Building Pathology Flashcards
What his HAC (high alumina cement) and what are the issues with it? How would you identify issues? What remedies are there?
- 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.
What are the typical defects associated with Victorian buildings?
- 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.
What are the typical defects associated with Georgian Buildings?
- 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.
What are the typical defects associated with industrial buildings?
- 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.
What is wet rot? How would you identify it? How would you treat it? What would happen if it was left (prognosis)?
- 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.
What is dry rot? How would you identify it? How would you treat it? What would happen if left (prognosis)?
- 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.
How would you detect woodworm?
- 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).
What is the common furniture beetle?
- 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.
What is the lifecycle of an insect?
- 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.
What are the life stages of a wood rotting fungi?
- 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.
What defects are associated with GRP rooflights?
- 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.
What are the stages of plastisol coating deterioration?
- Loss of colour
- Caulking
- Delamination
How would you test for damp?
- Protimeter
- Dye testing
- Calcium carbide meter
What are the main types of roof covering that could be specified for a flat roof?
- 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.
What is cut edge corrosion? What causes it? How would you remedy it?
- 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.
What is the minimum gradient for a flat roof to shed water effectively?
- Minimum grade of 1:40 is required.
What can cause ponding on a flat roof?
- 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.
What is carbonation? How would you treat it?
- 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.
What is sulphate attack? How can you treat it?
- 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).
Where would you find information on identification and treatment of carbonation in concrete?
- BRE Digest 405
Where would you find information on causes and treatment of rising damp in buildings?
- BRE Digest 245.
Where would you find information for diagnosis and treatment of wet rot?
- BRE Digest 345
Where would you find information on identification and treatment of Dry Rot?
- BRE Digest 299
What conditions does dry rot (serpula lacrymans) require in order to grow?
- Requires hardwood or softwood as food source.
- Requires moisture content of 20% or higher for a sustained period.
- Damp, still air for sustained periods.
What is Japanese Knotweed?
- 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.
How would you positively identify Japanese Knotweed?
- 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.
What are the issues with Japanese knotweed?
- 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.
What are the different growth stages of Japanese Knotweed?
- 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.
What are the remedial options for Japanese Knotweed?
- 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.
What legislation imposes a responsibility on property owners with regards to Japanese Knotweed?
- 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.
What are the pros and cons with the main Japanese Knotweed remedial options?
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.
What advice did you provide your client at Barking with regards to Japanese Knotweed? What remedial option did you choose and why?
- 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.
What is damp?
- 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.
What are the different types of common damp in buildings?
- Condensation.
- Rising damp
- Penetrating damp
What is rising damp? How would you detect it? What are the causes? How would you remedy it?
- 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.
What are tide marks?
- Horizontal lines observed on decorative finishes or building fabrics which show the vertical extent of rising damp. Below which there will be discolouration and general darkness and might be general deterioration to decorative finishes. Hydroscopic salts tend to be concentrated in the tide mark which originate from the ground and are left after evaporation of the ground water.
What is penetrating damp? What are the causes? How would you remedy it?
- Occurs when water penetrates the a building’s envelope.
- Causes can include:
- Saturation of walls exposed to prevailing winds, usually south or south-westerly.
- Defects with masonry walls that allow penetration e.g damaged masonry and lack of pointing.
- Leaking rainwater goods: can saturate the masonry leading to frost damage which then allows water ingress, can also enter into the loft space if sarkiing is too short and guttering overflows due to blockage.
- Defective or missing cavity trays.
- Failed roof coverings (slipped tiles and defective flat roof coverings).
- Remedy includes:
1. Find and rectify the source of the leak.
2. Promote rapid drying (through heating and ventilation or dehumidifier and restricted ventilation).
What is condensation?
- The process whereby water condenses from water vapour to liquid water when the temperature of air containing the water drops to, or below the dew point (temp at which air becomes saturated with water vapour).
- There are two forms of condensation:
1. Interstitial: Occurs within the structure at interfaces between materials and tends to be hidden by construction and surface finishes.
2. Surface: Occurs on surfaces and therefore easier to observe.
What are the causes of surface condensation? What are the signs of surface condensation? How would you treat it?
