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 (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 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?
.g. Subsidence, Heave, Thermal/shrinkage, structural failure
What are the ideal conditions for dry rot to spread ?
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. Its 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 a 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 ?
Wet Rot:
Color Change: The wood often darkens to a brown or black color.
Cracking: Cracks may appear on the surface, typically along the grain of the wood.
Soft and Spongy Texture: The wood feels soft, spongy, and can be easily damaged.
Shrinking: The affected wood may shrink and become deformed.
Fungal Growth: You might see fungal growth on the surface, which can appear as a black or brown mass.
Dry Rot:
Color Change: The wood may become lighter in color, turning a dry, brittle brown.
Deep Cracks: Deep longitudinal cracks along the grain of the wood.
Mycelium Growth: A white or grey cotton wool-like growth (mycelium) on or near the wood. In advanced stages, you might see a fruiting body (a mushroom-like structure) which is rust-colored.
Red Dust: Rust-colored spore dust around the affected area.
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
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
-Flight holes random orientation, mainly in direction of grain.
- Softwood, European hardwoods
LONG HORN BEETLE
- Flight holes, few large oval, 6-10mm largest dimension.
- Sapwood or softwoods particularly roof timbers.
DEATHWATCH
- Flight holes circular 3mm diameter
- Mostly oak and elm (hardwoods)
WEEVIL
-Flight holes, small ragged, 1mm diameter.
Decayed softwood and hardwoods in damp conditions.
Can you give me a examples of deleterious materials ?
Asbestos
RAAC planks
Calcium silicate bricks
HAC (High Alumina Cement)
why is (High Alumina Cement) considered delterious ?
High Alumina Cement is considered deleterious primarily due to the conversion process, which leads to a loss of strength and increased porosity over time. This makes HAC less suitable for long-term structural applications unless the specific conditions that necessitate its use are carefully managed. Regulatory changes and historical failures have also contributed to its cautious use in the construction industry. Proper understanding and application are crucial to mitigate the risks associated with HAC.
why is calcium silicate bricks considered deleterious ?
Calcium silicate bricks are prone to thermal movement due to their high thermal expansion coefficient, moisture content, bonding and joint issues, and environmental factors such as temperature fluctuations and exposure to sunlight. These factors can lead to cracking, joint failure, and overall structural issues if not properly managed. Proper design and construction practices, including the use of compatible mortars and the inclusion of expansion joints, are essential to mitigate these effects.
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.
Why is dry rot commonly referred to being more problematic than wet rot ?
Ait 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.
Refer to BRE digest 251
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 - Assessing cracks in houses. 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
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.
Concrete carbonation is a chemical process in which carbon dioxide (CO₂) from the air reacts with calcium hydroxide (Ca(OH)₂) in the concrete to form calcium carbonate (CaCO₃), reducing the concrete’s alkalinity. The lowered pH can lead to corrosion of the steel reinforcement within the concrete, as the protective oxide layer on the steel is compromised.
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 is BRE Digest 251 ?
Assessment of damage in low-rise buildings
What is BRE Digest 329 ?
Installing wall tie in existing construction
What is BRE Digest 401 ?
Replacing wall ties
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
How is concrete Carbonation remedied ?
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 (Tests compressive strength )
Visual inspection
Magnet cover testing (detects the steel )
Phenolphthalein test (High PH =Pink, low PH = no colour change - carbonated concrete)
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.
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. Significant roof repairs will trigger the need to comply with regulations - 50% rule.
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 masonary through adding masonary dust into a container with calcium carbide which releases a gas in proportion to the moisture present.
What are 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.
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
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
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 - white - most common asbestos in buildings, Corrugated asbestos cement sheets.
Amosite - brown - found in fire retardant materials
Crocidolite - blue - pipe insulation, plastics and 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 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 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
What kind of defects did you find in industrial buildings ?
- Cut edge corrosion
- plastisol degradation
- Asbestos use in insulation
What are the causes of staining to chimney breasts and the remedial work required ?
- Sulphate attack
- defective flashing
- removal of stack below
What are the likely causes of a leaning chimney breasts and what are the remedial works ?
