Building Pathology Flashcards
What is 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? (1840-1900)
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.
Walls - No DPC (1875 Public health act)
Snapped headers. Poor restraint (wall ties)
Removal of structural partitions
Timber lintels and decay
Floors - Over notching of joists
Blocked air bricks/poor ventilation
Timber decay
Built in timbers prone to decay
Deleterious Materials -
Lead paint
asbestos
anthrax
What typical building defects might you expect to see on a Victorian residential property?
no, or incorrectly installed DPC. (used slate or engineering bricks from 1875 which can crack with movement)
Incorrect repointing with cement mortar
Inadequate foundations in cheaper properties
undersized floor joists that can’t accommodate modern furniture
Penetrating damp damaging ends of timber joists and lintels.
Inadequate ventilation of subfloor
slate delamination and nail sickness
Insect attack
What are the typical defects associated with Georgian Buildings? (1775-1849)
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.
Walls - No DPC
-Snapped headers, poor restraint (wall ties) bulging walls.
- Stone defects and sulphur attack
- Damp penetration through thin walls
- Timber lintels and decay
- Cracking stucco render/water ingress.
Foundations - shallow
Finishes - Lime plasters replaced with modern gypsum or cement
Deleterious materials - lead paint
- Asbestos
- Anthrax
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.
Typical defects found in properties from 1930-1940?
Walls
Cavity wall tie failure
Steel frame corrosion
Cementous Renders (not breathable)
Introduction of prefabrication (concrete defects)
Windows
- Metal crittal windows (Corrosion)
Deleterious materials
Asbestos
Mundic
Typical defects found in properties aged 1960-1970?
Roofs -
Wood wool & strammit board roof deck
HAC
Asbestos
Cut Edge Corrosion
Walls -
Concrete chemical attack (carbonation)
Boot lintels
brick slips concrete frames, thermal movement - fall off
Calcium Silicate Brickwork
Mosaic tiles - loss of adhesion
Calcium Chloride Additive - increases corrosion
GRC Cladding - loss of strength
Floors
Wood wool slabs
lack of movement joints
made up ground
removal of soils due to failed internal RWGs subsidence
Deleterious Materials
Asbestos
HAC (High Alumina cement)
Calcium Chloride
Nickle Sulphate Reaction
Name some defects found in modern properties (1980 - present)?
Roofs
Cut edge corrosion
Flat roof issues
Poor insulation
Curtain walling detachment
Symphonic drainage systems
Walls
- Rotation of short returns
lack of expansion joints
- Composite panels fire risk
nickel sulphide inclusion in glass
Deleterious materials
Asbestos (up to 1999)
Wood wool slabs
Defects found in pre 1990 properties?
Bridge failed or lack of DPC
Poor ventialtion to floor voids
Poorly fitted sash windows
Leaking services/rainwater goods
Modern concrete tiles (overloading)
Lack of restraint to the walls
Concrete/hard mortar/pointing
Lead paint
Removal of load beating internal partitions
Differential settlement to bay windows
Insect attack
What is mundic block
Blocks produced from waste rock worked from mining, quarrying and beach gravel. The blocks breakdown overtime. The blocks typically degrade from the inside of the cavity to the surface.
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 are the classifications of mundic block
A1 - Sound concrete in satisfactory condition
A2 - Concrete suitible subject to protection and maintenance
A3 - Stage 3 tested containing less than 30% possible problem aggregates
B - Contains more than 30% possible problem aggregates although appears sound
C - Clearly unsound from examination
Options A1-3 are morgagable, B-C are not.
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).
Identification of sulphate attack?
Located in brickwork, blockwork, render and concrete.
Heave in concrete slabs and displacement of adjacent masonry
In dwellings with timber floors, the sleeper walls may become displaced causing deflection in floors
Cracking
Spalling
Loss of strength
Increase surface area for further attack
Friable
Edges and corners susceptible
Upwards bowing coupled with map pattern cracking and possibly displacement of brickwork at slab level are common indicators. Visual indicators of affected concrete may be the existence of flaky or crumbly concrete
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 legal restrictions are there in dealing with knotweed?
Offence to plant or grow it. Illegal to cause spread. Classed as controlled waste and requires a licence to dispose at licensed sites.
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.
How do you test for damp?
The use of a protimeter / moisture meter or a Speedy Carbide Meter can be used to establish the moisture content of walls, and the level of damp occurring.
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.
What are Vapour barriers and why do we use them?
They are put in roofs and some cavity walls to prevent moist air penetrating to a point where it might need its dew point temperature and cause interstitial condensation.