Surface condensation
- Causes:
1. Cold internal surfaces such as external walls, single glazed windows, cold-water pipes, wall-to-floor junctions, lintels and window reveals.
2. Large amount of excess moisture produced from human activity including cooking in kitchens, bathing, drying clothes inside. This moisture condenses in the rooms where the activities occur but also migrates to where vapour pressure is reduced in areas such as unheated rooms.
3. Excess moisture from unvented or defective flues from paraffin or butane heaters or tumble driers. - Affects:
1. Mould growth - usually more prevalent to areas with restricted air movement such as behind furniture or inside cupboards.
2. Damp patches and spoiling of decorative finishes. - Remedy:
- Mixture of increasing heating and ventilation.
- Modifying human behaviour - heat all rooms of the property and reduce activity that causes excess moisture - shorter showers, dry clothes outside etc.
- Fix any defective flues.
- Increase insulation.
- Install windows with trickle vents.
What are the issues associated with interstitial condensation? How is it remedied?
Issues:
- Can cause dampening of insulation materials which can lead to reduction in performance and eventual physical deterioration.
- If forming against timbers, can promote rot and insect attack.
Rectification:
- Changing of the building detail if there is an inherent defect.
- Replacement of insulation if penetrated such as in a cold roof build up - insulation penetrated by fixings, vapour then passes through vapour control barrier and then into the very cold roof void allowing condensation to form on structural timbers.
Name some typical defects of a Victorian 1800’s (1837 – 1901) ?
- Blocked air vents to ground floors, causing dry rot
- Failed or lack of damp proof course – rising dampness, penetrating damp, efflorescence on plaster, decay to skirtings
- Delamination of brick skins – bulging of brickwork
- Over notching of floor joists for retrofit of services – deflection of floors, reduction in load bearing capacity
- Poorly fitting sash windows, risk of decay within window reveals, water penetration beneath sub-sills, draughty or dangerous operation, decay in concealed areas, lack of security
- Roof covered with concrete interlocking tiles – overloading of roof structure, bowing of rafters and purlins, roof spread
- Settlement of bay windows – internal cosmetic damage, distortion in load-bearing elements
- Wall tie failure (particularly in black ash mortar)
- Heave or subsidence of shallow foundations
- Nail sickness – ferrous nails corroded
Name some typical defects of a Georgian building (1700’s) ?
- Water paths through parapets, hidden valleys and gutters
- Springy floors resulting from decaying timber floor joists. mainly caused by poor cross-ventilation. heel drop test to test the springy floor.
- Rotten or stuck sash windows
- Blocked internal gutters.
- Damp penetration in solid walls
- Corroded cast iron railings bursting stonework
- Bowed brick walls, caused by the practice of lightly bonding high-quality facing bricks in with poorer quality bricks of the main wall, unbonded party walls and front walls and decaying coursed timbers buried in walls
- Failure in roof trusses caused when roof ties rot and begin to spread. Dislodged joists and ridges caused by bomb blast damage.
- Leaning chimneys/over-tall stacks/damp penetration via stacks
- Perforated lead work or splitting caused by over-beating or poor maintenance
- Missing or badly altered load-bearing timber partitions
- Damp basements
- Failure of timber lintels
- Poorly applied or painted stucco limiting water evaporation from walls
- Downpipes decanting on to lower roofs from roofs above, causing temporary flooding in heavy rainfall
What is sulphate attack ?
- Sulphate attack can cause serious damage to brickwork and concrete by creating expansive force that are, or can be, sufficient to disrupt mortar and create significant expansion, bowing and cracking of concrete floor slabs together with related collateral damage.
- In some subsoil there can be a problem with sulphate attack. It occurs when the fill material (hardcore) beneath the slab contains sulphates and these migrate into the concrete. The sulphates react with the concrete causing it to expand.
- Calcium, magnesium and sodium sulphates occur naturally in some clays and other sub soils
- The sulphates dissolve in the groundwater and permeate the concrete.
- This leads to an aggressive chemical reaction between the sulphates in solution and one of the chemicals in the cement.