Erosion, acid attack, salt crystallisation could all cause the stack to lean. BRE good repair guide states any lean of the stack of more than 1 in 100mm is unsafe. Consider lining the flue with a liner and replace broken bricks and pots. Relaunch the top if needed. Worst case scenario rebuild the stack.
Name some typical defects of a Georgian building (1700’s) ?
Water paths through parapets, hidden valleys and gutters
Springy floors resulting from decaying timber floor joists. mainly caused by poor cross-ventilation. heel drop test to test the springy floor.
Rotten or stuck sash windows
Blocked internal gutters.
Damp penetration in solid walls
Corroded cast iron railings bursting stonework
Bowed brick walls, caused by the practice of lightly bonding high-quality facing bricks in with poorer quality bricks of the main wall, unbonded party walls and front walls and decaying coursed timbers buried in walls
Failure in roof trusses caused when roof ties rot and begin to spread. Dislodged joists and ridges caused by bomb blast damage.
Leaning chimneys/over-tall stacks/damp penetration via stacks
Perforated lead work or splitting caused by over-beating or poor maintenance
Missing or badly altered load-bearing timber partitions
Damp basements
Failure of timber lintels
Poorly applied or painted stucco limiting water evaporation from walls
Downpipes decanting on to lower roofs from roofs above, causing temporary flooding in heavy rainfall
Name some typical defects of a Victorian 1800’s (1837 – 1901) ?
Blocked air vents to ground floors, causing dry rot
Failed or lack of damp proof course – rising dampness, penetrating damp, efflorescence on plaster, decay to skirtings
Delamination of brick skins – bulging of brickwork
Over notching of floor joists for retrofit of services – deflection of floors, reduction in load bearing capacity
Poorly fitting sash windows, risk of decay within window reveals, water penetration beneath sub-sills, draughty or dangerous operation, decay in concealed areas, lack of security
Roof covered with concrete interlocking tiles – overloading of roof structure, bowing of rafters and purlins, roof spread
Settlement of bay windows – internal cosmetic damage, distortion in load-bearing elements
Wall tie failure (particularly in black ash mortar)
Heave or subsidence of shallow foundations
Nail sickness – ferrous nails corroded
Name some typical defects of a Edwardian 1900 – 1920’s ?
Blocked air vents to ground floors, causing dry rot
* Failed or lack of damp proof course – rising dampness, penetrating damp, efflorescence on plaster, decay to skirtings
* Delamination of brick skins – bulging of brickwork
* Over notching of floor joists for retrofit of services – deflection of floors, reduction in load bearing capacity
* Poorly fitting sash windows, risk of decay within window reveals, water penetration beneath sub-sills, draughty or dangerous operation, decay in concealed areas, lack of security
* Roof covered with concrete interlocking tiles – overloading of roof structure, bowing of rafters and purlins, roof spread
* Settlement of bay windows – internal cosmetic damage, distortion in load-bearing elements
* Wall tie failure (particularly in black ash mortar)
* Heave or subsidence of shallow foundations
* Nail sickness – ferrous nails corroded
How would you identify concrete carbonation ?
Occurs to reinforced concrete buildings and structures – it is inevitable
Fine cracks appear in the concrete causing the reinforcement to corrode
Hairline cracks appear along the reinforcement line
The reinforcement expands due to the rusting
Concrete spalls and cracks exposing the reinforcement
What are the remedial measures for concrete carbonation ?
Replacement – this involves removing defective concrete and cutting out the reinforcement to damaged members. New reinforcement is fixed but welding to existing and new concrete is cast. This is the simplest method and completed by specialist contractors.
Gunting – a propriety process in which fine concrete is sprayed onto a concrete surface under repair of high velocity.
Coating – coatings, sealants and membranes can be effective in reducing the carbonation process. however, if chloride is present at rebar depth then the coating will not prevent carbonation.
Electrochemical re-alkalisation – the cathodic reaction around rebars produce hydroxyl ions. The steel cathodes also attack alkali metal ions towards its surface, so high alkalinity is restored around rebar. A temporary anode (steel mesh) is attached to concrete, the electrolyte penetrates the concrete and raises the alkalinity at the cover. An anti-carbonation coating is applied.
