Building Pathology

Question 1

Defects in Commercial Property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Regents Street Disease

Answer 1

Defect - Regents Street Disease/ Deansgate Dilema occurs in buildings constructed
using a steel frame covered in facing masonry or stone. Often found in early twentieth
century buildings where large masonry or stone units were tightly built around the
steel frame. These porous materials allow moisture to get to the steel structure which
then corrodes. Corroded metals can increase up to 7 times their original size. This
puts pressure on the surrounding masonry causing cracking.

Identification — Cracking to masonry around the structural frame.

Remedy -

• Removal of external stone/masonry to repair steelwork - This process
  involves cleaning the exposed steelwork to remove the surface rust by either
  sand blasting or needle gunning and treating the exposed surface with an
  appropriate site applied protective paint coating. This is clearly expensive and
  highly disruptive. It normally only covers the exposed elevations of the steel
  frame so there is a risk that no all corrosion is treated. However, it does allow the
  structural engineer to assess the condition of the exposed steel and its structural
  adequacy and if necessary it can be removed and replaced.
• Cathodic Protection - CP relies on the passage of a DC current from the environment into the protected metal surface to reverse the direction of electric currents associated with the corrosion process. It does not make good previous corrosion but suppresses the continuation of the process.

Question 2

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

High Alumina Cement

Answer 2

Defect - 1954 — 1974 — HAC gives high early strength and was originally used in maritime applications. It is found mainly in Pre stressed Precast Concrete Beams. It undergoes a mineralogical change called conversion which increases porosity and reduces resistance to chemical attack. Therefore where water and chemicals are present it can cause the concrete to become friable and lead to a loss of strength.

Identification — The concrete becomes friable and can often turn a chocolate brown
colour and it is a particular issue in structural members such as roofs in warm moist
environments.

Remedy — For HAC there is no known cure or treatment. Any patch repairs and external
protective treatment can only delay the inevitable decay. Where HAC is identified its
strength should be assessed and monitored? A document known as BRAC (Building
Regulation Advisory Council) identify 3 stages of investigation: Identification, strength
assessment and durability assessment.

Question 3

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Carbonation

Answer 3

Defect — Carbonation occurs when the alkaline elements of the concrete react with the
atmospheric carbon dioxide creating calcium carbonate which lowers the PH level of the
concrete and therefore reduces the passivity of the concrete. It will cause gradual
neutralisation of the alkalinity from the surface inwards. Should there not be adequate
coverage of steel reinforcement within the concrete, carbon dioxide can react with the re-bar and cause corrosion.

Inadequate coverage, mix proportions cpmpaction. Temperature, humidity and CO2
levels can all affect the level of carbonation.

The rate at which carbonation occurs is inversely proportional to the square root of the
age of the building i.e. typical Portland cement concrete may show a depth of
carbonation of 3-5mm after 10 years.

Identification -A simple on site test can be carried out by using a simple alkali-sensitive
staining technique. Phenolphthalein will turn purple on unaffected concrete where it is still highly alkaline. No staining is observed where carbonation has reduced the level of alkalinity. A more robust technique is through petrographic analysis where a sample of the concrete is examined under a microscope.

Remedy — How is carbonation remedied?
Typical remedy is to remove the delaminated concrete, clean the re-bar by abrasive blast cleaning and patch in the concrete. A longer term and more expensive solution is to induce cathodic protection. This is where an external anode is connected to the metal and the passage of an electric current is used to stop corrosions.

Question 4

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Chloride Attack

Answer 4

Defect - Calcium Chloride Additive — Used as an accelerator mainly in the 1950’s and
1960’s (it was banned in 1977). Reduces the passivity of the concrete in damp conditions
leading to corrosion in the form of localised pitting of the rebar. The inclusion of calcium
chloride ion into concrete increases the electrical conductivity of the concrete and with this, the likely corrosion rates. Sufficient quantities of chloride ion can disrupt the passive layer around steel reinforcement, and if they exceed a threshold level can prevent the passive layer from being re-established.

However, whilst chlorides are no longer added to concrete as an admixture, they could
still be present as a result of poorly washed marine aggregates, or from exposure to deicing salts, salt spray, sea water and the like. Chlorides can be absorbed into the body of the concrete by processes of absorption and diffusion. Potentially, concrete affected by external contamination sources is likely to be at more risk of corrosion
Identification — Rust staining and delamination of concrete. Examination of the reenforcement bar will show signs of pitting where localized breakdown of the passive oxide layer has occurred. Occasionally the rebar may be completely eaten away leading to obvious structural concerns.

