Building Pathology Flashcards
What are the types of timber decay?`
Rot (occurring due to damp timbers)
Wood boring insects (subsequently occurring due to damp timbers)
What are the Dry Rot Stages and What moisture Content cannot it form?
Its the most serious form of fungal decay in buildings. It can spread through a complete building and destroy the fabric of the property, it can start affecting timber at a moisture content above 20-40%.
Has Four Stages
Stage 1 - Spores - Present everywhere - Dry rot begins its life as tiny spores, these spores remain inactive until they come in contact with timber and enough moisture to make them active. Typically 20 percent moisture content is enough to make the fungus spores start to attack timber.
Stage 2 - Hyphae - A hypha is a long branching structure of a fungus – typically what fungus spores will grow into if left untreated. Dry rot hyphae are identifiable by the white fine stringy strands that become visible both inside and outside the timber. These strands allow the fungus to grow rapidly inside the timber.
Stage 3 - Mycelium The mycelium is the name given to a collection or mass of hyphae. Mycelium’s are the vegetative part of fungi and can spread very far in masonry and behind wall plaster in search of timber to attack, so you should be sure to treat any infected timber quickly. If left untreated for too long mycelium will grow and spread-out into a thick mass, before turning into its fourth and final stage
Stage 4 - Fruiting Body - The fruiting body is the final stage of the Dry Rot fungus’s life cycle. The fruiting body takes on a mushroom like appearance and it produces Dry Rot spores that it emits from the surface to be carried along by air currents out into the air. Fruiting bodies are formed by the fungi when it detects changes in its conditions. The fruiting body is created as an attempt to preserve the lifespan of the fungus by emitting spores to other areas of the property, effectively starting the Dry Rot fungus life cycle all over again.
Tell me about wet rot?
Identification:
Dark brown staining on the timber.
Splitting or longitudinal cracking along the grain of the timber. Cuboidal cracking can occur but not as deep as dry rot.
Fruiting body rarely found though can be a honeycomb or knobbly, thin and olive in colour.
A damp, musty smell. Timber that is damp to touch. Hyphae is thin brown/black thread-like Mycelium rarely occurs. May have turned into shredded weat.
Moisture content of 45%-60% and between temperatures of -30 to 40oC
Wet rot stays to the damp area and does not spread like dry rot.
If the timbers are in reasonable condition they should be left to dry out in accordance with BRE Good Repair 12.
What are the wood boring insects?
They are species, including certain beetles (‘woodworm’), that feed on wood, usually which is damp/moist and may seriously damage building timbers. In the UK, they include:
The common furniture beetle
Death watch beetle
House longhorn beetle
Powder post beetle.
Can be identified based on their flight holes and frass, refer to BRE guide or Hollis Surveying Building’s to identify.
Why do insects attack timber?
Wood-boring insects only establish themselves where dampness exists. Beetle damage in buildings is usually confined to sapwood, although heartwood is vulnerable too if fungus is present. (usually over 18%)
Good preventative maintenance and moisture monitoring can avert dampness and, therefore, ensuing damage caused by wood-borers. However, over-reliance should not be placed on surface readings from electrical moisture meters. False readings may occur, for instance, because of surface deposits or past chemical treatments.
How do you identify wood boring insect attack on timber?
Boreholes - Different sizes/shapes for different infestations
- If active infestations have sharp rather than round edges
- If active the interiors and bore dust (‘frass’) are not dark but the colour of freshly-cut timber.
Where signs of beetle activity are ambiguous, this can be resolved by monitoring for a year. Water-soluble glue is used to cover a group of holes with acid-free tissue paper, through which beetles will punch their way if present. Alternatively, holes can be clogged with wax polish.
What are the types of water ingress/dampness?
Rising Damp
Penetrating Damp
Condensation
What is rising damp?
Water rise’s upwards due to capillary action between the pores of porous building materials such as brickwork.
Natural osmosis also occurs which causes water to move from materials of lower to higher salt concentrations.
The movement of water is therefore dependant on the size and distribution of the pores within the wall and the presence of soluble salts.
What are the effects of rising dampness to a building?
- Rotten skirtings etc.
- Damaged suspended timbers lead to ultimate failure.
