Builiding Pathology Flashcards
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 can you identify a woodworm infestation?
Flight holes - sizes - are they recent or historic?
Death watch beetles can make a tapping noise
Fresh bore dust on flight holes
Are there any insects in spider webs?
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
How long can the common furniture beetle live in wood?
up to 4 years
Name some causes of penetrating damp
Roof Leaks, internal leaks, blocked gutters, raised ground levels
When did DPCs become compulsory?
1875 became compulsory in London (late Victorian)
As part of the public health act 1875
What is subsidence?
The downward movement of the site/ground where a building stands
Can also be associated with Heave
Name some causes of Subsidence?
Tree extracting water
shrinkable clay ground
mining activity
Common signs of Dry Rot?
Damaged Timber
Concentrated spore dust
fruiting bodies
What is Efflorescence?
Visible on brickwok and caused by soluble salts being brought to the surface as the wall dries out.
Shown as White Staining
Which BRE Digest covers ‘Wet Rot’?
345
How can you remedy ‘Wet Rot’?
Identify and eliminate all sources of moisture and promote drying
Where required, replace damaged wood.
Apply localisted preservative treatment.
What is the typical life cycle of wet rot?
Spores Germination Hypha Mycelium Fruiting bodies Repeat
What is regents street disease?
Defect - Regents Street Disease/ Deansgate Dilema occurs in buildings constructed
using a steel frame covered in facing masonry or stone. Often found in early twentieth
century buildings where large masonry or stone units were tightly built around the
steel frame. These porous materials allow moisture to get to the steel structure which
then corrodes. Corroded metals can increase up to 7 times their original size. This
puts pressure on the surrounding masonry causing cracking.
Identification — Cracking to masonry around the structural frame.
Remedy - Today there are two repair options available to address this problem.
What is Carbonation?
Defect — 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.
Inadequate coverage, mix proportions cpmpaction. Temperature, humidity and CO2
levels can all affect the level of carbonation.
The rate at which carbonation occurs is inversely proportional to the square root of the
age of the building i.e. typical Portland cement concrete may show a depth of
carbonation of 3-5mm after 10 years.
Identification -A simple on site test can be carried out by using a simple alkali-sensitive
staining technique. Phenolphthalein will turn purple on unaffected concrete where it is still
highly alkaline. No staining is observed where carbonation has reduced the level of alkalinity.
A more robust technique is through petrographic analysis where a sample of the concrete is
examined under a microscope.
Remedy — How is carbonation remedied?
Typical remedy is to remove the delaminated concrete, clean the re-bar by abrasive blast
cleaning and patch in the concrete. A longer term and more expensive solution is to induce
cathodic protection. This is where an external anode is connected to the metal and the
passage of an electric current is used to stop corrosions.
What is Chloride Attack?
Defect - Calcium Chloride Additive — Used as an accelerator mainly in the 1950’s and
1960’s (it was banned in 1977). Reduces the passivity of the concrete in damp conditions
leading to corrosion in the form of localised pitting of the rebar. The inclusion of calcium
chloride ion into concrete increases the electrical conductivity of the concrete and with this,
the likely corrosion rates. Sufficient quantities of chloride ion can disrupt the passive layer
around steel reinforcement, and if they exceed a threshold level can prevent the passive layer
from being re-established.
However, whilst chlorides are no longer added to concrete as an admixture, they could
still be present as a result of poorly washed marine aggregates, or from exposure to deicing
salts, salt spray, sea water and the like. Chlorides can be absorbed into the body of
the concrete by processes of absorption and diffusion. Potentially, concrete affected by
external contamination sources is likely to be at more risk of corrosion
Identification — Rust staining and delamination of concrete. Examination of the reenforcement
bar will show signs of pitting where localized breakdown of the passive oxide
layer has occurred. Occasionally the rebar may be completely eaten away leading to
obvious structural concerns.
Remedy - Localised concrete repairs can be carried out, however if the original mixture
includes chlorides then it is likely that the corrosion will commence in another area. A longer
term and more expensive solution is to induce cathodic protection. This is where an external
anode is connected to the metal and the passage of an electric current is used to stop
corrosions.
What is Alkiali Silica Reaction?