Cathodic protection – this is a permanent and very expensive technique. an anode system (coating or mesh) are sprayed or fixed to the whole surface of concrete. A current is applied which passes to the reinforcement, which is then made cathode preventing corrosion of the reinforcement.
What is HAC High alumina cement ?
High Alumina Cement was used in the production of pre-cast concrete sections. This has very high strength at an early stage, however, loses strength as it ages and is susceptible to chemical attack in damp conditions.
Introduced in 1925, cement producer Lafarge commenced the UK manufacture of High Alumina Cement to provide concrete that would resist chemical attack, particularly for marine applications.Used in the UK from 1950-1976 in the manufacture of pre-stressed concrete beams
What are the problems with HAC ?
HAC concrete undergoes a mineralogical change known as conversion. During this process the concrete increases in porosity which in turn results in a loss of strength and reduction in resistance to chemical attack. The higher the temperature during the casting of the concrete the more quickly conversion takes place.
Remedial measures for HAC ?
An investigation should be undertaken consisting:
Sample testing
Collect details of construction materials used – the local authorities hold records of HAC buildings
If the strength has been reduced – reduce the live loads or strengthen
In the case of reinforcement corrosion – localised repairs can slow further deterioration
What is sulphate attack ?
Sulphate attack can cause serious damage to brickwork and concrete by creating expansive force that are, or can be, sufficient to disrupt mortar and create significant expansion, bowing and cracking of concrete floor slabs together with related collateral damage.
In some subsoil there can be a problem with sulphate attack. It occurs when the fill material (hardcore) beneath the slab contains sulphates and these migrate into the concrete. The sulphates react with the concrete causing it to expand.
Calcium, magnesium and sodium sulphates occur naturally in some clays and other sub soils
The sulphates dissolve in the groundwater and permeate the concrete.
This leads to an aggressive chemical reaction between the sulphates in solution and one of the chemicals in the cement.
The resulting compound expands rapidly as it forms and this can crack the foundation concrete.
If sulphate attack is a possibility it is wise to use sulphate resisting cement.
what happens to clay soil vs sand when it get gets wet?
clay expands = heave like., sand washes away
dentification of sulphate attack ?
symptoms and tests for Concrete Carbonation, Sulphate Attack, Alkali-Silica Reaction (ASR)
Concrete Carbonation
Symptoms:
Color change (phenolphthalein test)
Surface dusting
Fine cracking
Corrosion of reinforcement (rust staining, spalling)
Tests:
Phenolphthalein test
Depth of carbonation measurement
Sulphate Attack
Symptoms:
Expasion and cracking (map cracking)
Surface scaling
Loss of strength
White efflorescence
Tests:
Visual inspection
Chemical analysis (XRD, SEM)
Core sampling and testing
Alkali-Silica Reaction (ASR)
Symptoms:
Network cracking
Gel exudation
Discoloration
Expansion
Tests:
Petrographic analysis
Chemical tests (SEM-EDS)
Expansion testing (concrete prisms, mortar bars)
Causes of sulphate attack ?
Must be a high level of water-soluble sulphates within the adjacent ground. To affect concrete buried in the ground, the concrete must be of low density and there must be a large amount of moisture movement through the concrete. Common cause is contaminated hardcore beneath the concrete floor slab. The sulphates become mobile due to a broken drain or high-water table.
The process of sulphate attack is:
* sulphate enters concrete (solution form)
* water evaporates leaving the sulphates
* sulphates react with calcium hydroxide and calcium aluminates causing expansion
* the concrete deteriorates causing cracking and heave
What is Sulphate attack testing ?
BS 1881-124:2015 provides method of testing concrete samples
Assuming that concrete contains 15% by mass of cement, sulphate content can be expressed as a percentage of the mass of cement with anything over 5% likely to be harmful. In severe cases, 10-15% has been identified.
Visual indicators of affected concrete may be the existence of a flaky or crumbly concrete and in the case of thaumasite, a white mush.
Remedial measures for sulphate attack ?
Remove affected concrete and start again with DPM
Remediate the ground
Investigate sulphate levels
What are the symptoms of ASR reaction ?
Occurs where the chemical within the cement react with silica forms a gel substance which absorbs water and expands creating cracks where water can enter. Further cracking may occur as a result of water freezing within the cracks.