- The resulting compound expands rapidly as it forms and this can crack the foundation concrete.
- If sulphate attack is a possibility it is wise to use sulphate resisting cement.
What is the life cycle of damp ?
- Spore
- Hyphae
- Mycelium
- Fruiting Body
What is insect attack ?
A generic term that is used to commonly describe the larva stage of wood boring beetles. A number of insects, mainly beetles, are able to use wood as a food source and some of them can cause serious damage to building timbers.
Can you name some types of wood boring insects ?
• COMMON FURNITURE BEETLE (WOODWORM)
3-5m long, dull brown
Lines of pits on wings
Found on or around damaged timber LATE MARCH – EARLY AUGUST (particularly warm weather.
Softwood, European hardwoods
1-2mm dia. Circular flight holes
Flight holes random orientation, mainly in direction of grain.
Bore dust, cream coloured, lemon shaped pellets.
Life cycle 2-5 years
• LONG HORN BEETLE
Adult 10-12mm, black or dull brown.
Sapwood or softwoods particularly roof timbers.
South-west of London mainly surrey.
Flight holes, few large oval, 6-10mm largest dimension.
JULY to OCTOBER
Cream coloured, sausage shaped.
• DEATHWATCH
6-9mm long, chocolate brown
MARCH to JUNE
Bore dust, disc shaped cream pellets
Flight holes circular 3mm diameter
Mostly oak and elm (hardwoods)
• WEEVIL
3-5mm long, brownish black. Distinctive long snout.
All year around.
Flight holes, small ragged, 1mm diameter.
Decayed softwood and hardwoods in damp conditions.
Mostly found in below ground conditions.
Do you have some examples of deleterious materials ?
- Asbestos
- Calcium chlorides
- Calcium silicate bricks
- CFC’s
- Formaldehyde
- HAC (High Alumina Cement)
- Hollow clay pot floors
- Lead
- Nickel sulphides
What is a woodwool slab ?
Used as a permanent shuttering. Formwork is used to contain concrete in order to mould it to the required dims and to support it until it can support itself. It may be left in place for the lifetime of the building.
What are the defects linked to woodwool slabs ?
- Concrete does not adequately get compacted.
- Risk of poor cover to the steel and hence loss of durability, possible reduction in strength, and loss of fire resistance.
- Voiding and honey combing due to vibrations. Poor bond or failed bond between the wood wool and the hardened concrete.
- Buildings constructed from 1950 to the mid-1970s are most likely to be affected by this form of construction.
- If permanent shuttering is discovered, intrusive investigations may be needed to determine the adequacy of concrete cover to the steel reinforcement. If voiding is present, the affected area can be exposed and repaired using hand-fixed concrete repair methods or, if over a larger area, sprayed concrete.
Can you name some concrete defects ?
- Concrete Carbonation
- HAC
- Alkali Silica Reaction
- Chloride Attack
- Sulphate Attack
What is insect attack ?
A generic term that is used to commonly describe the larva stage of wood boring beetles. A number of insects, mainly beetles, are able to use wood as a food source and some of them can cause serious damage to building timbers
What is the life cycle of damp ?
- Spore
- Hyphae
- Mycelium
- Fruiting Body
What are nickel sulphide inclusions ?
Occurs in glass production. Microscopic imperfections in the glass. When the glass is tempered, the nickel sulphide inclusions do not return to the normal low-temp state for several years and expands in the process which can cause cracks with no obvious cause.
Name the three types of asbestos and examples of where they are found.
- Chrysolite – most common asbestos in buildings. Corrugated asbestos cement sheets.
- Amosite – found in fire retardant materials
- Crocidolite – pipe insulation, plastics, cement products.
Ends of the joists in a timber floor built in an external wall have been seriously affected by dry rot. How will you recognise this type of rot and what action would you take to resolve the problem ?
- Features include shrunken wood with cuboidal shapes. Cotton wool type mycelium on the surface. Timber crumbles under finger. Fruiting bodies are red/brown in colour and pancake shaped.
- Identify the rot and where it is at its worst. Remove the cause and strengthen the joists as required or fully replace. If the dry rot has passed through the masonry, this will need sterilisation too.
