13 - Building Pathology Flashcards
Building Pathology - Extract from Candidate Guide - Aug 2018 (updated Feb 2022)
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. Settlement often refers to the downward movement of the ground around an excavated space, such as that for tunnels, shafts, or basements.
What is sulfate attack (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. typically in properties between 1945 and 1970.
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 intorudced include the selection of suitable materials, inclusion of a dpm.
What is the Latin for dry rot ?
Serpula lacrymans
What is the Latin for wet rot ?
Coniophora puteana
What is the measurement of the protimeter ?
Prongs = WME - Wood moisture equivalent
Surface reading = Measured to a depth of about 19mm and a measure from 60-999
What may give you false readings from a protimeter ?
Foil backed plasterboard
Can you give me some examples of causes of movement in buildings?
E.g. Subsidence, Heave, Thermal/shrinkage, structural failure
What are the ideal conditions for dry rot to spread ?
Serpula lacrymans requires wood (hardwood or softwood) or other cellulosic materials as a food source. The fungus grows most rapidly on wood that has a moisture content above 30% though not saturated.
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 bioside. If affected structural timber seek guidance from a structural engineer.
Can you expand on BRE 251 ? What are the crack categories ? What are common causes of cracking ?
I have read bre digest 251 assessment of damage in low rise buildings. This defines cracks and assessment of cracking from level 0 a hairline cracking less than 0.1mm up to structural damage cracks greater than 25mm.
Level 0-5 from bRE digest 251. 0 - Hairline crack less than 0.1mm 1 - fine crack - up to 1mm 2 - up to 5mm 3 - 5-15mm 4 - extensive damage - 15-25mm 5 - 25mm+ structural damage
What is subsidence ?
Subsidence occurs when the soil beneath a building is unstable and sinks downward. This is not the same as ‘settlement’, which is caused by the weight of the building, but it can still have a negative impact in terms of the overall structural stability. The opposite effect of subsidence is ‘heave’, where the site upon which the building is situated moves upwards and/or sideways.
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 is rot and how would you identify it ?
- 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.
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.
In 1991 the Span tables were paid for by government and were included within the Building Regulations.
What are the stages of dry rot ?
- Spore
- 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 ?
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.
How do you use a protimeter and what are the limitations ?
Calibrated for timber, used to verify visual inspection cannot be relied upon.
What is a borescope and how do you use it ?
Camera to inspect, normally required to make hole to view into a cavity as an example
What is limecrete ?
Limecrete is a mix of natural hydraulic lime (NHL5) and sharp sand. Sometimes glass fibres are mixed in to give a more durable surface.
What is Alkali Silica Reaction?
Most common alkali-aggregate reaction. Concrete is highly alkaline. Water within the pores will also be alkaline. The water can react with silica in the aggregate which produces a gel which expands and causes the concrete to crack.
It needs silica in the aggregate, moisture and high alkalinity.
Identified by cracking that is bordered by a colourless gel which leads to spalling. Further testing can be carried out to confirm.
Remedies include removing the cause of moisture, remove damaged concrete. Introduce secondary reinforcement if needed.
Can you give me four examples 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.
Can you give me a examples of deleterious materials ?
- Asbestos
- RAAC planks
- Calcium silicate bricks
- HAC (High Alumina Cement)
What is a deleterious material ?
The term ‘deleterious materials’ is a broad one, encompassing not only materials that are dangerous to health or which are the causes of failures in buildings, but increasingly, materials which are environmentally damaging.
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.
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 - probor10
- 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
Explain the different types of cracking you might expect to see on a 2-storey residential property.
Regular Horizontal cracking at regular intervals - wall tie failure
Stepped or diagonal cracking - Movement, location dependant
Horizontal cracking - Differential movement
Cracking larger at top than bottom - Subsidence
0 - Hairline cracks: Less than 0.1 mm in width. No repair action required.
1 - Fine cracks: Up to 1 mm in width. Generally restricted to internal wall finishes. Easily treated using normal decoration.
2 - Cracks easily filled: Up to 5 mm in width. Not necessarily visible externally, but doors and windows may require adjusting to prevent sticking. Can be masked by suitable linings.
3 - Cracks that require opening up: Widths of 5-15 mm. Weather-tightness and service pipes may be affected. External brickwork may need repointing or, in some cases, to be replaced.
4 - Extensive damage: Widths of 15-25 mm. Windows and door frames become distorted, walls lean or bulge noticeably. Requires breaking-out and replacement of wall sections.
5 – Structural damage: Widths greater than 25 mm. Beams lose their bearing, walls require shoring, and the structure is generally unstable. May require major repair works.
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
Give some examples of high-water demand trees.
Elm Oak Willow Poplar Hawthorn - NHBC
What are the limitations of using a borescope to inspect the cavity of a 1960/1970s domestic dwelling?
You can only see a limited inspection, if the cavity has been filled your inspection will be poor
What methods of remedial work are available to deal with cavity wall tie failure?
- Replacement and or removal.