* Cracking
* Small pop outs
* Map cracking
* Tensile strength reduced
* Gel absorbs water causing further cracking
* Cracks run parallel to reinforcement bars
What is Chloride attack ? (salts)
Chlorides may either ingress (from penetration of de-icing salts) or cast insitu as sea dredged aggregates or calcium chloride additive.
Chloride ions attack the reinforcement can cause:
In certain circumstances ‘pitting’ corrosion can occur – when the steel is effectively eaten away without the formation of expansive rust
Corrosion of steel reinforcement is localised compared to carbonation and much more rapid.
Spalling of concrete
Significant loss of cross-sectional area
Pit in bar surface – rebars could be completely eaten away
Visual sign of cracking and spalling following expansive rusting
Tests for chloride attack ?
Removal of cores for analysis in the lab
Petrographic analysis
Drilling dust, disregard 5mm
Profile grinder to remove dust
Remedial measured for chloride attack ?
Cathodic protection
Corrosion inhibitors
Epoxy resin repairs
What is rising damp ?
Upward movement of moisture through permeable building materials such as brick by capillary action. It rises up the wall often to a height no more than 1.5m and usually leaves a characteristic horizontal tide mark.
What are the symptoms of rising damp ?
Damp patches
Peeling and blistering of wall finishes
Tide mark up to 1.5m above floor level
Sulphate action
Corrosion of edge beads
Musty smell
Condensation / mould growth
Rotting timbers – skirting boards, frames, linings and doors
Hydroscopic salts (nitrates and chlorides from ground water) absorb moisture which can be dissolved and moved to the surface of a material and cause extensive staining and disruption of finishes.
What are the causes of rising damp ?
Failure of DPC
DPC bridged – raised external soil levels or pathways of rubbish / debris
Mortar droppings within cavity
DPC not laid correctly – lap minimum 150mm
If suspended timber floor has been replaced by a solid floor, check for a difference in level of DPC’s
Rain penetration
Leaking gutters
Plumbing defect
Persistent spillages
Water trapped in building fabric
Remedial measures for rising damp ?
Resolve all water ingress – gutter, leaks etc.
* Let the building dry naturally – promote ventilation
* Hack-off and remove affected plaster area internally
* Re-plaster (using renovation plaster) and redecorate. Renovation plaster stops salts and controls damp passing through the walls
* Ensure all timbers are replaced as required
* If the DPC is damaged – renew
How would you know if your guttering is too small for the property?
Refer to approved document H section one and look at table 1 = for the calculation of drained area and then table 2 = Gutter sizes and outlet sizes
What is penetrating damp ?
Penetrating damp (or moisture ingress horizontally through the wall fabric) is an issue that can affect all buildings. Defined as roughly circular area on internal fabrics.
Remediation for penetrating damp ?
Fix the specific issue relating to the water ingress
What is condensation ?
Moisture in the air (water vapour) is held in high temperature air and when it comes into contact with a cold surface it is cooled, and excess vapour condenses (dew point).
What is interstitial condensation ?
It is condensation within the structural elements.
It has less immediate impact on the occupation as it occurs within or between the layers of the building envelope, where the dew point exists at depth within a building element, component or material.
Building at risk from interstitial condensation:
Structural components liable to rot e.g. timber framed walls of timber deck cold flat roof
Structural components liable to corrode e.g. steel framed walls
Impermeable out layers e.g. walls with impermeable cladding
Metal reinforcements e.g. reinforced concrete framed buildings
Buildings likely to have high internal vapour pressures e.g. swimming pools or textile factories
What is the life cycle of damp ?
Spore
Hyphae
Mycelium
Fruiting Body
What is required for rot to continue ?
The fungi will only survive and thrive in certain conditions:
* FOOD (TIMBER) - Sapwood is attacked as it contains nutrients
* MOISTURE - moisture must be present for decay to occur and moisture content of timber is key
* TEMPERATURE - Fungi growth can be killed off by low or high temperatures
* AIR - Fungi require oxygen, if air is excluded, decay will not occu
What is the Dry Rot Definition ?