When was DPC made compulsory ?
1875
Wood wool slabs are deleterious materials. Explain why and where their use would be acceptable.
When used as permanent shuttering for concrete, it may lead to grout loss, honeycombing or voids which can reduce fire resistance, corrosion protection and loss of strength. It is adequate for use in flat roof decking.
Name and describe some deleterious materials.
- Asbestos – Fiberous material used for a variety of reasons from roof sheets to insulation and fire stopping. It is carcinogenic and needs to be removed if there is a risk of release of fibres.
- Lead – Risk of lead poisoning when used for pipes or paint. Contaminates drinking water and risk of inhalation of paint dust or potentially ingested when children chew on painted products.
- Machine Made Mineral Fibres – Potential Carcinogenic. The evidence leads to show there is a high risk and should be treated as such but has not yet been proved.
- Wood Wool Slabs – When used as permanent shuttering for concrete, it may lead to grout loss and inadequate coverage of steels which leads to inadequate fire protection. If used for roof decking, it is not considered deleterious.
- Calcium Silicate Bricks – Shrinks after construction with further movement from wetting. Thermal movement more likely than with clay bricks. Construction details must allow for movement and if designed and used correctly, performs well.
- High Alumina Cement – Gives high early strength and used in maritime buildings. Porosity is increased and resistance to chemical attack is reduced. Where water and chemicals are present in the mix, it can lead to the concrete becoming friable and lead to loss of strength.
What is a deleterious material ?
Any material that is harmful to health, safety, environment, not suitable for their purpose or pose a risk for where it is used.
What are common defects associated with flat roofs and what are the remedies ?
- Crazing - Surface crazing caused by lack of protection from UV exposure. No treatment is required if in small localised patches but should be monitored.
- Ponding - If the gradient is not sufficient and there are dips in the roof finish, it can lead to pools of water. It can lead to water ingress if there is a gap in the roof finish.
- Thermal Movement
- Cracks and splits can occur when there is thermal movement between the substrate and membrane. Usually requires localised repair to the area around the crack.
- Blistering - Caused when water vapour beneath the roof finish increases. The source of moisture should be traced and the blister opened and allowed to dry before patch repairing.
- Flashing and Falls around openings- Defective lead from deterioration or poor workmanship around openings causing water ingress. Depending on the issue with the lead, there are different repairs.
- People - Punctures caused by people from impact damage.
- Cracks and tears along the line of joists - Caused by thermal movement or saturation of insulation or sagging decking. Repaired by cutting felt back and allowing it to dry before patching over.”
Explain why sulphates in hardcore can result in sulphate attack.
As they are not protected with a DPM when they comes into contact with a water source they expand and can transfer this up into the slab above
What is nail fatigue / sickness?
That as a roof ages the fixings which are often iron nails start to fail resulting in tile or slate slippage especially in windy weather conditions.
Replace existing iron nails with copper nails, these do not corrode.
What are the types of wood boring insect that are found near where you work?
- House Longhorn Beetle - only found in Surrey, Berkshire and Hampshire.
How would you treat an insect infestation?
-
What causes spalling masonry?
- Incorrect application of cement pointing: In solid wall buildings, if lime based mortar is replaced with cement mortar the mortar joints cannot release the interstitial moisture within the wall, it therefore is released through the brickwork which leads to spalling due to excess moisture release and makes the bricks more susceptible to freeze thaw as they have a higher moisture content.
- Freeze thaw: Water absorbed through the porous surface of the bricks and then expands upon freezing.
- Crystallisation of salts (cryptoflorescence): this occurs just below the surface of the bricks leading to spalling. Occurs from large build up of salts and usually occurs where older, weaker bricks are re-used inappropriately in areas of excess dampness (at ground level which is susceptible to splashback - should use engineering bricks).
How would you test for damp? What are the pros and cons of each of these methods?
Carbide meter:
- Sample of mortar, plaster or brick taken and weighed.
- Sample then placed in one chamber, a weighed amount of calcium carbide powder is placed in a separate chamber.