Remedy - Localised concrete repairs can be carried out, however if the original mixture
includes chlorides then it is likely that the corrosion will commence in another area. A longer term and more expensive solution is to induce cathodic protection. This is where an external anode is connected to the metal and the passage of an electric current is used to stop corrosions.

Question 5

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Alkiali Silica Reaction

Answer 5

Defect - Alkali silica reaction (ASR) is the most common form of alkali-aggregate
reaction. Concrete is a highly alkaline material and therefore any pore water within the
concrete will also be alkaline. In certain situations the alkaline water can react with the
silica in the aggregate to produce a gel. The gel takes in water, expands and can cause
concrete to crack or disrupt.

Identification - In unrestrained concrete, the cracks have a characteristic random
distribution often referred to as ‘map cracking’. In restrained concrete, the cracking tends to run parallel to the main reinforcing bars. In particularly active situations, the cracks may be bordered by a colourless gel. This leads to surface pop-outs and spelling. Petrographic examination is the only sure way of identifying the attack.

Remedy - Three conditions are necessary for ASR to occur: certain silica in the
aggregate, sufficient moisture, high alkalinity. Removal of moisture by repairing damaged rain water goods is the first measure. Removal of the delaminated concrete and an isolated patch repair may also be an alternative. Secondary structural reinforcement can also be introduced.

Question 6

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Filler Joist Floor

Answer 6

Defect - ‘Filler joist’ is an early form of floor slab construction, which was commonly used
between about the 1880s and 1920s. It was formed from iron or steel joists spaced
between 600 and 900mm apart and in-filled with unreinforced concrete. The concrete often had coke breeze in it acting as an aggregate. The cover on the steel joists was often insufficient. The coke releases acids which change the passivity of the concrete and the lack of cover increases the risk of carbonation. Both lead to corrosion of the steel joists, which in turn cause cracking of the concrete and brickwork. The lack of cover also poses the issue of lack of fire protection and strength.

Identification — Long cracks along the joists at approx 600/900mm centres.

Remedy — Expose the steel, remove the rust and treat with protective paint coating or
cathodic protection.

Question 7

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Woodwool Slabs

Answer 7

Defect - When used as permanent shuttering for concrete it may lead to grout loss,
honeycombing or voids. Therefore, can lead to reduced fire resistance, reinforcement
corrosion or loss of structural strength.

Remedy — Non-destructive testing techniques can be employed to identify whether any
problems are likely to exist, although physical sampling may be more reliable. Removal of the shuttering and repairs using hand placed mortars or sprayed concrete may be necessary if defects are found.

Question 8

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Brick Slips and Brick Panels

Answer 8

Defect - Popular in the 1960, and early 1970s, brick slips were seen as an easy method
of concealing the exposed edges of a concrete frame at each floor level. A failure to
recognise the propensity of a concrete framed building to shrink created circumstances
where the brick slips could be stressed and forced off the building, often with serious risks to health and safety. The provision of movement joints above and below the course of slips is essential, but great care is needed to ensure that even the smallest amount of
bridging of the soft joint does not occur. Brick panels within either exposed concrete
frames or supported on knibs can similarly be affected by unplanned shrinkage in a
concrete frame.

Remedy — Depends on the severity of the defect but in essence sufficient movement joints are required to take account of the different movements of the different elements.

Question 9

Defects in commercial property

What common defects affect commercial properties? Describe how you would identify them and potential remedial actions?

Sulphate attack or Delayed Ettringite Formation

Answer 9

Defect - Sulphate attack is a chemical reaction affecting concrete causing it to expand
and crack. Externally, this is due to penetration of sulphates in solution (i.e. in
groundwater) into the concrete from outside. Internally, this is due to a soluble source
being incorporated into the concrete at the time of mixing (i.e. gypsum in the aggregate)
or sulphates within the hardcore beneath the concrete. This can lead to heave of the slab and structural damage.

Remedy - It is often the case that the concrete will need to be dug up and replaced with a sulphate resist concrete.

Question 10

Roofs
What are the common defects associated with flat roofs?

Answer 10

Common defects associated with flat roofs include blistering and splitting of covering, sagging

(due to failure of decking between joists), ponding (due to insufficient falls), damages to
fleshings, inadequate solar protection.

Question 11

What are the typical defects of a flat roof? What are the remedies?