What ways could moisture enter the building? How would you differentiate between the different types?
Penetrating damp — moisture gets into the building because there is a porous bridge transferring moisture by capillary action from the external face of the walls to the internal face of the walls. Could be a single skin of masonry, water trapped behind render, mortar snots on cavity ties etc. Or there is a hole in the roof which allows moisture in through and it gets to the ceiling due to the force of gravity. I would identify it based on its location further investigation
of the cause of the moisture.
Rising damp — Moisture rising up the wall from the ground due to capillary action normally up to a
maximum of lm high tide marks. Identify through a visual inspection of its location and extent and
also use moisture meter to confirm that the moisture content starts off high and gets lower before cutting off at approx 1 m. Identify if there is a DPC is something bridging that DPC. Ensure there are no other possible causes.
Condensation — Hot moist air hits a cold surface and condenses causing the surface to absorb
the moisture which encourages staining and mildew growth. Identify it through the distinctive
mildew, the location poorly ventilated areas with high humidity, kitchens, bathrooms, bedrooms, rooms used for drying clothes.
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
What are the typical spacings for wall ties?
900mm centres horizontally
450mm centres vertically
300mm away from windows
What buildings are most likely to be at risk from cavity wall tie failure?
cavitys built before 1981 due to the life expectancy of galvanising. Until 1970 twisted butterfly ties were also still in use.
How would you replace defective wall ties?
Use a metal detector or boroscope to determine location.
remove defective and replace with new by drilling into the wall
What is Efflorescence?
Visible on brickwork and caused by soluble salts being brought to the surface as the wall dries out.
Shown as White Staining
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
Discuss the likely causes of a leaning chimney breasts and the remedial work.
A combination of erosion, acid attack and salt crystallisation are liable to cause a chimney to lean (see illustration). The BRE Good Repair Guide says any chimney that leans more than 1nnnn in 100mm is unsafe
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
Name some hazardous materials?
Asbestos
CFC’s (Chlorofluorocarbons) (think air conditioning refrigerants)
HCFC’s (R22. Banned from January 2015)
Crystalline Silica (Found in building materials. Dust can result in silicosis (lung
disease)).
Formaldehyde (Carcinogenic material used in foam and timber-based
building materials)
Lead (used in roofing, waterpipes and paint) (Carcinogenic and teratogenic)
Machine Made Mineral Fibres (MMMF) (Respiratory issues)
Continuous filament (glass wool)
Insulation (rock wool or slag wool)
Ceramic Fibre
Special purpose fibre
- Coal Tar
- Anphrax Horse Hair
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 - co2 in air
HAC
Alkali Silica Reaction
Chloride Attack - chloride attacks steel
Sulphate Attack - sulphates in soil
What are the symptoms, methods of testing and treatment of Concrete Defects?
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 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 (insulating board)
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.”
What is Thermal movement
Thermal movement refers to the expansion and contraction of building materials in response to temperature changes. When materials heat up, they expand; when they cool down, they contract. This movement can cause various issues in buildings, such as cracking, warping, or structural stress
What is the minimum fall for a flat roof?
1:40. Best practice more like 1:60
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.
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 other types of invasive species are you aware of?
Giant Hogweed.
Horse tail.
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
Better thermal performance
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?
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 a property (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.
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 is the difference between settlement and subsidence?
Settlement is caused by the building drying out following construction - usually seen internally
Subsidence is caused by downward movement of the ground, so for example by damaged drains
subsidence cracks are generally more than 3mm and visible on the outside and inside of your home. Diagonal and usually wider at the top.
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.
Where a property is suffering from subsidence, what type of cracking might you expect to see?
diagonal cracking along brickwork
cracking wider at the top
close to weak points in the structure such as windows and doors
visible internally and externally
What type of soil is susceptible to heave and what are the possible causes?
Cohesive soils such as clay. Possible causes include removal of trees, change in water table,
leaking drains or inadequate foundations that are built within the movement zones.
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.
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).
Types of brick cracking
Subsidence — A movement down in the ground level. In clay soil, the growth of large trees which
remove water from the ground can cause this. This leads can lead to vertical cracking if in the centre
of the building or diagonal cracking if at the corner of the property. The cracks will be larger at the
top and thinner at the bottom.
Heave — A movement upwards in the ground level. In clay soil the removal of a tree will lead to an
increase in the moisture content of the soil which will cause the soil to swell. This leads to vertical
cracking if in the centre of the building or diagonal cracking if at the corner of the property. The
cracks will be larger at the bottom and thinner at the top.