Defect - Alkali silica reaction (ASR) is the most common form of alkali-aggregate
reaction. Concrete is a highly alkaline material and therefore any pore water within the
concrete will also be alkaline. In certain situations the alkaline water can react with the
silica in the aggregate to produce a gel. The gel takes in water, expands and can cause
concrete to crack or disrupt.
Identification - In unrestrained concrete, the cracks have a characteristic random
distribution often referred to as ‘map cracking’. In restrained concrete, the cracking tends
to run parallel to the main reinforcing bars. In particularly active situations, the cracks may
be bordered by a colourless gel. This leads to surface pop-outs and spelling. Petrographic
examination is the only sure way of identifying the attack.
Remedy - Three conditions are necessary for ASR to occur: certain silica in the
aggregate, sufficient moisture, high alkalinity. Removal of moisture by repairing damaged
rain water goods is the first measure. Removal of the delaminated concrete and an
isolated patch repair may also be an alternative. Secondary structural reinforcement can
also be introduced.
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.
What is sulphate attack?
Defect - Sulphate attack is a chemical reaction affecting concrete causing it to expand
and crack. Externally, this is due to penetration of sulphates in solution (i.e. in
groundwater) into the concrete from outside. Internally, this is due to a soluble source
being incorporated into the concrete at the time of mixing (i.e. gypsum in the aggregate)
or sulphates within the hardcore beneath the concrete. This can lead to heave of the slab
and structural damage.
Remedy - It is often the case that the concrete will need to be dug up and replaced with a
sulphate resist concrete.
Name some defects associated with flat roofs?
Crazing - from exposure to the sun or occasionally chemical attack.
Ponding - Standing water can reduce lifespan
Thermal Movement - Cracks, splits and rucks can occur.
Blistering - caused by water vapour pressure occuring below the roof covering.
Flashing and Falls around openings - poor workmanship or deterioration of flashing details.
Punctures by people/impact damage
What is the minimum fall for a flat roof?
1:40. Best practice more like 1:60
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
What is damp?
A building is only considered damp if the moisture becomes visible through discoloration and staining of finishes or causes mould growth, sulphate attack, frost damage or drips/puddles.
How do you test for damp?
The use of a protimeter I moisture meter or a Speedy Carbide Meter can be used to establish
the moisture content of walls, and the level of damp occurring.
What is a protimeter / moisture meter?
A protimeter works by measuring the electrical resistance between two applied electrodes.
Protimeters are generally used to monitor the moisture content in wood, therefore when used
on other materials, the actual readings may be misleading but does give a sense of moisture
content.
What is a Speedy Carbide Meter?
A speedy carbide meter is a device to measure moisture in masonry through slow drilling
masonry and putting dust into a sealed container with a known measurement of calcium
carbide. It releases a gas in proportion to the amount of moisture present
How would you identify rising damp? What are the causes? How would you remedy it?
RISING DAMP - -Inn high tide mark, peeling and blistering of wall finishes, musty smell, rotting of
timber, hyproscopic salts. Use of Speedy carbide meter to measure moisture. The readings with
moisture meter result in high surface readings, often with slight decline, finishing with a sudden cutoff
CAUSES — No damp proof course, DPC bridged by pointing, render, soil, paving, mortar
droppings, affects both solid and suspended floors.
REMEDY — Remedy DPC problems, remove bridging of DPC, chemical injected DPC
Penetrating damp can often be misdiagnosed as rising damp and should be careful.
How would you identify penetration damp? What are the causes? How would you
remedy it?
PENETRATION DAMP — dependant upon the levels of exposure of the building and often
penetration only occurs in certain areas. The first sign of damp penetration is often the
appearance of damp patches on walls, ceilings or floors. These tend to grow or darken after
periods of heavy or prolonged rain.
CAUSES — Rain driving through exposed masonry walls that have insufficient thickness,
problems with cavity trays, cracked or detached rendering, defects to window cills, blocked
cavity ties
REMEDY — Repointing of defective mortar joints, apply masonry water repellent, make good
defective joint details, inspect cavity tray and cavity ties for blockages, inspect areas of roofs such
as chimneys, parapets and thresholds
What is a cold bridge?
A cold bridge is created when materials that are poor thermal insulators come into contact,
allowing heat to flow through the path created, although nearby layers of material separated by
airspace allow little heat transfer. Insulation around a bridge is of little help in preventing heat
loss or gain due to thermal bridging; the bridging has to be eliminated, rebuilt with a reduced
cross-section or with materials that have better insulating properties, or with an additional
insulating component, called a thermal break.
