Building Pathology Flashcards
What is settlement ?
Settlement is the downward movement of the ground caused by a load consolidating the soil below it or causing displacement of the soil.
What is sulfate attack in concrete?
A reaction between the concrete and the ground bearing slab where the presence of sulphates are within the hardcore/soil or introduced via water.
This creates a new compound that expands within the concrete to cause cracking.
Testing can be carried out via samples of the concrete and sub fill material.
Can take several years to come to fruition and is linked to coal mining areas.
Measures introduced include the selection of suitable materials, inclusion of a dpm.
What is the Latin for dry rot ?
Serpula lacrymans
What are the two forms of measurement provided by the protimeter?
Prongs = WME - Wood moisture equivalent.
Surface reading = Measured to a depth of about 19mm and a measure from 0-999
What may give you false readings from a protimeter ?
Foil backed plasterboard
Salts within the brickwork.
Free water in brickwork.
Can you give me some examples of causes of movement in buildings?
Subsidence, Heave, Thermal/shrinkage, structural failure.
What are the ideal conditions for dry rot to spread?
Dry Rot requires wood as a food source. The fungus grows most rapidly on wood that has a moisture content around 20% though not saturated.
Dark, damp and poorly ventilated spaces are ideal conditions.
For dry rot how far past the affected timber would you remove?
BRE digest 299 suggests 300-450 mm past the affected area.
Treat surrounding timber with preservatives.
If affected structural timber seek guidance from a structural engineer.
Sometimes it is necessary to seperate vulverable timbers frim ‘infected’ masonry.
Can you expand on BRE 251?
This defines cracks and assessment of cracking from level 0, a hairline crack less than 0.1mm, up to structural damage cracks greater than 25mm.
The digest also recommend relevant remedial actions.
What is subsidence?
The downward movement of ground due to chnages within the sub-soil.
This can be affected by the proximity of trees and drains or seasonal variations.
What is frost heave?
Upward movement of the ground caused by water within the sub soil freezing and expanding.
Is common in places with high water tables.
What are shrinkable clays?
Clays that are capable of absorbing and releasing large amounts of water, which can affect foundation movement.
How can the removal of trees affect foundations?
Once a tree is removed, the sub soils absorb water that would have previously been absorbed by the tree. The sub soild expand and lead to ground swell or ground heave which can affect foundations.
What is wall tie failure and how would you identify 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 borescope 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
What are the different types of rot and how would you identify them?
Dry Rot – Wood shrinks and splits into cuboidal cracks. Wood is light in weight when rot has taken hold ends up dry and crumbles under fingers. Usually mycelium on the surface which is grey when wet and yellow/purple when dry. cotton wool like/leathery skin. 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, but rare and occurs internally or externally.
Can you expand on what trada tables are please ?
TRADA’s Span tables have been in existence for decades now, helping designer and builders quickly look up the right sized softwood members for domestic projects.
What are the stages of dry rot ?
Spores
Hyphae
Mycelium
Fruiting Body
What are the different types of common damp in buildings ?
Condensation
Rising damp
Penetrating damp
How would you identity between dry and wet rot?
Dry rot is the most serious form of fungus decay in a building, spreads onto and destroys much of the timber.
On the other hand, the wet rot fungus occurs more frequently but is less serious, the decay is usually detained to where the timber becomes and stays wet.
The Wet rot fungus tends to grow on porous surfaces, for example, timber with a high moisture content of around 50% while for dry rot to grow moisture of around 20% needs to be present.
If left untreated wet rot can cause major structural problems as it can lead to weakened timbers.
For moisture content to be suitable for wet rot growth there has to be a source of constant moisture – this could be as a result of defective plumbing or damaged guttering.
Wet rot cannot spread through masonry and will cease to grow when the source of moisture is taken away.
Due to the parts of the building that tend to have the correct moisture levels, for example, underfloor areas, dry rot can often cause significant damage before the homeowner is aware that there is even a problem with dry rot in the property.
What are wood boring insects and where can they usually be found?
A wood boring insect is a common term that covers many species of beetles that as larvae eat and destroy timbers.
Wood boring insects are usually found in areas within a property that are poorly ventilated with a high humidity such as for example a sub floor crawl space.
This is usually because these conditions become perfect for the larvae to hibernate and transform into a woodworm beetle.
What are the the limitations of a protimeter?
Calibrated for timber only.
They are used to verify visual inspections and cannot be relied upon.
What is a borescope and how do you use it?
A small instrusive camera used to inspect hard to reach areas.
Normally required to make a hole to view into a cavity as an example.
What is fungal attack and what are the effects?