Fungal timber decay occurring in poorly ventilated conditions in buildings, resulting in the timbers becoming dry and crumbly. There are typical symptoms of dry rot which are cuboidal cracking, hyphae, mycelium and fruiting body.
What are the causes of dry rot ?
These conditions are usually found where water is coming into contact with the timber directly.
The most common defects allowing water entry are:
Failure of roof covering or rainwater goods
Defective rendering
Inadequate ventilation
Defective DPC
Plumbing leaks
Remedial measures for dry rot ?
Detailed and extensive survey should be undertaken to identify the areas of timber and masonry affected.
If structural timbers have been damaged it may be necessary to get a structural engineer to assess
Determine the full extent of outbreak:
Cut out decayed timber to 0.5m beyond decayed wood, remove and burn.
Hack off plaster / rendering and remove skirting, architraves and other joinery from area to be treated to 2m beyond.
Remove surface mycelium from exposed masonry and wire brush.
Surface application of fungicidal fluid - water based surface biocide by brush or coarse spray.
Fungicidal rendering - fungicidal barrier to a greater depth
Preservative plug / paste inserted in holes
Irrigation - large quantities of water based fungicidal solution. Only to localised areas.
Treat sound, damp timber with organic preservative - preservative to sloping holes drilled into the wood or pressure injection OR proprietary paste treatment
Use preservative treated replacement timbers: pressure impregnated or organic solvent type of preservative.
How do you identify subsidence ?
identified by diagonal cracking which is usually tapered (of uneven width ) in the buildings structure/ façade and verified by leaning or pulling of the building. Subsidence usually shows up as cracks that are typically wider at the top than the bottom . They commonly appear around windows, doors and other weaker areas. Doors and windows may stick when opening them, walls and floors may show signs of distortion.
What are the causes of subsidence ?
Usually localised to certain areas of foundation- not distributed across the whole foundation
Therefore ground movement within these area will cause rotational movement on the foundation, which generates rotational forces within the building structure
Common in building built up clay
If the soil becomes dry due to water being sucked out by trees or a drought, the clay contracts and pulls the foundation causing deflection and structural damage.
It can occur when excess water leaks into the soil with high sand / gravel content and washes soil away from foundation, may be due to a leaking drain.
It can be a consequence of mining where the effect can be sudden, the extent of this depends on the method used for mining i.e. dredging, mining or pumping
Remedial works for subsidence ?
Refer to BRE Gidence Subsidence damage to domestic buildings.
Remedying the source of the problem can be effective, however it can sometimes make things worse i.e. removing a tree causes moisture to return = heave
Underpinning is an option but it is expensive and disruptive
Use pneumatic jacks to lift the building and reverse the movement
What is settlement ?
Downward movement of the ground or any structure on it, due to soil consolidation as a result of the load applied by the structure of the building.
How do you identify settlement ?
Cracks occur at the junction between new elements
- Differential movement between two elements
What are the causes of settlement ?
Occurs due to the pressure applied to the subsoil by a new building
Water contained within the sub soil squeezed out by new load
Amount of settlement depends on soil type
What is heave ?
Expansion of the soil due to climatic and other factors (e.g., frost or removal of trees). The mass upwards movement of material as a result of expansion.
How do you identify heave ?
Expansion of the corner of the building causing lifting.
Can be measured on a site over a period of time.
Check shrinkage potential of clay soil using industry data
What are the causes of heave ?
The felling of trees in the vicinity of existing buildings stops the removal of moisture from the soil and the soil soaks up the water that the tree would have removed. Heave generally occurs in clay soils
What are the remedial works for heave ?
In the event that removing a tree is unavoidable, it is advised pollarding be carried out to slowly reduce the trees capacity to remove water from soil. Potentially necessary to seek advice from a geotechnical engineer
What is cold bridging ?
It is a weak spot in the insulation surrounding a house. Cold bridged (also known as thermal bridges ) occur whenever there is a break in the continuity, or a penetration of the insulation.
Common areas for cold bridging ?
Roof and wall abutment
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
Do you have some examples of deleterious materials ?
Asbestos, brick slips, Raac, lead paint, wood wool, horse hair plaster, silica dust , Polyurethane foam, high alumina cement
What is a cavity wall tie ?