- Replacement via remedial replacement resin set wall ties installed into the brick centre
- Can also sleeve existing wall tie to limit further expansion
- Treat existing wall ties with anti corrosion paint
If a property was suffering from dry rot, what might you expect to see?
- Dependant on the outbreak, a lack of ventilation. You would see damage or cuboidal cracking to the affected timber if visible then
- Spores the dust presence of the rot
- Hyphae 0 fine what strands
- Mycelium - a collection of mass of hyphae
- fruiting body - mushroom like appearance 0 dark red - releases the spores and the cycle starts again
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.
Are there any limitations with the use of a damp meter?
Design and calibrated for timber, foil backed plaster board, black ash mortar will give inaccurate readings, it should be used to back up visual identification
How would you identify condensation in a property?
Consider the location and presence of damp, normally is low air flow/changes area, behind furniture, corners of room, near or adjacent to bathrooms and kitchens. Normally black spots.
Give some examples of the likely causes of penetrating damp.
• Slipped slates
• blocked gutters
• failed tanking systems
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What is nail fatigue ?
That as a roof ages the fixings which are often nails start to fail resulting in tile or slate slippage especially in windy weather conditions.
Explain the cause of concrete carbonation.
The carbon dioxide being absorbed into the concrete to cause calcium carbonate which lowers the concrete ph., which can affect the protective coating on the steel reinforcement.
Explain the testing procedure when testing for concrete carbonation.
- The extent and depth can be confirmed using a phenolphthalein solution. Phenolphthalein solution reacts with the concrete – changes to pink if uncarbonated concrete and remains colourless on carbonated concrete
- Carbonation depth is assessed using a solution of phenolphthalein 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 of concrete broken from the structure or on split cores
- Cover meter can detect reinforcement positions, cover depth and bar diameters
- Structural assessment may be required
What are the symptoms you might expect to find if a concrete floor was suffering from sulphate attack?
- Cracking
- Bulging
- Movement on the walls above or below DPC
- Unevenness to the floor
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
Outline some of the key differences between the characteristics of brown rots and white rots.
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.
Explain what tests could be made to determine is insect attack is live or historic.
- Tell tale sign 1 - Small round exit holes.
- Tell tale sign 2 - fine, powdery dust.
- Tell tale sign 3 - Crumbly edges to boards and joists.
- Tell tale sign 4 - Tunnels within the timber.
- Tell tale sign 5 - Weak or damaged timbers or flooring.
What are the stages of woodworm ?
- Adult
- Eggs
- Lava
- Pupa
Adult
• The cycle begins with the mating of two beetles. Woodworm beetles only have a short lifespan as a mature adult between 10-14 days.
Eggs
• The female beetle will then lay her eggs into the cracks of the timber so that the eggs are protected and don’t become dislodged.
Larva
• After a few days, the eggs then begin to hatch and the new born larva burrow downwards into the timber producing frass – bore dust as they tunnel into the timber. This is the worm stage of an infestation.
• This is the lengthy part of the cycle, as larvae can live from anywhere between two to five years.
• During this time, the larvae will feed its way up and down through the timber (which can lead to structural damage).
• This is also the part of the cycle when woodworm can be detected through the frass being produced. The frass can help us identify the species of woodworm and confirm the woodworm infestation is active.
Pupa
• The woodworm’s lifecycle is almost at an end now. The larvae form a pupal chamber where it ‘pupates’ and changes from the larva into an adult beetle just below the surface of the wood.
• Adult Beetle emerges
• These now adult beetles will eat their way through the timber to create exit holes which can be seen on the surface of the timber. From here the beetles will ‘flee the nest’ and start the whole process again.
• Visit our woodworm page to find out more about these tiny creatures and how we can treat the damage they cause to your home if left untreated.
What is BRE Digest 251 ?
What is BRE Digest 329 ?
What is BRE Digest 401 ?
What are the repair options for cavity wall tie failure ?
Can you give me some examples of high water demand trees ?
- Oak
- Willow
What is Regents street disease ?
Occurs in steel framed buildings with covering masonry or stone. Often found in early 20th century buildings. The porous cladding allows moisture to come into contact with the steel which then corrodes, expands and causing cracking to the facing around the steel frame.
Repairs can include removal of the facework, clean the steel work, apply protective paint. OR Cathodic protection whereby a current is passed through. It does not make good existing corrosion but prevents continuation of process
What is concrete Carbonation ?
- Carbonation occurs when the alkaline elements of the concrete react with carbon dioxide creating calcium carbonate which lowers the PH level of the concrete.
The carbon dioxide can react with the protective coating on the steel and corrode it. Levels of carbonation impacted by compaction, temperature, humidity, carbon dioxide levels.
Overtime the concrete will weaken and crack
It is remedied by removing the delaminated concrete, cleaning the re-bar and patching the concrete.
What is Chloride Attack ?
- Calcium chloride additive was used as an accelerator until it was banned in 1977. The calcium chloride increase the conductivity of the concrete and speed of reaction. Eventually, it will cause the rebar to corrode and expand. Chlorides are also found in poorly washed marine aggregates or being exposed or sea water. The chloride is absorbed into the body of the concrete.
