the passivity of the concrete. It will cause gradual
neutralisation of the alkalinity from the surface inwards. Should there not be adequate
coverage of steel reinforcement within the concrete, carbon dioxide can react with the re-bar
and cause corrosion and spalling of the overlying concrete – then allows further moisture ingress and corrosion. - Should have 50mm concrete cover, can be as little as 10mm in older high rise flats!
- Test: drill 10mm diameter holes into concrete and break out section of concrete between. Treat freshly exposed concrete with phenolphthalein (concrete will turn pink if un-carbonated).
- Rectify: Hack off loose / defective concrete, grit blast all corrosion to steel, apply proprietary bar primer and patch repair area with mortar repair system e.g SIKA Ferrogard.
19
Q
What is sulphate attack? How can you treat it?
A
- A chemical reaction affecting concrete causing it to expand and crack. Externally this is due to the penetration of sulphates in solution (usually carried in groundwater) coming into contact with the concrete. Internally, this can be due to introduction of sulphates into concrete during the mixing process e.g sulphates in the hardcore beneath a concrete floor slab.
- Can affect foundations and concrete floor slabs (concrete floor slabs are now required to be separated from the ground by polythene sheeting under building regs).
- For foundations that may be susceptible you can spec Type 2 Portland cement (moderate resistance to sulphates) or Type 4 /5 cement (for very high resistance).
20
Q
Where would you find information on identification and treatment of carbonation in concrete?
A
- BRE Digest 405
21
Q
Where would you find information on causes and treatment of rising damp in buildings?
A
- BRE Digest 245.
22
Q
Where would you find information for diagnosis and treatment of wet rot?
A
- BRE Digest 345
23
Q
Where would you find information on identification and treatment of Dry Rot?
A
- BRE Digest 299
24
Q
What conditions does dry rot (serpula lacrymans) require in order to grow?
A
- Requires hardwood or softwood as food source.
- Requires moisture content of 20% or higher for a sustained period.
- Damp, still air for sustained periods.
25
Q
What is Japanese Knotweed?
A
- A herbaceous perennial plant that is a non-native, invasive species in the UK.
- First introduced for ornamental purposes in the mid 1825 century but now very invasive due to lack of enemies such as insects, bacteria and fungi that are only present in it’s country of origin.
- JK grows through spreading of rhizomes laterally.
- Causes circa. £165m per year.
- Commonly found around public waterways and railway tracks.
26
Q
How would you positively identify Japanese Knotweed?
A
- Green, shield shaped leaves with flattened bases.
- Hollow, bamboo-like stem which is light green with speckled red colouration.
- Small, clustered creamy-white flowers.
- Thick and extensive rhizomes which are orangey-yellow internally.
27
Q
What are the issues with Japanese knotweed?
A
- Rhizomes can exploit cracks and structural weaknesses in building fabric or existing cracks causing progressive cracking and loss of structural integrity. This can occur in foundations, walls, retaining walls, hardstandings (through movement joints and weaknesses in incorrectly laid hardstandings).
- Rhizomes can also physically move and block underground services such as drainage and water pipework in addition to affecting buried cables.
- Can prevent homebuyers from gaining a mortgage from a preferred lender and some do not cover JK.
- Can cause diminution in land / property value.
- Can spread very easily to neighbouring property - 0.02g of rhizome needed to allow regrowth.
28
Q
What are the different growth stages of Japanese Knotweed?
A
- Spring: emerging stems that can range from green to red and purple with rolled leaves.
- Late summer / early Autumn: Creamy-white flowers form in drooping clusters.
- Autumn / winter: Stems only present and turn various shades of brown, sometimes with orange tinge.
29
Q
What are the remedial options for Japanese Knotweed?
A
- Excavation and disposal: Excavation can extend up to 3m vertically and 7m horizontally from the above ground growth. Is then taken to appropriately licenced waste management facility.
- Onsite burial and encapsulation with membranes: Excavated then buried on site, if can’t be covered with 5m of overburden a specialist root membrane must be installed or the Japanese knotweed will be completely encased with root barrier if it cannot be completely buried.
- Chemical control with use of specialist herbicides applied by mixture of stem injection and localised spraying.
- Biological control: introduction of a ‘pest’ species that will attack the JK. Trials currently being undertaken with Japanese sap sucking insects. However will not control infestation on its own.
30
Q
What legislation imposes a responsibility on property owners with regards to Japanese Knotweed?
A
- Wildlife and Countryside Act 1981 - it is an offence to plant of otherwise cause Japanese Knotweed to grow in the wild.
- The Duty of Care Regulations 1991 - Japanese Knotweed is classed as controlled waste and therefore owners owe a duty of care when handling and disposing of it.
31
Q
What are the pros and cons with the main Japanese Knotweed remedial options?
A
Herbicidal treatment:
+ Cost effective.
+ Carried out in situ - less risk of accidental spread.
+ Quickly reduces ability of JK to spread and impact structures.
- Can take years to complete treatment (3 year course then monitoring).
- Not appropriate where development is planned - will cause spreading.
- Continued monitoring required 2 years post treatment to confirm rectification.
Burial:
+ Work can continue immediately after burial.
+ Quick.
- May not be possible to burry on site - buried services etc.
- Not possible if water table is high.
- Rhizomes can be accidently spread.
Excavation and offsite disposal:
+ Quickly removes JK.
+ No restrictions left on site.
+ Works can continue immediately.
- Expensive.
- Reduces valuable landfill capacity.
- Increased risk of spread.
- Should be used as a last resort measure.
32
Q
What advice did you provide your client at Barking with regards to Japanese Knotweed? What remedial option did you choose and why?
A
- Explained that the client had a statutory obligation to prevent its’ further spread under the Wildlife and Countryside Act 1981.
- Stated the implications if left to spread - could spread to where site incoming water and outgoing drainage were and near security hut.
- Recommended that although I had identified it, a Japanese Knotweed specialist surveyor should be instructed to map the area and provide recommended remedial options and reasoned professional advise.
Herbicidal treatment was chosen on the basis that:
- Water table was particularly high on site - couldnt burry.
- Chemical treatment would take longer but reduced chance of disturbance and spread of JK.
- Land was an existing site and not going to be developed in the foreseeable.
- 10 year guarantee was issued - this was a condition of the new incoming tenant looking to let the property on a 10 year FRI lease.
33
Q
What is damp?
A
- Whereby the level if moisture inside a building reaches a level that causes building defects such as staining of decorative finishes, mould growth, frost damage and sulphate attack.
34
Q
What are the different types of common damp in buildings?
A
- Condensation.
- Rising damp
- Penetrating damp
35
Q
What is rising damp? How would you detect it? What are the causes? How would you remedy it?
A
- It is the result of water being drawn up through porous masonry from wet ground via capillary action.
- It can be detected by horizontal tide marks up to 1.3m in height (any further vertical movement is prevented by gravity), blown plaster and spoilt decorative finishes.
- Causes include:
1. No DPC.
2. DPC bridged (render, soil, raised external paving, covering, removed or blocked vents to suspended floors, poor underfloor ventilation). - Remedies include:
1. Installation of DPC.
2. Electro-osmotic damp proof course.
3. Chemical injected DPC.
4. Increase internal ventilation and heating.