Cavity wall ties were introduced around 1920’s where external walls were changed from solid 225mm thick to cavity walls. Wall ties have undergone change from ferrous metal through to zinc coated, bituminised, galvanised plastic and ceramic to stainless steel. It is used to connect the two skins of the cavity wall together.
How do you identify wall tie failure ?
- horizontal cracks in bed joints of brickwork every 6- 8 courses (usually external ) long with some diagonal cracking
- Damp patches internally where there may be cold bridging in the tie position
- Walls leaning or bulging (typically gable walls )
- Upward movement can result in an upturning of the roof, particular at the gable end to alleviate pressure following expansion of wall ties due to corrosion, known as the pagoda effect
- internal wall cracking and lifting of walls and roof structured in extreme cases
- Increasing problem with cavity wall ties made from stainless steel. It arises when the galvanising is not of sufficient quality and the outer leaf of the cavity walls allows penetration, usually due to porous brick/blockwork. If ties rust the swelling effect may cause horizontal external cracks to appear in the wall.
What are the causes of wall tie failure ?
Age of ties, poor quality of coatings
Insufficient wall ties
Badly fitted ties, upside down or not 50mm embedment in the leaf
Poor quality mortar
Sea dredged aggregate in mortar
Corrosion due to failure in joints
What are the remedial action for wall tie failure ?
Replace existing wall ties with new stainless steel wall ties, min. 3per sqm
Additional remedial wall ties at vertical centres to jamb openings and at roof and corners
Remove or isolate existing defective ties
Clean cavity debris
What is a woodwool slab ?
Used as a permanent shuttering. Formwork is used to contain concrete in order to mould it to the required dims and to support it until it can support itself. It may be left in place for the lifetime of the building.
What are the defects linked to woodwool slabs ?
Concrete does not adequately get compacted.
Risk of poor cover to the steel and hence loss of durability, possible reduction in strength, and loss of fire resistance.
Voiding and honey combing due to vibrations. Poor bond or failed bond between the wood wool and the hardened concrete.
Buildings constructed from 1950 to the mid-1970s are most likely to be affected by this form of construction.
If permanent shuttering is discovered, intrusive investigations may be needed to determine the adequacy of concrete cover to the steel reinforcement. If voiding is present, the affected area can be exposed and repaired using hand-fixed concrete repair methods or, if over a larger area, sprayed concrete.
What is cut edge corrosion ?
Steel edge sheets are exposed to oxygen which are prone to corrosion which is exacerbated by water and pollutants. Consequently, the factory coating can peel off from these edges causing them to corrode. Tough cut edge corrosion usually begins around edges it gathers speed through capillary water action and can spread.
What are the remedial measures for cut edge corrosion ?
Area must be first cleaned and prepared for treatment.
Depending on the severity of the corrosion, loose paint, rust and corroded areas are often removed manually, to which a high-quality weatherproof sealant is then applied to the effective areas.
Painting the cut edges and periodic re-painting where access is possible may provide a solution. If sheets with corroded edges are not repaired or replaced, further damage to the sheet may result, with increased risk of water penetration. Delamination of decorative coating may also be associated with cut-edge corrosion.
What clues were present to lead you to suspect the presence of dry rot ?
The presence of mycelium, fruiting body and the damage to the timber suspended floor.
Outline the key differences between the characteristics of brown rots and white rots.
A
Brown rots cause the wood to become darker in colour and to crack along and across the grain ;when dry, very decayed wood will crumble to dust. Many common wet rots are brown rots; dry rot is also in this group.
White rots cause the wood to become lighter in colour and lint-like in texture, without cross cracks.All white rots are wet rots. wet rot green fruiting body.
What is your opinion of the use of chemicals used to treat timber and brickwork when eradicating dry rot ?
Can be used however the source of moisture should be eradicated and the drying out and rapid heating of the space should be encouraged
What do you understand by the term environmental control in respect of treating dry rot ?
Using the weather, wind, etc to assist in removing the moisture and the conditions that are not suitable for rot.
How did you determine the amount of opening-up required when inspecting rot ?
Via an initial inspection from removing a floor boards to confirm extents
What is wall tie failure ?