- Rot
- Increased vapour levels may pose a risk of condensation.
- External walls may be compromised through this saturation by frost action and efflorescence (salt crystallisation).
Common reasons for the presence of rising damp?
Absence or failure of DPC
The 1875 Public Health Act introduced DPC as mandatory. Therefore property’s prior to then may not have a DPC.
Older houses may have used a slate DPC which may have cracked/failed. Bitumen or lead DPC’s may have flattened/become brittle. Injected DPC’s may have failed due to in-continuous banding.
Bridged DPC’s from raised ground levels externally
Hard exterior surfaces will not allow evaporation of water from the ground and may cause surface water to run back towards the house.
What is Penetrating Damp?
Penetrating damp is caused by water leaking/penetrating a building’s envelope this can be\through walls, roofs, windows, openings or breaches etc.
It tends to happen as a result of failures to a buildings envelope.
The rate of which the dampness occurs will depend on the severity of the conditions such as the internal pore structure of the material, how much will evaporate into the air prior to reaching its internal surface.
Common reasons for the presence of penetrating damp?
- Absence or failures in damp-proof trays in cavity’s
- Direct entry through open joints in construction
- Absence or failure of flashings
- Absence or failure of drip
- Damaged service/plumbing pipes.
- Bridged cavities.
Tell me about condensation
When air becomes saturated at 100% RH, water vapour will condense on cold surfaces creating water droplets which is known as condensation.
Ideal conditions: 50% alongside sufficient heating to minimise saturating the air.
Humidity:
Humidity is the concentration of water vapour in the atmosphere.
Relative humidity is the amount of water vapour present in air expressed as a percentage against the the amount needed for saturation at the same temperature.
Colder air can hold less water vapor than hotter air. Therefore heating the property is critical.
Absolute humidity is termed as the pure amount of water in the atmosphere.
So how does condensation affect buildings?
Mould growth and water vapor condenses on cold surfaces forming droplets.
High levels of vapour are increased from day to day activities such as cooking, washing, bathing etc.
Modern standards such as double glazing, draught proofing will disable some ventilation within the building which will aid condensation.
Human factors including not heating the property will also aid condensation.
What is radon?
Radioactive gasses emitted from the earths surface which can adhere to dust particles and once breathed can cause respiratory issues such as lung cancer.
Usually found most in basements or underfloor voids where the building has been built on areas underlain with granite.
Tell me about corrosion?
Corrosion is a chemical reaction between the environment and a ferrous metal. Direct oxidation of the metal occurs which leads to the formation of Hydrated Iron Oxide which gives the known red layer of rust.
The rust offer some protection but when it flakes off, the metal is exposed more resulting in further corrosion. The oxidation also results in the volumetric expansion of the metal. (wrought iron is capable of expanding 7x)
Direct oxidation:
- Electrochemical reaction that occurs when the metal is in the presence of either:
1. Water
2. Oxygen
3. Electrolyte (Electrically conducting solution, can be iron)
Tell me about Sulphate Attack?
Sulphate salts (typically in calcium, magnesium or sodium) are naturally present in the ground, ground water and various building materials such as hardcore/brickwork etc.
When these salts come in contact with cementitious materials such as renders, mortars, concrete etc under damp conditions, these will react and cause expansion of the cementitious product and cause spalling, cracking, displacement.
Steps can be taken to reduce the likelihood of this through using sulphate resisting Portland cement, DPC’s, Coatings, Minimising contact etc.
Sulphate attack is common within older properties due to the lack of damp proofing and the use of ordinary Portland cement, which is vulnerable to sulphate attack. Also, the use of recycled ashes from burnt fossil fuels / industrial furnaces, as hardcore fill can be very high in sulphate content, causing a reaction with the cement when used beneath the floor slab.
A chemical analysis of soil borings should be undertaken during the design phase of any project involving concrete in contact with the soil to check for the presence of sulphates and determine if they’re aggressive.
What is carbonation, how would you investigate and treat it?
Concrete is naturally alkaline (pH 13) due to the presence of calcium hydroxide, this alkalinity offers a protection to the embedded steel reinforcement from corrosion by acting as a passive layer.