Fungi that attack timber in buildings. The effects can be loss of strength, loss of weight, change in colour.
What is the moisture content in timber, required for dry rot?
Timber requires a moisture content of around 20/22% before dry rot can develop.
How can you identify dry rot?
Dry rot can appear in a variety of ways, depending on the stage of the infestation. Here are some signs of dry rot:
Mycelium: A white, cotton-wool-like substance that develops on the wood. It can also have grey or white strands.
Skin: A grey-whitish or silky skin that can be peeled off like a mushroom. It may have patches of lilac or yellow.
Cracks: The wood may crack in a cuboidal pattern. It will be dry and crumbly.
Darkening: The wood may darken in color.
Shrinking: The wood may shrink.
Fruiting bodies: A soft, fleshy, mushroom-like body that is often orangey in color with a rust-colored center.
Spores: Rust-colored spores that can be found in the affected area or around fruiting bodies.
How does Dry Rot spread?
Dry rot produces strands within the mycelium which feed the growth area.
The strands can travel over or through inert materials in the search for food.
What are the environmental conditions for Wet Rot?
Wet rot, a type of fungal decay, typically grows in timber with a moisture content of around 30–50% and generally requires a consistent source of moisture.
Wet rot can be caused by a number of things, including: Leaking roofs or gutters, Plumbing leaks, Condensation in poorly ventilated areas, and Rising damp.
What are the effects of Wet Rot?
While it’s generally considered less serious than dry rot, wet rot can still weaken structural timbers and cause major damage if left untreated.
Wet rot is also different from dry rot in that it’s usually confined to a damp area and doesn’t spread, while dry rot can spread beyond its initial germination site.
How did you know that it was Wet Rot, in the loft area of Ditton Hill Road?
Within the loft there was a clear damp musty smell. When I saw the affected area, it was visually darker than the surrounding timbers. I tested this with a protimeter and the moisture content was around 50% and the timber was spongy in areas.
How did you advise the client to deal with the wet rot?
As I had located the cause, which was the failure of the lead valley gutter and detailing to chimney stack, I advised that this required addressing to eliminate the source.
The affected timbers should then be treated to prevent rot speading. A wood hardener could be used for timbers that were salvagable. However, any structurally affected timbers should be replaced.
I also advised the client to install additional ventilation tiles within the roof, to improve ventilation in the loft space.
What is the life cycle of an insect attack on timber?
Adult insect lays egg.
Larvae hatch.
Larvae tunnel into wood, eating it on their way.
Pupa forms.
Adult emerges through exist hole.
What are some common conditions for insect attack?
Insects generally tend to attack sapwood, rather than heartwood.
Usually in areas of dampness or with little ventilation.
What types of wood boring inspect might you expect to find in domestic dwellings in the UK?
Common Furniture Beetle.
House Longhorn Beetle.
Deathwatch Beetle.
Wood Boring Weevil.
Can you give me a examples of deleterious materials ?
Asbestos
HAC (High Alumina Cement)
Lead
Difference between wet and dry rot ?
Dry rot can penetrate masonry, different humidity, One of the main differences between wet rot and dry rot is that wet rot needs a higher moisture content to grow. Wet rot fungus likes to grow on timber with a high moisture content of around 50% and above while for dry rot to grow it will germinate at a lower timber moisture content of around 20% to 30%.
What indicators would you look out for if you suspect dry rot ?
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.
Dry rot often occurs in areas out of sight.
How would you advise the client on a like for like replacement of a timber floor structure affected by dry rot, talk me through the steps.
Consider the affected area
Remove affected timbers
introduction additional ventilation
rapidly dry out the area
trat area with a pesticide
replaced timber if splicing go 500mm past affected areas
protect joist ends form moisture ingress
Why is dry rot commonly referred to being more problematic than wet rot ?
As it can pass through masonry.
What typical building defects might you expect to see on a 1960s residential property?
Wood wall slabs
snapped headers
Stone defects
sulphate attack in concrete or chimney stack
damp penetration
timber attacks
lead paint
asbestos
shallow foundations to bays - differential movement
Where a property is suffering from subsidence, what type of cracking might you expect to see ?
Vertical, larger at the top than the bottom
When investigating structural cracking to brickwork in residential/low rise property what recognised standards would you refer to assist in classifying the cracking ?
BRE Digest 251 - Assessment of damage in low-rise budlings - This defines the inspection and cracking sizes to reference.
When investigating structural cracking to brickwork caused by adjacent trees what recognised standards would you refer to assist in assessing the risk posed by the trees present?
BRE Digest 298 - Low-rise building foundations - the influence of trees in clay soil