Wall tie failure can happen where there has been corrosion of the existing wall ties or when insufficient or incorrect wall ties have been installed. When a mild steel or galvanised steel wall tie corrodes, there is a build up of rust (also known as iron oxide), which causes the tie to expand in size.
You say the property was 1900’s what kind of wall tie were present?
I would expect wall ties to be steel fish tail wall tie.
Cavity were widespread introduced 1920
What other materials were used for wall ties ?
Steel and Iron, now made of stainless steel to reduce the chance of corrosion.
What defects might you find within the roof space?
Interstitial condensation
Wood boring insect attack
Roof spread
Water ingress
Can you name some concrete defects ?
Concrete Carbonation
HAC
Alkali Silica Reaction
Chloride Attack
Sulphate Attack
If you identified movement in a building, what further investigations might you wish to undertake?
Consider the location
Recent works
Construction of the building
Type of the cracking
Opening up works
Further investigations
Explain how you could use thermal imaging to identify heat loss in a building ?
Thermography uses specially designed infrared video or still cameras to make images (called thermograms) that show surface heat variations. Energy assessors use thermography as a tool to help detect heat losses and air leakage in building envelopes.
What other type of building defect can thermal imaging be used to identify ?
Water ingress
How far past affected timber should you splice?
500mm
What is RAAC?
Reinforced Autoclaved Aerated Concrete is a lightweight form of concrete used in roof, floor, cladding and wall construction in the UK from the mid-1950s to the mid-1980. They have a strict lifespan and can fail dramatically without warning.
What are the components of rot?
Moisture, food, fungi
How would you treat dry rot in plaster?
Cut back 1000mm from affected area
What are the limitations of crack classification?
They are simplified - does not consider if it is active or historic movement.
What tools would you use to measure a crack?
Initially a steel ruler, then either a tell tale or screws and callipers.
If it was internal I would use a magnified graticule.
In a hard to access location I would use a displacement transducer.
What conditions of the concrete make it vulnerable to ASR?
Pourous
Silica containing
Shallow rebar
What is concrete cancer?
Its a general term to describe the corrosion of rebar that often leads to the cracking of concrete
What is the types of roof load?
Dead load (constant load, e.g. building itself)
Live load (not constant, e.g. snow/rain, occupants)
Transient load (sudden changes e.g. wind)
What is formaldehyde?
A type of resin/chemical used in construction materials that has to be monitored as it is carcinogenic.
What is radon?
A type of natural gas which in high quantities and consumed in enclosed spaces is carcinogenic
What are some potential causes of damp and mould spores in a residential property, and how can you use visual observations and equipment like pole cameras to identify the underlying issue?
Where there is a source of moisture
Defective roof coverings
Thermal bridging
Interstitial condensation (‘between layers of construction’)
What is BRE 251, and how does it help you classify and assess structural damage like the stepped cracking to the rear of the property?
It helps you identify the implications, such as aestetic, serviceability (e.g moisture ingress) and structural
What typically causes mould?
Thermal bridging or water ingress
Why is mould a concern?
They produce toxins which can be harmful to health
What does mould require?
Mould requires four factors for growth:
Mould spores - always free floating
Food - anything that contains carbon
Appropriate temperature - very wide
Moisture - 70% humidity
What goes in concrete mix?
cement, sand, stone, and water
1 : 2: 3
How do you identify and treat chloride attack?
Identified by noting rust staining and delamination of concrete. Examining the rebar will show localised breakdown where there is pitting.
Can carry out localised repairs however, if the chlorides are in the body of the concrete, it will continue to deteriorate. Better solution which costs more is cathodic protection where an external anode is connected to the metal and the passage of the current stops corrosion.
What is pitting?
Eroded holes, typically in concrete
What is cathodic protection?
protection of a metal structure from corrosion from water by making it act as a cathode (negatively charged)
What size (drop) should a cavity tray be?
Min 150mm size.
What do you need when installing a cavity tray?
Weep holes
What would you do if you couldnt install a cavity tray?
Specify a protection cream like stormdry
Where should cavity trays be installed?
DPC level*
Openings and penetrations
Roof/wall junctions
Intermediate levels
What should you consider if installing the cavity tray at DPC level?