As soon as concrete is poured, it is under attack from pollutants and acidic gasses in the atmosphere (carbon dioxide, sulphur dioxide or sulphur trioxide) enter the pores, cracks or breaches of concrete.
The gasses react with the alkaline material which creates acidic solutions which reduce the alkalinity of the concrete which is known as carbonation. This offers little protection to the steel reinforcement which causes corrosion. Corroded steel can expand up to 7x its volume causing further cracking to the concrete and may lead to structural problems.
Identification: The first time that carbonation is evident is usually when the concrete around the reinforcement spalls and cracks. Over time this will worsen and expose the corroded reinforcement.
Investigation: Carbonation depth is assessed using a solution of phenolphthalein (FEE-NOL-FEE-LANE) indicator that appears pink in contact with alkaline concrete with pH values in excess of 9 and colourless at lower levels of pH. The test is most commonly carried out by spraying the indicator on freshly exposed surfaces.
BRE Digest 444, Part 3 provides guidance on the appropriate repairs:
- Undertake hammer test to establish all loose areas of concrete.
- Hack off loose concrete from around the exposed steel bars.
- Grit blast to remove corrosion and other deposits from the exposed steel reinforcement including hidden faces, to the back of the steel bars, and to intersections of bars.
- Treat the steel re-bar and apply a corrosion inhibitor and bar primer to the surface of the reinforcement.
- Patch repair areas of concrete using a cementitious material and sand, and a polymer dispersion.
- Apply protective anti-carbonation coating.
NOTE: It is possible to undertake Re-Alkalisation to the Concrete by passing an electrical current through the concrete to the reinforcement using an externally applied anode that is attached to the concrete’s surface
Tell me about thermal movement?
Materials will usually respond to thermal movement by:
- When heated expansion occurs (increase in size)
- When cooled contraction occurs (decrease in size)
This is particularly prominent during seasonal change.
When two different materials are bonded together differential thermal movement will occur and the weaker of the two materials will fail.
Tell me about moisture movement in building materials?
Porosity - The absorption of water into porous materials usually increases the volume of the material with a loss of such water resulting in a decrease.
Materials such as mortar will result in a decrease during the drying out as they require more water in their manufacture.
Materials such as soil will expand with moisture and decrease with a loss.
Tell me about efflorescence?
Efflorescence occurs where dissolved salts in porous materials evaporate. During the evaporation process the salts will concentrate to the surface where they will crystallise and form deposits known as efflorescence.
This usually occurs in new brickwork, though in older installations this will indicate a presence of consent saturation.
Tell me about lichen, mosses and algae?
These grow on surface materials which are usually rich in salts.
Play a natural part of the eco system in the decomposition of materials.
The biological growths may cause micro-cracking to some materials such as tiles or stonework and algae can block rainwater goods resulting in other issues.
Tell me about Settlement?
Settlement usually occurs in the early stages of construction work and is usually associated with compression of the soil due to the increased new loads of the soil due to the installation of a building/structure.
Tell me about Subsidence?
Subsidence is the downward movement of the buildings foundation caused by a volumetric change of the soil which may be caused by erosion, mining, change in water level, leaking drains, trees taking too much water causing shrinkage, Clay soils becoming shrinkable.
Cracks usually occur in stepped form and larger at the bottom and smaller at the top. sometimes get horizontal cracking too.
Rectified by underpinning, fixing leaking drains, pruning trees or mass filling to the eroded soil. - MUST RESTORE EQUILIBRIUM IN THR SOIL
Tell me about Heave?
Heave is the volumetric expansion of the soil beneath the building foundation which is usually swelling of the subsoil this can be caused by:
- Cut down/pruned trees
- Damaged drains
- Seasonal action on the ground.
Cracks usually occur in stepped form and smaller at the bottom and larger at the top.
Usually resolved by putting the ground back into equilibrium:
- Fixing leaking drains
- Allowing trees to grow by not pruning as frequently, this will result in them using more water.
Tell me about landslip?
Landslip is the sudden movement of soil.
This could be attained due to a slope or gradual creep or could be the collapse of near mine.
Tell me about failed foundations?
Movement may also occur through the failure of a foundation i.e. heave or subsidence
What are in-direct defects in buildings?
Poor design
Poor workmanship
Change of requirements
Inappropriate alterations