Settlement — A movement down due to an increased load. Buildings will settle when first constructed or if there is a change in the load as the new load settles to the bearing capacity of the soil.
Differential Settlement — If two sections of a building are constructed off different foundations or the ground is made up of different soil types or strata then one may settle more than another
causing cracking between the two sections of the building. Most common with extensions.
Thermal movement — Either expansion or shrinkage of the masonry, is often characterised by
vertical cracks with a relatively constant width if appropriate expansion joints are not present
Lintel failure — Lintel failure allows a triangular section of brickwork above the window to drop
down creating a triangular crack from the corner of the window toward the centre.
Corroded Steel lintel — Where a steel lintel has been used above an opening and the edge is
exposed or close to the surface this can corrode over time and expand causing cracking. Cavity
wall tie failure — corrosion of large steel fishtail ties will lead to cracking every 4 or 5 courses as
the steel expand
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.
Are calcium silicate bricks deleterious?
The concern comes from the potential for movement that have given calcium silicate bricks the label of deleterious otherwise the bricks actually increase in strength when exposed to atmospheric carbon dioxide although does shrink it too. In highly polluted areas, sulphur dioxide in damp conditions causes the calcium silicate to decompose to form a gypsum crust.
What are common defects with brick slips and brick panels?
Defect - Popular in the 1960, and early 1970s, brick slips were seen as an easy method
of concealing the exposed edges of a concrete frame at each floor level. A failure to
recognise the propensity of a concrete framed building to shrink created circumstances
where the brick slips could be stressed and forced off the building, often with serious risks
to health and safety. The provision of movement joints above and below the course of
slips is essential, but great care is needed to ensure that even the smallest amount of
bridging of the soft joint does not occur. Brick panels within either exposed concrete
frames or supported on knibs can similarly be affected by unplanned shrinkage in a
concrete frame.
Remedy — Depends on the severity of the defect but in essence sufficient movement joints
are required to take account of the different movements of the different elements.
How would you recognise High Alumina Cement and in what condition would you expect to find it?
Used in buildings between 1954 and 1974. Precast pre-stressed concrete beams particularly in maritime buildings. Leaves concrete friable and sometimes browns it. Usually found in roof beams.
What are the types of damp?
Penetrating
Rising
Condensation ( + interstitial condensation)
What is a protimeter / moisture meter?
Measures the electrical resistance between two electrodes. Generally used for moisture in wood.
What is a speedy carbide meter?
Measures moisture in masonry through adding masonry dust into a container with calcium carbide which releases a gas in proportion to the moisture present.
What are the limitations of an carbide speedy meter
Destructive techniue,
Danger of fire/explosion if the regent is exposd to moisture,
Generally not as quick as other methods,
What is cold bridging?
A cold bridge is created when poor thermal insulators come into contact allowing heat to flow through the path. E.g. at the junction of a concrete slab and external walls.
How would you identify condensation? What are the remedial measures?
Generally occurs in top corners of rooms where warm air rises and collects and due to the change in temperature, the warm air releases vapour onto the colder surface. It is an issue in poorly vented and cold buildings where there is high moisture volume. It can be remedied by venting the property better and maintaining regular internal temperature.
How long would you leave brick/plaster to dry out before commencing work?
Generally should be left for 3-4 months but this is not practical.
Discolouration at 450x900mm centres in grid formation? What is the remedy?
Lateral damp ingress from defected cavity ties. Due to mortar dropping onto the cavity tie which allows moisture to penetrate through the brick. Remedy is to remove the wall tie and replace it.
What are the different ways moisture could enter the building? How would you differentiate between the types?
Penetrating – Enters via a porous bridge transferring moisture through capillary action or there might be a hole in the building fabric.
Rising – Moisture rising up from the ground through capillary action normally up to 1m high with tide marks. Usually from bridging of DPC or lack/failure of DPC.
Condensation – Warm moist air comes into contact with cold surfaces which releases the moisture. Generally at high level.
You are inspecting a building and identify several cracks in the external wall. Take me through your thought process.
Firstly, what is the building made from and what is the construction method? Are there local factors such as trees or high water tables? Have any alterations been carried out? Are there any nearby drains where the cracking is. What is the age of the building
What other sorts of cracks would you expect to see on a brick building and what might have caused them?
Subsidence – shrinkage of clay
Heave – saturated clay
Settlement – Movement from increased load.
Differential settlement – when parts of a building are constructed off different foundations or the ground has different soils, they move at different speeds.
Lintel failure – Usually leads to triangular cracking to the brickwork above the window to drop.
Internal alterations – drying of timbers or installation of steel beams without consideration of impact.