- Container then shaken to allow mixing of two materials. The amount of acetylene gas produced indicates the amount of moisture present.
- Pros: accurate.
- Disadvantages: intrusive, more time consuming that protimeter.
Moisture meter:
- Measures level of conductivity, water has high conductivity so increases the reading when present.
- Pros: Quick, non-intrusive (relatively).
- Disadvantages: Calibrated for timber, can give false high readings from highly conductive materials such as salts, foil backed plasterboard and black ash mortar.
Deep wall probe:
- Essentially a long protimeter than can measure conductivity deeper within the wall.
What are the three types of loading on buildings?
- Dead load: load imposed by the structure itself.
- Live load: load imposed by occupants and objects in a structure.
- Environmental load: load imposed by rainfall, snow and wind.
What kind of issues would you expect to find with underground drainage from CCTV surveys?
-
Why did you recommend wholesale replacement of the roof covering at St. Leonards?
- I actually recommended that some opening up works were conducted internally to determine the extent of the water ingress and extent of damage to the structural timber and roof deck.
- After inspection it was apparent the entire roof deck was saturated and rotten in widespread areas and would require wholesale replacement.
- As the existing reinforced bitumen felt roof covering showed widespread developed crazing and isolated blistering it was clear that it was at the end of its life and would therefore require replacement too.
- I consulted the BRE Good Repair Guide - Flat Roofs: making repairs to bitumen felt and mastic asphalt roofs.
What other types of invasive species are you aware of?
- Giant Hogweed.
- Horse tail.
- see conors slides.
What information could you consult with regards to dealing with Japanese Knotweed?
- Property Care Association Code of Practice.
What are the main ways you can eradicate JK?
Dig and dump (excavation of the plant and roots)
- JK infested soil excavated (up to 3m vertically and 7m horizontally from the area of growth), removed off site and disposed in an appropriately licenced waste management facility as it is classed as controlled waste under the Environmental Protection Act 1990.
- Benefits: quick, no restrictions on site for development, works can continue on site immediately.
- Drawbacks: Expensive (£70 per tonne), reduced valuable landfill capacity (should be last resort), increases risk of spread (disturbing the plant through excavation)
On-site burial
- Trench is excavated on the site in suitable location and JK then excavated and buried in the trench which will need to have at least 5m of overburden. Unless JK can be buried with 5m of overburden then a specialist root barrier membrane must be used to partly or full encapsulate the JK. Area is then monitored for at least two successive growth seasons and treated with herbicides if needed.
- Benefits: More cost effective than dig and dump, works can continue immediately, quick to remove.
- Drawbacks: Need suitable set aside area where the JK will not be disturbed, can’t be used if water table is high (allows distribution of JK into waterways), if root barrier used it needs to be installed correctly as any weaknesses / tears can be exploited by JK, JK can be accidently spread during excavation.
Herbicidal treatment
- Herbicides applied to JK usually combined application of spraying and stem injection.
- Benefits: Cost effective, can be carried out in situ (less risk of spread), quickly reduces spread and ability to impact structures, can be used on restricted sites that don’t have a set aside area.
- Drawbacks: JK remains in situ do could be disturbed and spread (particularly if works being carried out), not appropriate for sites where there is planned development (excavation), take several years to achieve complete eradication with two years of monitoring to ensure growth has ceased.
Other options:
- Biological control - testing being undertaken - still not used.
- Screening / sifting - JK excavated along with soil which is then sifted to separate rhizomes which are disposed of appropriately, the soil is then screened and stored on site in a suitable location, treated with herbicide and monitored.
What the positives and negatives of cold and warm flat roofs?
Cold roofs:
- As the roof void is cold there can be issued with interstitial condensation as warm air from inside the building enters the unheated roof space allowing condensation to form on the timber roof joists and deck - this make them susceptible to rot and therefore structural failure eventually. Require vented 50mm gap between bottom of roof deck and top of insulation to try and prevent.
- More complicated to construct - insulation between the joists rather than just on top of roof.
- Greater chance of thermal bridging - ceiling joists are not insulated.