What is Sulphate Attack ?
- Chemical reaction affecting concrete causing it to expand and crack. This is due to penetration of sulphates into the concrete from external sources such as rainwater or the materials mixed in.
- Can lead to large cracks and potential heave.
- Remedy is to break out and replace the concrete.
- Generally occurs in houses built between 45-70’s in areas with mining or close to the sea. Occurs as soon as concrete comes into contact with moisture with sulphate but the cracks vary in the time they show up, depends on factors such as slab thickness, moisture content etc.
What concrete tests can be carried out ?
- BRE444
- Hammer testing
- Visual inspection
- Magnet cover testing
- Phenolphthalein test
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 methods are you familiar with to assess flat roof defects ?
Firstly, visually inspect the roof for any defects and then use a thermographic camera to identify colder areas that may identify areas of leaks.
What should you consider when deciding whether to repair or replace a flat roof ?
The extent of the defect, when the existing roof was recovered, the approximate life span, the cost, timing, clients intentions for the building
What are the possible causes of sagging roof ridges and possible secondary problems ?
Decay to the timber forming the structure, inadequate supports or alterations carried out to the structure. Change of roof coverings. Secondary problems may be slipped tiles or opening joints at the ridge allowing water ingress.
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.
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.
- 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.
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.
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.
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.
What is damp ?
A building is considered damp if moisture becomes visible through discoloration of finishes or causes mould growth, sulphate attack, frost damage or puddles and drips.
How can you test for damp ?
Speedy carbide meter or protimeter.
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 three remedies for rising damp ?
It is caused by a lack/failure of DPC or bridging. The remedies can be injecting DPC, removing the cause of bridging which may involve reducing the ground level.
How would you identify penetrating damp? What are the causes? How would you remedy it ?
Identify what the building is exposed to. Is there a leak, overflowing gutter etc. Identified by discolouration or damp patches which can darken and grow if left for long time. Remedies can be unblocking a gutter, fixing roof tiles, flashing, faulty pointing, lack of dpc below the parapet.
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.
How would you tell the difference between rising damp and condensation with a moisture meter ?
Rising damp generally only occurs to the bottom 1m of the wall. Test the moisture in the wall at 300mm intervals. If it is closer to the ceiling, odds are that it is condensation particularly if there is a mildew on the surface.
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.
When was DPC made compulsory ?
1875
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
- Up to 2mm – very slight/aesthetic
- 2-5mm – slight / aesthetic
- 5-15mm – moderate/ serviceable
- 15-20mm – severe/ serviceable
- Over 25mm – very severe / stability issues”
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 types of soil is susceptible to heave and what are the possible causes ?
Cohesive soils such as clay. Could be because of trees or high water table, leaking drains etc.
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 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
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
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.
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.
Name the three types of asbestos and examples of where they are found.
- Chrysolite – most common asbestos in buildings. Corrugated asbestos cement sheets.
- Amosite – found in fire retardant materials
- Crocidolite – pipe insulation, plastics, cement products.
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
What are the stages of plastisol degradation ?
Loss in colour, caulking and delamination
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/elastomeric coating. 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 is Japanese knotweed ?
Herbaceous perennial plant.
What does Japanese knotweed look like ?
Hallow stems with raised nodes. Similar appearance to bamboo. Can reach 3-4m per year. Broad leaves with small white flowers
Why is Japanese Knotweed and issue ?
Invasive species which forms thick colonies that crowd and kill over species. Extend 7m horizontally and 3m deep making excavations difficult. Plant is resilient to normal weed killers and cutting. Needs herbicide application to kill it over a period of months.
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.
How should it be dealt with ?
Injected with herbicide or excavated with the roots and disposed.
What are common causes of stone deterioration and what remedial measures would you suggest ?
- Inherent characteristics – some stones have layers with different erosion rates. Small cracks in the stone can cause problems.
- Salt crystallisation – salts in solutions pass into the stonework. As the stone dries, the salt crystallises which expands and blows the stone. Damage usually shows ass a powder on surface but can split the stone.
- Frost Attack – General freeze thaw particularly if the stone has large pores.
- Incorrect bedding – Stones should be laid in natural bedding position as it is stronger like this. If laid vertically, the layers are vertical making them more vulnerable to damage.
- Incorrect pointing – inappropriate mortar mixes can cause issues with the mortar and stone. If it is too strong, the mortar will crack with movement or shrinkage which may allow water penetration. Strong mortar may also prevent moisture evaporating out and will instead go through the stone and potentially cause salt crystallisation.
- Expansion of Metal – Iron and steel cramps have been used as fixings for stone. When they rust, they expand and can fracture the stone
What typical defects are found in 60’s/70’s commercial buildings ?
- Asbestos
- Concrete defects
- Cold roof
- Wood wool slabs
What typical defects are associated with Victorian terraced houses ?
- Failed on lack of DPC
- Insufficient foundations
- Poor ventilation to floor voids
- Damp penetration
- Lead pipework.