What size cracks are of concern?
BRE Digest 251
Hairline crack - less than 0.1mm wide (cat 0)
Fine Crack - Up to 1.0mm (1)
Moderate Crack - up to 5mm wide (2)
Major crack - from 5mm to 15mm
Severe - 5mm - 25mm
Very severe - more than 25mm
What are some crack monitoring techniques
Crack width gauge,
Plastic tell tale,
Glass tell tale,
Brass screws and callipers,
target and total station
What is a Crack width gauge used for
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.
What are Plastic tell tales used for
The plate with scales marked in millimeter 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 expecially if stuck on with adhesive or if knowcked. Typically 1.0mm degree of accuracy.
What are Glass tell tales used for
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.
What are Brass Screws and Calipers used for
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 calipers often have a resoloution of 0.01mm. In some cases discs are glued onto the wall.
What are targets and total station used for
Typically used to monitor larger scale movement i.e. bridge subsidance. Recorded from a known datum to ensure co Accuracy up to 1.5 at a distance of up to 1,500 meters. This can also be achived by laser reflective targets fixed to the structure. This is typically more expensive and time consuming.
Cracks between the bay window and main wall. What are the causes and remedies?
General rule of thumb is that it is caused by differential settlement due to different foundation types. It could also be because windows were swapped and the new window is not strengthened and causes the bay to drop.
What are the types of timber defects?
Insect attack
Dry rot
Wet rot
Structural defects
Describe the different types of rot and how you would recognise them?
Dry Rot – Wood shrinks and splits into cuboidal cracks. Wood is light in weight and crumbles under fingers. Usually mycelium on the surface which is grey when wet and yellow/purple when dry. Fruiting body usually brown/red in colour. Indoors only.
Wet Rot – Wood shrinks and splits. Wood darkens. Mycelium grows on surface which can be white, brown, green or amber in colour. Fruiting bodies can be different colours and occurs internally or externally.
What are the differences between wet and dry rot?
Dry Rot — Wood shrinks and splits into large cuboidal cracking, the wood is light in weight, crumbles under fingers and has a dull brown colour, cotton wool type mycelium is often visible greyish in colour when wet and yellow/purple when dry, strands are brittle when dry, a fruiting body can also occur with a reddish brown colour, only incurs inside of buildings.
Wet Rot — Wood shrinks and splits on a smaller scale, wood becomes darkened, mycelium can be white, brown, amber, green or black, strands are flexible when dry, the fruiting bodies can be a number of different colours can occur both inside and outside.
Wet rot usually caused by a source of moisture and dry is generally from condensation/humid environments.
What are the remedial measures to dry/wet rot?
Locate and remove the source of moisture and dry out the timber
Remove rotten wood plus 450mm
Apply fungicidal fluid and strengthen joists if required
What is the moisture content needed for Dry and Wet Rot?
50-60% for Wet Rot. Will not survive below 44%.
25% for dry rot
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.
Explain the life cycle of rot.
Spores – with dry rot, it is a fine orange brown dust. The spores activate when in contact with timber.
Hyphae – Timber and moisture are present, the spores will produce fine white strands which allows the rot to grow by feeding on timber.
Mycelium – Hyphae mass is known as mycelium. It grows on various materials and over vast distances which allows it to progressively destroy the structural timber.
Fruiting Body – Mushroom like form pumps spores into the air which is transferred by air currents and germinates it to create a new attack. Repeat the process
Name some common insects known to attack timber. What remedial methods are available? How long do these remedial methods last?
Category A (insecticidal treatment) – common furniture beetle, death watch, house longhorn beetle.
Category B (treatment of rotten area only) – wood boring weebills.
Category C (No treatment required) Bark borers
Remedial methods – study flight holes to identify beetles and determine if it is still active or dormant. Apply boron-based treatment to affected areas
Can you tell me the 3 most common types of woodworm in the UK?
Common Furniture Beetle
Death watch beetle
Wood boring Weevil (Less common in UK)
House Longhorn Beetle
Where are you most likely to find the death watch beetle?
Churches/old buildings with hardwood and timber suffering from fungal decay.
How do you identify the presence of woodworm?
Holes in wooden item with frass around the holes. Typically 1-1.5mm holes
How do woodworms affect timber in buildings?
Adult beetles lay eggs on the timber. The grubs feed on the timber, hatch into beetles which breed, lay eggs and the process repeats.
What is a woodworm infestation likely to indicate?
Most woodworm requires high moisture. May indicate an issue with the structure and damp.
How is a woodworm infestation treated?