- Benefit: as insulation is between joists there is no change to roof height - this could affect roof height relative to the parapet walls - may need to extent them etc
Warm roofs:
- Easier to install.
- Can be retrofitted.
- Less chance of thermal bridging.
- Drawback - external roof height will be raised.
How did you know that you were dealing with penetrating damp with the property at Hastings and not condensation or rising damp?
- It was clear to see that the roof covering had failed in numerous areas and water could be seen dripping through the underside of the roof deck. There was also staining and areas of plasterboard soffit that were saturated and had fallen in isolated areas.
- Rising damp would have been localised to the walls and tide marks would have likely been present to a height of circa 1.3m with spoilt decorative finishes, staining and blown plaster below.
- Condensation was present to the internal windows but I believe this was a result of the building being unheated, unventilated and having excess water vapour from the penetrating damp.
What did you do / what did you advise for the JK removal at Barking?
- I advised my client that if the JK was not treated it could continue to spread and damage the adjacent hardstanding and security hut by exploiting structural weaknesses and causing cracking in addition to causing cracking of mains water and drainage pipework which I know were in close proximity to the infested area.
- I also advised that the client that under the Wildlife and Countryside Act 1981 they were obligated to control its spread and prevent spread onto neighbouring properties.
- I then considered the potential remedial options but recommended that herbicidal treatment should be utilised on the basis that the site had a high water table and no suitable area to dispose of the JK to allow on site burial and also that excavation should be used as a last resort, would be considerably more expensive and may lead to further spread of the JK.
- I advised that the client that as JK had been identified, the client should instruct a JK contractor to map the entire site to confirm the extent of the growth and make sure there were no other areas of infestation.
- I also advised that the client should ensure that they had a 10-year guarantee with the treatment to give comfort to the incoming tenant on a 10 year FRI-lease.
If you identify movement in a building, what further investigations might you wish to undertake?
- Environmental matters, i.e. trees in close proximity
- Neighbouring dwellings
- Engineers structural survey
- CCTV Drainage survey
How did you know that you were dealing with penetrating damp to the internal elevation of the property in Hastings (not the roof)?
- The staining and deterioration to the internal plasterboard / decorative finishes was patchy and concentrated in numerous areas along the length of the elevation. If it was rising damp I would expect to see a linear tide line around 1.3 m max height.
- I was lucky that the second time that I visited the property there had been a sustained period of rainfall and I could see that the areas of staining observed previously had darken.
Can you confirm another scenario where you may have penetrating damp through a wall?
- Solid walls: leaking mortar joints (need to be raked out to a depth equivalent to their height and then repointed), masonry water repellent to less exposed elevations, defective jointing details around windows etc.
- Cavity walls: Rarer but could have bridging of cavity by wall cavity ties sloping inwards (will see regular spots of ingress), bridging of the cavity wall by it being blocked above the DPC from mortar droppings and other debris, missing cavity trays.
What concrete defects are you aware of?
- Carbonation
- HAC
- Sulphate attack
- Regent’s Street disease
You say you are aware of common building defects, give some examples of defects you would find in residential, industrial and office buildings.
Residential
Georgian
- Water ingress through parapet walls and valley gutter details.
- Missing or poorly altered load-bearing timber partitions.
- Failure of roof trusses
- Poorly applied or painted stucco limiting water evaporation from walls
- Rotten or stuck sash windows
Victorian
- Defective slates and nail sickness.
- Deflection of roof timbers caused by installation of heavier concrete tiles (cheap).
- Blocked air vents to suspended timber floors from removal or raising of external pavement level.
- Lack of lateral support between terrace houses (known as the book end effect); joists run parallel with part walls.
Modular - Post Second World War
- Use of asbestos sheets to roofs.
- Corrosion of steel frames used.
- Alkali Silica Reaction affecting concrete frames (gel
General housing (modern)
- Cracking and movement of walls due to timber frame being wet and then shrinking once dried out.
- Heave / subsidence.
Industrial
- Impact damaged cladding.
- Cut edge corrosion.
- UV degraded roof lights.
- Asbestos roof sheets.