How would you identify condensation? What are the causes? How would you remedy it?
Causes - Condensation is caused by hot air carrying moisture hitting a cold surface and the
moisture condensing on that surface. It is an issue in occupied premises often in areas of
cooking or bathing. It can lead to staining, peeling of surface finishes and mould growth at cold
bridging points.
Remedial Measures - Provide mechanical ventilation to the affected spaces, reduce moisture
generation, provide adequate heating, install insulation or thermal breaks to remove the cold
bridges.
Discolouring @ 450 x 900mm centres in a grid formation? Remediation?
This describes lateral damp ingress, from defective or blocked cavity ties. This is usually due to
mortar dropping onto the cavity tie, thus making the drip ineffective. This allows penetration damp
to occur.
What is interstitial condensation?
Where condensation is formed within the fabric of a building
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.
What sorts of cracks would you expect to see on a brick building and what might
have caused them
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 expands
In BRE Digest 251 (Assessment of damage to low rise buildings), what are the severity of cracks defined as?
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 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.
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.
What types of timber defects are there?
The main timber defects are dry rot and wet rot, insect attack
Describe the different types of rot and how you would recognise them.
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.
What are the remedial measures to dry/wet rot?
Locate and eliminate the sources of moisture, promote rapid drying, remove rotted wood
(450mm beyond last indications of rot and burn), surface application of fungicidal fluid,
introduce support measures if required.
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?
Typical indications of dry rot include:
• Wood shrinks, darkens and cracks in a ‘cuboidal’ manner.
• A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow
often develops under less humid conditions. This ‘skin’ can be peeled like a mushroom.
• White, fluffy ‘cottonwool’ mycelium develops under humid conditions. ‘Teardrops’ may develop on the
growth.
• Strands develop in the mycelium; these are brittle and when dry and crack when bent.
• Fruiting bodies are a soft, fleshy pancake or bracket with an orange-ochre surface. The surface
has wide pores.
• Rust red coloured spore dust frequently seen around fruiting bodies.
• Active decay produces a musty, damp odour.
• Only occurs in certain conditions with 20-40% moisture content.
Therefore identifying and removing the cause of moisture is key to eradicating the rot. Any
affected timbers should be removed and replaced with pre-treated timber. Any remaining
timbers at risk of being affected by the dry rot should be treated with an effective fungicide.
Where the dry rot has passed through the masonry, it should be isolated using physical
containment and/or masonry sterilisation.
Ends of the joists in a timber floor built in an external wall have been seriously affected by
wet rot. How will you recognise this type of rot and what action would you take to resolve
the problem?
Wet Rot requires high moisture contents of around 50-60% to propagate and spread, it is
usually found in areas where there may be a water leak, or building failure, such as along
window cills and in roof voids.
Indications of a Wet rot outbreak include:
• Surface cracking — cracks follow timber grain.
• Hyphae strands are thread like brown, yellowish, becoming darker brown in colour. (Key
difference distinguishing from Dry rot)
• Distinctive fruiting body — (Although rarely found), thin sheet like shape, knobbly and olive brown
surface.
• Infected timber turns dark brown in colour
The first step to remedying Wet and Dry Rot is to find and eliminate the source of dampness,
rectifying those faults that have contributed to the problem to prevent timbers becoming damp. Wet
Rot
All infected and/or damaged timber should be removed, as these may be structurally impaired
due to the decaying action of the Wet Rot and the remaining timber treated with a suitable
preservative.
If the Wet Rot is in a confined space, such as a cupboard or loft space, it may be necessary to
consider methods to improve the ventilation
What are the remedial measures for Dry Rot?
Remedial action for Dry Rot is far more intrusive. The first step is to establish the full extent of
the outbreak, many parts of which may be initially concealed from view, underneath
floorboards, behind furniture, panels removed etc.
Affected timber, similar to Wet Rot needs to be cut out and replaced, including those within
approximately 300-450mm beyond, to allow for possible further contamination. All surrounding
timbers should be treated with a chemical biocide, to ensure all strands/ spores are killed off. It is
imperative, that you ensure the timbers do not become re wetted at this stage, as this would
invalidate any insurance or guarantee for the Dry Rot treatment.