Chemical insecticides. Resolve damp issue as damp wood may be re-infected
Describe the life cycle of a woodworm?
Lays eggs on the surface of the wood
Larva grows in wood crevices (Takes 1-5 years)
Pupa (Larva to adult)
Adult flights/crawls from the timber
Stage 2 is when the most damage is done to the timber
What is the lifecycle of a common furniture beetle?
Furniture beetles and longhorn – 2-5 years
Death-watch beetle – up to 10 years
Deflected timber floor in early 19th Century building. What methods are available to deal with this if the client requires a level floor?
Confirm why the floor is deflecting. Notching to joists, not adequate for spans? Inadequate support? Can the issue be remedied without destroying the floor? Supplement the joists, overboard or remove it and replace.
You find a leak at high level on a first floor of a 2 storey building constructed with traditional cavity wall construction. Please outline the process which you would go
through in assessing the cause for the defect. Also, what are the potential causes of such a defect?
I would review any existing building information available before inspecting the property. I
would look at the building as a whole to get an understanding of its construction, and the materials used, assess whether there had been any alterations to the building.
I would inspect the leak and talk to the building owner/user. I would look at the extent of the leak and the damage caused and ask questions relating to the history of the leak. When did it occur does it happen all of the time or just on occasions is it affected by the whether? I would then assess whether there were any external elements that could be the cause and then any internal elements that could be the cause. My first thought would be a roof leak so I would assess the roof both externally and internally for signs of defective or missing roof covering, defective or missing flashings around roof penetrations etc. Then when in the roof space I would look for evidence of leaking pipes.
A newly cast reinforced concrete slab is exhibiting crazing and cracking on its surface. What are the causes?
Poor or inadequate curing – environmental conditions being conducive to evaporation and lack of protection. If the mixture is too wet or excessive floating which causes aggregate to sink, the cement paste on top will start to crack.
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.
What else may have caused glazing to crack if it wasn’t nickel sulphide inclusions?
Structural movement above/below causing the frame to move or distort.
Name some sources of structural movement?
Soil shrinkage
Tree Roots
Water Table
Leaking draings/below ground services
Infill site/brownfield sites/mines
Nearby Excavations
Subsidence
How does cavity wall tile failure present itself? How would you fix it?
Horizontal cracking every 5 or so brick courses. Corrosion of old steel ties causes the cracks.
Remedy – use a borescope to determine the defect. Locate the wall ties and isolate and remove. Install replacement stainless steel mechanically fixed ties.
What is nail fatigue?
Common with slates or tiles. Nails have rusted and expanded which cracks the tile allowing them to slip. Generally, if one nail has failed, several are likely to fail too.
What would be the associated problems and defects with a “crinkly tin” shed approximately 15 years old? What defects might you find with profiled steel cladding?
Plastisol degradation
Cut edge corrosion
Defective fastenings
Why does cut edge corrosion occur? What can happen if it is not treated? How can it be remediated?
When cut edge of coated metal are exposed to elements, delamination may occur in the form of peel back of factory coating. The unprotected metal then rusts and corrodes. Can be remedied by applying a silicone paint. If the corrosion is bad, may be better to replace the panel.
What coatings are usually found on sheet metal? How can it break down?
Plastisol is a PVC coating. Usually has a leather effect. Or use PVF2 which is a thinner material with a smooth finish. These are both effected by temperature, UV exposure which can lead to caulking and delamination.
What typical defects are found in 60’s/70’s commercial buildings?
Asbestos
Concrete defects
Cold roof
Wood wool slabs
What kind of defects did you find in industrial buildings?
Cut edge corrosion
Plastisol degradation
Asbestos use in insulation
What is concrete carbonation?
Carbonation occurs due to the ingress of atmospheric carbon dioxide reacting with water within the concrete, which forms carbonic acid that neutralises concrete alkalinity
This breaks down the passive layer around the reinforcement causing it to corrode due to the presence of water and oxygen. This happens at a slow rate (progressive)
Carbonation is more of a concern where there is poor or shallow cover over the steel reinforcement, or the concrete is poorly compacted
Carbonation is more rapid in porous concrete with low cement content and concrete with high water to cement ratio
How would you identify concrete carbonation?
Occurs to reinforced concrete buildings and structures – it is inevitable
Fine cracks appear in the concrete causing the reinforcement to corrode
Hairline cracks appear along the reinforcement line
The reinforcement expands due to the rusting
Concrete spalls and cracks exposing the reinforcement
Explain the testing procedure when testing for concrete carbonation
Apply a solution to the concrete that can highlight any areas of carbonation in the concrete
What are the remedial measures for concrete carbonation?