Office Buildings (60s-80s)
- Hollow clay pot floors - can exhibit loss or strength due to honeycombing of the structural concrete ribs of the floor system which reduces structural integrity and fire stopping capabilities. Incorrect removal of topping screed if structural to gain floor height can lead to structural failure.
- Wood wool cement board - WWCB is formed of softwood shavings which are coated and bounded by Portland cement. WWCB was commonly used as permanent shuttering in flat slab or ribbed reinforced concrete floors. There is risk of poor concrete cover to the steel structural members therefore reduces durability, structural integrity and fire resistance. If discovered the shuttering be removed to determine coverage and parch repairs undertaken by hand if necessary.
What is Regents Street Disease? What are the methods of rectification?
- Found in early 20th century load bearing steel framed buildings clad externally with stone, brick and terracotta that is notched around the steel frame and then the void filled with low grade mortar. Corrosion of the steel frame due to oxygen and moisture causes corrosion and expansion and with no void space causes cracking of the mortar and overlying cladding.
- Can usually diagnose from cracks delineating the frame.
- 2 main ways to rectify:
- Exposing the steel, cleaning it and protecting it and then create a void around steel frame to allow movement.
- Use cathodic protection: system relies on concealment of discrete anodes into the stone joints and electrical connection to the steel frame and the introduction of an electric current to reverse the corrosion process. Requires detailed design to ensure harmful currents arnt produced and maintenance.
What are the common concrete defects you know? What causes them? How are they rectified?
What is heave, subsidence and settlement? What causes them?
Heave:
- The upward movement of the ground beneath a building as a result of the soil expanding.
- Causes: Tree removal (increase in soil moisture), frost heave, burst sub terrain water pipes.
Subsidence:
- The ground beneath a building sinks, pulling the property’s foundations down with it.
- Causes: Prolonged dry spells particularly with clay rich soils, trees drawing moisture and collapsed mines.
Settlement
- Downward movement due to compression of soil due to weight of building within 10 years from construction.
- Causes: occurs after construction.
What typical defects would you expect to find in a 1960s high rise office building?
- Asbestos.
- Concrete carbonation of the concrete frame.
- HAC.
What is radon? Which areas would you find it? How do you deal with it?
- Radon is a natural, colourless, odourless, radioactive gas formed by the radioactive decay of uranium that occurs naturally in rock and soil.
- Exposure to particularly high levels of it may increase risk of developing lung cancer.
- Some areas of the UK have higher concentrations due to geology and soils e.g Cornwall, Devon and Sommerset.
- Radon can build up in some underfloor areas and enter a building. Youhttps://www.brainscape.com/l/dashboard/building-surveying-apc-19728728/decks/11173470/cards/376263225/edit can take some of the following steps:
- A well installed damp proof membrane (radon barrier).
- Air vents (with fans if needed).
- Radon sumps.
- There are others.
What are the options for damproofing a basement?
Type A: Basement tanking used internally or externally (applied during the construction process). Any defects to the membrane will have damaging consequences and those defects to external tanking systems will be impossible to rectify. Internal tanking systems can be penetrated by fixings and can be displaced by build up of hydrostatic pressure.
Type B: Structurally integrated protection whereby waterproofing is provided by walls themselves (reinforced / prestressed concrete). Need to carefully consider jointing details as they can leak.
Type C: Drained cavity system whereby water is allowed to pass through the external skin into the cavity and is then pumped away by an electric pump. Can be problematic when there is a high water table and failure of pumping system (usually due to accumulation of fine silts etc).
How do you interpret cracks?
Subsidence cracking: Usually diagonal, runs through masonry and blockwork and usually wider at top than bottom.
Heave cracking: Usually wider at base and as above.
Appoint a structural engineer!
How do trees negatively affect buildings?
- Can pull more moisture of soil, particularly during dry seasons causing subsidence and then once removed can lead to excess moisture and heave of soils.
- Roots dont usually directly affect buildings, they damaged water and drainage which then cause issues.
- Oak and Poplar have strong root activity.
- Safe building distances vary but good rule of thumb is to limit proximity of tree equivalent of that of its full maturity height.
How would you rectify subsidence of foundations?