The cavity below the DPC should be filled with concrete up to a level of 225 mm below it. Failing to add concrete properly can make the blockwork collapse inward. After filling the cavity with concrete, you can add a cavity tray to the wall.
What materials are cavity trays made of?
Lead
Rigid plastic
Bitumen
Where would you find advice regarding what cavity wall tie to use?
Part A Building Regulations: Structure. Table 5
Can you give me some examples regarding cavity width and length of wall tie?
50mm to 75mm = 200mm tie
76mm to 100mm = 225mm tie
101mm to 125mm = 250mm tie
Typically you take the nominal length, add 125mm and select the nearest stock length
How much bearing should a cavity wall tie have?
50mm
What are the types of cavity wall tie?
Type A - heavy duty
Type B - general purpose
Type C - basic duty
Type D - light duty
Above to BS 6697
Selected on the basis of design loading and cavity width.
What is the purpose of a wall tie?
o prohibit vertical and horizontal planes from moving
Why wouldn’t you expect to see a heli-tie in a base build?
Its helical shape is designed for installing into existing structures. There are more heavy duty and affordable alternatives for use in a base build.
What wall tie would you have expected to see in the base build?
Type 1 as it can be used in any building of any size
How many wall ties do you need in masonry?
2.5 per m2. 900mm (H) x 450mm (V) centres. Evenly distributed and around openings (V=225mm).
If fixing masonry to timber, what should you consider?
Due to increased expansion action seasonally in timber, more wall ties should be used. 4.4 pm2 for wind speeds up to 25m/s (90km/h), increase centres if wind loading is to be more severe.
What should wall ties be made of?
Non-ferrous= iron. Steel is an iron alloy.
What types of brick are there?
Burnt clay brick
Engineering brick
Concrete brick
Sand lime brick
When would you use lime mortar or cement mortar?
Lime mortar is more gentle and is more flexible once cured. It also intrinsically has better waterproofing. It is therefore more sympathetic to softer masonry like sandstone.
Cement mortar is stronger and may be used on more indsustrial high rise buildings or brick slips.
What is the ratio for cement mortar?
1:3 cement sand. More sand = weaker. Ratio of water depends on volume but for 1kg you would want 0.4 parts water.
What is the typical build up of a metal profile roof?
External metal sheet, fixed to a support rail, insulation embedded within spacer framework, VCL, deck or purlin
What is the difference between a cesspit and a septic tank?
A cesspit does not have an outlet and is required to be drained periodically eg once a month
What is a masonry support system?
It is designed to support external masonry façades above openings and at horizontal movement joints. They are generally fixed to concrete or steel frames and adjustment is provided in every direction to allow for tolerance in the structural frame.
What is the difference between engineering bricks and normal clay bricks.
The recesses allow mortar to seep through for extra binding capabilities. They also have a higher compressive strength as well as are less water absorbing
How would you know if there are sufficient movement joints?
BS EN1996 design of masonry structures. This recommends a maximum of 12m of spacing.
What is the difference between a construction joint and a contraction joint?
A contraction joint is formed, sawed, or tooled groove in a concrete structure to create a weakened plane to regulate the location of cracking resulting from the dimensional change of different parts of the structure.
A construction joint is naturally formed when old concrete is poured next to new concrete
What is the purpose of the dpm when pouring concrete?
protect the underside of the slab from attack by dampness and aggressive salts
-prevents the poured concrete from de-watering and drying out too quickly, affecting strength and cracking
What is propping?
Propping is a system of structural members used temporarily to support loads during construction
What does step cracking indicate?
Most commonly associated with
foundation issues
differential movement: different building materials expand or contract differently in reaction to changes in temperature and moisture moisture
bowing walls
What does vertical cracking indicate?
Heave
Settlement
Subsidence
What is a cover meter?
Identifies rebar in concrete
How do you know if a wall is a load bearing wall?
If walls on floors follow the same path
Refer to as built drawings
Thicker (300mm?)
What approved document would you use for sizing rainwater goods?
Doc H - table 1 and 2 - and BRE guides/BS
why would you need to ventilate a beam and block floor ?
To ensure there is not a build up of gases