Replacement – this involves removing defective concrete and cutting out the reinforcement to damaged members. New reinforcement is fixed but welding to existing and new concrete is cast. This is the simplest method and completed by specialist contractors.
Gunting – a propriety process in which fine concrete is sprayed onto a concrete surface under repair of high velocity.
Coating – coatings, sealants and membranes can be effective in reducing the carbonation process. however, if chloride is present at rebar depth then the coating will not prevent carbonation.
Electrochemical re-alkalisation – the cathodic reaction around rebars produce hydroxyl ions. The steel cathodes also attack alkali metal ions towards its surface, so high alkalinity is restored around rebar. A temporary anode (steel mesh) is attached to concrete, the electrolyte penetrates the concrete and raises the alkalinity at the cover. An anti-carbonation coating is applied.
Cathodic protection – this is a permanent and very expensive technique. an anode system (coating or mesh) are sprayed or fixed to the whole surface of concrete. A current is applied which passes to the reinforcement, which is then made cathode preventing corrosion of the reinforcement.
What is HAC High alumina cement?
High Alumina Cement was used in the production of pre-cast concrete sections. This has very high strength at an early stage, however, loses strength as it ages and is susceptible to chemical attack in damp conditions.
Introduced in 1925, cement producer Lafarge commenced the UK manufacture of High Alumina Cement to provide concrete that would resist chemical attack, particularly for marine applications. Used in the UK from 1950-1976 in the manufacture of pre-stressed concrete beams
What are the problems with HAC?
HAC concrete undergoes a mineralogical change known as conversion. During this process the concrete increases in porosity which in turn results in a loss of strength and reduction in resistance to chemical attack. The higher the temperature during the casting of the concrete the more quickly conversion takes place.
Remedial measures for HAC?
An investigation should be undertaken consisting:
Sample testing
Collect details of construction materials used – the local authorities hold records of HAC buildings
If the strength has been reduced – reduce the live loads or strengthen
In the case of reinforcement corrosion – localised repairs can slow further deterioration
What is Alkali silica reaction?
Occurs where the chemical within the cement react with silica (in aggregates), forms a gel substance which absorbs water and expands creating cracks where water can enter. Further cracking may occur as a result of water freezing within the cracks.
* Cracking
* Small pop outs
* Map cracking
* Tensile strength reduced
* Gel absorbs water causing further cracking
* Cracks run parallel to reinforcement bars
What are the ASR remedial measures?
Remove one of the following and ASR will not take place:
Critical silica in aggregate
Sufficient moisture
High alkalinity
Use low alkali cement and avoid use of chemically reactive aggregates
Consider complete replacement of an ASR affected section to maintain integrity and safety
What is Chloride attack ? (salts)
Chlorides may either ingress (from penetration of de-icing salts) or cast insitu as sea dredged aggregates or calcium chloride additive.
Chloride ions attack the reinforcement can cause:
In certain circumstances ‘pitting’ corrosion can occur – when the steel is effectively eaten away without the formation of expansive rust
Corrosion of steel reinforcement is localised compared to carbonation and much more rapid.
Spalling of concrete
Significant loss of cross-sectional area
Pit in bar surface – rebars could be completely eaten away
Visual sign of cracking and spalling following expansive rusting
Remedial measured for chloride attack?
Cathodic protection
Corrosion inhibitors
Epoxy resin repairs
What is subsidence?
The downward movement of the site/ground where a building stands
Can also be associated with Heave
How do you identify subsidence?
Identified by diagonal cracking which is usually tapered (of uneven width) in the buildings structure/façade and verified by leaning or pulling of the building. Subsidence usually shows up as cracks that are typically wider at the top than the bottom. They commonly appear around windows, doors and other weaker areas. Doors and windows may stick when opening them, walls and floors may show signs of distortion.
Name some causes of Subsidence?
Tree extracting water
shrinkable clay ground
mining activity
Remedial works for subsidence?
Refer to BRE guidance to understand how to assess damage.
Remedying the source of the problem can be effective, however it can sometimes make things worse i.e. removing a tree causes moisture to return = heave
Underpinning is an option but it is expensive and disruptive
Use pneumatic jacks to lift the building and reverse the movement
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.
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 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
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 single-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 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 methods are there for assessing roof defects?
Visual
Electronic leak detection
Thermographic examination
What should you consider when deciding whether to repair or replace a flat roof?