Affected plaster that has come into contact with the Dry Rot needs to be removed, and wall
surfaces treated with a sterilizer or biocide.
Lastly, the area should be kept dry and heated, to ensure all timbers are fully dried out to
prevent or reduce the likelihood of further outbreaks.
Name some common insects that are 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 beetle and house
longhorn beetle
Category B (treatment only necessary for associated rot) — wood boring weevils
Category C (No treatment needed) — Bark borers
Remedial measures — study flight holes to identify beetle and determine if the infestation is still
active or dormant, apply two coats of boron based treatment to all affected areas going at least
300mm onto the sound timber, if severe attack then replacement of the damaged timber with pretreated
wood is required.
How do you identify the presence of woodworm?
Holes in the wooden item, with live infestations showing powder (faeces) around the holes. The
size of the holes varies, but are typically 1nnnn to 1.5mm in diameter for the most common
household species. Adult beetles which emerged from the wood may also be found in the
summer months.
How do woodworms affect timber in buildings?
Typically the adult beetles lay eggs on, or just under the surface of, a wooden item. The resulting
grubs then feed on the wooden item causing both structural and cosmetic damage, before
pupating and hatching as beetles which then breed, lay eggs, and repeat the process causing
further damage.
What is a woodworm infestation likely to indicate?
Most species of woodworm require that the wooden item contain a higher moisture content than is
normally found in wooden items in a typical home. A building with a woodworm problem in the
structure or furniture probably/possibly also has a problem with excess damp.
How is a woodworm infestation treated?
Woodworm infestation is generally controlled with chemical insecticides. However, it is also
advisable to investigate and solve possible damp issues, as dry wood is not usually affected, and
wood that remains damp may be re-infected at a later date.
What is the life-cycle of a common furniture beetle?
Common furniture beetles and longhorn beetles (2-5 years), deathwatch 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 the cause of the deflection, notching, rot, insufficiently sized joists, insufficient centres,
overloading, deterioration of sleeper walls etc. Confirm if issue can be remedied and timber floor
retained. Potential to supplement the timber joists, potential to overboarded, potential to remove and
replace with suspended timber floor or alternative solid floor.
A newly cast reinforced concrete slab is exhibiting crazing and cracking on its surface.
Possible causes?
Poor or inadequate curing — cause by environmental conditions being conducive to high
evaporation rates and a lack of adequate protection.
To wet a mix, excessive floating or use of a jitterbug or other procedures that will depress
the coarse aggregate and produce an excessive concentration of cement paste and fines at the
surface.
Finishing operations performed while bleed water remains at the surface and other
finishing procedures that produce a high water cement ratio at the surface.
Sprinkling cement on the surface to dry up the bleed water.
Name the three types of asbestos and examples of where they are found in buildings.
Chrysotile - the most common form of asbestos found in buildings. The most common use is
within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and
garages.
Amosite - is found most frequently as a fire retardant in thermal insulation products and ceiling
tiles
Crocidolite
What are Nickel Sulfide Inclusions?
Inherent in the glass production process are microscopic imperfections in the glass, known as
inclusions. Most of these are completely harmless, but nickel sulfide (NiS) inclusions have been
shown to cause disastrous failure of tempered glass. When annealed (aka float) glass is heated
in the tempering process, so are any NiS inclusions present in the glass. However, when the
glass is rapidly cooled to achieve the properties of tempered glass, the NiS remains in a high -
temperature form. Over several years, the NiS will return to its low-temperature state, and in the
process will increase in volume. This can cause cracking and additional tensile stresses which,
in tempered glass, have lead to spectacular failures with no visible cause. This phenomenon
has also been referred to as “glass cancer” and “spontaneous glass failure”.
What else may have caused glazing to crack if it wasn’t Nickel Sulphide Inclusions?
Structural movement around the window opening could have put pressure on the glazing and
caused the crack.
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.
How does cavity wall tie failure present itself? How would you fix it?
IDENTIFICATION — Horizontal cracking in every 5 or so brick course or in render. It’s the corrosion
of old steel ties such as large fishtail. The corrosion increases the steel up to 4 times leading to the
cracking.
REMEDY — use boroscope to determine the defect is wall tie failure. Locate wall ties and isolate or
removed to ensure no further damage. Install replacement stainless steel mechanical fixed ties
secured with an epoxy resin if required