Its age and life expectancy, the overall condition i.e. are the defects localised or affecting the
whole of the roof, what type of defect is it and does it relate to a localised factor or is it an
issue with the whole roof, are they affecting the surface layer or the roof structure. Client’s
intentions for the building, their budget, the building use, disruption caused and possible
phasing required?
* Age
* Condition
* Extent of Defect
* Cost
* Use
* Life Cycle Costing
* Disruption associated with repair and replacement.
Talk me through how you inspected a flat roof
Firstly gather historical building information and details of any current or previous issues with
the roof. Make arrangements for access and prepare necessary RAMS.
Firstly identify:
* Age
* Previous repairs
* Period defective for
* When does it leak
* Does water pond
* Use of room below
* Used as a balcony or terrace
* Access arrangements
Secondly carry out a visual inspection during or after rain
How would you identify condensation in a property?
Mould growth
Any stains or streaks of water
dampness behind furniture/inside wardrobes etc.
What is interstitial condensation?
Where condensation is formed within the fabric of a building
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.
Are there any limitations with the use of a damp meter?
Most are calibrated for timber and can’t give accurate readings for other materials. Measures can be affected if timber has been treated with waterbased preservatives and the temperature of the wood can also effect readings.
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.
What does passivity mean?
Passivity is generated by the buildup of a layer of metal oxide on the surface of a metal. In order to provide passivity, this oxide layer must be stable. It is formed by corrosion insoluble components in the immediate environment of the metal. The metal oxide acts as a barrier by separating the metal’s surface from its environment and prevents corrosion until the reactants are able to diffuse through the oxide film. This diffusion may take a significant time to occur.
Flank wall bulging full over its full height. Possible causes?
A possible cause is the lack of lateral restraint in the wall. If the floor joists are running from the
front to the back of the house then there may be nothing connecting the flank wall to the building at the first and second floor levels. This may be due to poor design or some alteration in the internal layout such as a change in position of the staircase. Other potential causes to consider include cavity wall tie failure or increased roof load.
Foundations can subside or heave. Name some reasons.
Heave — Usually in cohesive soils such as clay. Possible causes include removal of trees, change in water table, leaking drains or inadequate foundations that are built within the movement zone.
Subsidence - In all soil types. Differences in the type of soil leading to differences in the bearing capacity, a change in the water course or high water course, defective drain, voids in ground
collapsing. Growth of trees removing water from the soil.
Give some examples of high-water demand trees.
Elm, Oak, Poplar, Willow trees
What do you understand by the phrase “tree root moisture extraction”?
how much water trees take in/require from the ground which can affect soil and cause subsidence, and potential heave when a tree is removed.
Provide an example where you have identified window defects. Explain what they were and what your saw during your inspection.
Missing or broken handles
Windows that don’t close (faulty hinges)
Rotten sills
glass fogging in double glazing (broken/aged seals allowing moisture into the pane)
broken glass
What is included in the readers digest 361 ‘why do buildings crack’ publication?
Causes of cracking in buildings and the results of the problems. Broad understanding of crack diagnosis and repair.
Name some principle causes of cracking?
Physical Changes (i.e. efflorescence, temp changes, shrinkage)
Chemical Changes (i.e Sulfate attack, carbonation, alkali silica reaction)
Imposed Load Effects (structural loading)
Differential Soil Movements (settlemen, mining, land slips)
Vibration (traffic, machinery, mining, explosions)
What is included in the readers digest 251 ‘assessment of damage in low rise buildings’ publication?
This Digest discusses the assessment and classification of visible damage resulting from structural distortion. The assessment is based on a description of work considered necessary to repair the building fabric; classification into six categories is recommended, taking into account the nature, location and type of damage.
How would you determine the age of cracks?
This can be done by questioning the occupants on the date of discovery and by examining the fracture surfaces, particularly of external cracks, for signs of age. For instance, recent cracks in brickwork have a clean appearance, whereas older cracks show signs of dirt accumulation.
How do you classify the damage caused by cracks under Digest 251?
3 Broad categories ‘Aesthetic’, ‘Serviceability’ and ‘Stability’. and category from 0 - 5. (0-2 is aesthetic) 3&4 (serviceability) and 5 (stability).
0 Hairline cracks of less than about 0.1 mm which are classed as negligible. No action required.
1 Fine cracks which can be treated easily using normal decoration. Damage generally restricted to internal wall finishes; cracks rarely visible in external brickwork. Typical crack widths up to 1 mm.
2 Cracks easily filled. Recurrent cracks can be masked by suitable linings. Cracks not necessarily visible externally; some external repointing may be required to ensure weather-tightness. Doors and windows may stick slightly
and require easing and adjusting. Typical crack widths up to 5 mm.
3 Cracks which require some opening up and can be
patched by a mason. Repointing of external brickwork and possibly a small amount of brickwork to be replaced. Doors and windows sticking. Service pipes may fracture. Weather-tightness often impaired. Typical crack widths
are 5 to 15 mm, or several of, say, 3 mm.
4 Extensive damage which requires breaking-out and replacing sections of walls, especially over doors and windows. Windows and door frames distorted, floor
sloping noticeably. Walls leaning or bulging noticeably, some loss of bearing in beams. Service pipes
disrupted. Typical crack widths are 15 to 25 mm, but also depends on number of cracks.
5 Structural damage which requires a major repair job, involving partial or complete rebuilding. Beams lose bearing, walls lean badly and require shoring. Windows broken with distortion. Danger of instability. Typical crack widths are greater than 25 mm, but depends on number of cracks.
Cracking causes associated with the structure include
material shrinkage and creep;
corrosion or decay;
differential thermal movements in dissimilar materials;
poor detail design or workmanship.
Cracking causes associated with the ground include:
- ground subsidence and heave due to volume changes in clay soils;
- settlement and heave of floor slabs on unsuitable or poorly-compacted in-fill beneath the slab;
- instability of sloping ground;
- movement due to consolidation of poor ground or made-ground;
- mining subsidence;
- movement caused by nearby excavations;
- chemical attack on foundation concrete or erosion of fine soil particles due to the passage of water, for example from a leaking pipe. Also included is differential settlement induced by unequal foundation pressures arising from such factors as extensions added to existing buildings or concentrations of load, for example under chimneys.
What is mine fungus
Mine Fungus (also known as fibrovaillantii). A form of wet rot often mistaken as dry rot. The fungus grows on coniferous trees such as pine. The fruiting body is an irregular white plate with a thickness of 2-12mm. White cotten like mycelium can grow, in newly formed mycelium fine drops of clear liquid maybe present.
What is ground heave?
What is Ground heaveGround heave is the upward movement of the ground usually associated with the expansion of clay soils which swell when wet.
What are causes of ground heave
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.
What are some signs of ground heave
Vertical cracking to brickwork and windows.
Doors sticking as their frames become out of square.
Lifting of paths and patios surrounding buildings.
What are some Preventions and remedies for ground heave
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.
What is Sick Building Syndrome
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
What is the cause of Sick Building Syndrome
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
What is thermal expansion
Oversailing of DPC
Buckling or bowing of walls
Fracture of the masonry units
Fracture of an outer cavity wall with no joints
What is a DPC
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.
What are some common issues with a DPC
DPC across the cavity instead of a cavity tray
Missing DPC at corners where the cavity trays meet
Not vertical protection where cavity trays step down
Raised ground level above DPC
Rendered over the DPC
What types of DPC are there
Slate
Membrane
Engineering brick
What are some features of a Tudor house
Elizibeithan / 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 chimneys
Glazed windows widely used. Glass is small and imperfect.
2nd floor typically overhangs the first
Roofs typically relatively steep
How does water enter buildings
Condensation
Penetrating dampness
Rising dampness
Leaks (e.g. from pipework)
Trapped construction water (new builds)
Describe the main consequences caused by dampness within buildings.
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
What is Gravimetric Testing
A sample is weighed, dried in an oven and then weighed again
Moisture content = (wet weight - dry weight x 100) / dry weight
What is meant by the term ‘dew point’
Dew point - the temperature at which the air becomes saturated and will condense
What is meant by the term ‘relative humidity’
Relative humidity - moisture content present within the air, referred to as a percentage of the amount of water vapour it can hold at that temperature
How would you identify condensation within a building?
Wall has a ‘misty’ surface
Stains or streaks of water running down a wall (particularly in bathrooms, kitchens and below windows)
Damp patches with no definitive edges
Dampness behind wall cupboards or inside wardrobes against external walls (areas where air circulation is restricted)
Localised dampness at potential ‘cold bridges’
Patches of mould growth
Humidity (measured using a hygrometer), insulation and ventilation levels, as well as heating and living patterns, must also be taken into account
What steps would you recommend to eliminate condensation?
Reduce moisture generation (lids on pans, dry clothes outside, vent tumble dryers externally, do not use paraffin or bottled gas heaters, put cold water in bath before hot)
Increase ventilation to remove moisture-laden air (open trickle vents, open windows, mechanical ventilation)
Increase air temperature by heating - warmer air can hold more water vapour without condensing
Increase surface temperature by thermal insulation (external or internal)