Answer 11

• Crazing
  Surface crazing is caused where there is a lack of adequate protection from the
  harmful effects of exposure to the sun or, in rare occasions, chemical attack. If this
  is only in small localised patches no treatment is necessary but should be regularly
  rechecked. If more widespread the areas will have to be re roofed and specialist
  protection introduced
• Ponding
  A minimum gradient of 1:40 is required for a flat roof to shed water effectively. Where
  the appropriate fall has not been built in or has been altered by structural movement
  `ponding’ is likely to occur. Where water is allowed to sit on the surface of a felt roof for
  an extended period its lifespan will be drastically reduced. Could also be due to
  blocked drainage.
• Thermal Movement
  Cracks, splits and rucks can occur when there is thermal or moisture movement between
  the roof substrate and membrane. It is likely that localised re-roofing will be necessary to
  tackle this using a high performance felt.
• Blistering
  Blisters can be caused by water vapour pressure occurring below the roof covering.
  The blister should be cut and then re-bonded to the underlay allowing any trapped
  moisture to escape first. The source of the moisture should also be traced and
  rectified.
• Flashings and Falls Around Openings
  Defect — Poor workmanship or deterioration of the flashing details around openings can
  lead to water ingress. Also porr detailing or construction of the structure can lead to
  structural movement around roof lights etc. Leading to ponding.
• People
  Punctures and rips are most often caused by impact damage by people or loose
  debris. They should be repaired using localised patch repairs.
• Cracks and tears along the line of the support joists
  Can be caused by thermal or moisture movement, saturation of insulation or sagging
  of the roof deck. This can be repaired by cutting back the existing felt and allowing the
  area to dry before applying a new layer of high performance felt with a suitable
  overlap between the new and existing material.

Question 12

Tell us about the methods of assessing flat roof defects you learned about?

Answer 12

Electronic leak detection whereby a weak electrical field is created on the dampened surface and any current that ‘earths’ into the building changes the nature of the field locally. This should pinpoint the penetration or just as importantly show when water penetration is not caused by a roof leak. Also Firstly a thermographic examination could y be carried out to identify areas of leaks.

Question 13

What should you take into account when deciding whether to repair or replace a flat
roof?

Answer 13

Its age and life expectancy, the overall condition i.e. are the defects localised or affecting the whole of the roof, what type of defect is it and does it relate to a localised factor or is it an issue with the whole roof, are they affecting the surface layer or the roof structure. Client’s intentions for the building, their budget, the building use, disruption caused and possible phasing required.

• Age
• Condition
• Extent of Defect
• Cost
• Use
• Life Cycle Costing
• Disruption associated with repair and replacement.

Question 14

You are asked to inspect a flat roof take us through the inspections process?

Answer 14

Firstly gather historical building information and details of any current or previous issues with the roof. Make arrangements for access and prepare necessary RAMS.
Firstly identify:
* Age
* Previous repairs
* Period defective for
* When does it leak
* Does water pond
* Use of room below
* Used as a balcony or terrace
* Access arrangements

Secondly carry out a visual inspection during or after rain

Question 15

Roof defects and repairs

Answer 15

Defect - Repair
Sign of previous repairs. - If leak in the same area may indicate poor repair, carry out proper repair. Many patches may mean general issue. May require
overlaying with new covering or replacement.

Punctured membrane. - Localised patch repair. If line of holes overlay with strip of high
performance felt.

Flowing, rippling, cracking or crazing. - Indicates old age particularly in asphalt.

Splits or ruckles. - Associated with substrate movement.

Blisters. - Entrapped water or condensation. If small inspect regularly. If growing further investigation of condensation or water ingress needed. Large blisters should be cut allowed to dry out and then patch repair.

Have lap joints pulled or lifted. - Problem with old roof membranes in severe cases remove old roof coverings and replace with high performance felt.

Is roof covered with chippings, reflective paint or mineral surface. - Solar reflective paint should be renewed every 5 years. Chippings may have blown.

Ponding or surface water. - Ponding can be tolerated by high performance felts and mastic asphalt but can reduce longevity of all waterproof coverings and can indicate other serious issues.

Excessive deflection, springiness or sponginess in the roof. - Structural repairs may be needed.

Blockage in gutters or roof outlets. - Drainage problem. Standing water can lead to water ingress around fleshings etc.

Signs of movement between roof and main. - If yes reform edge details using high performance felt.

Question 16

What is damp?

Answer 16

A building is only considered to be damp if the moisture becomes visible through discoloration and staining of finishes or causes mould growth, sulphate attack, frost damage or even drips and puddles

Question 17

How can you test for damp?

Answer 17

The use of a protimeter I moisture meter or a Speedy Carbide Meter can be used to establish the moisture content of walls, and the level of damp occurring.

Question 18

What is a protimeter / moisture meter?

Answer 18

A protimeter works by measuring the electrical resistance between two applied electrodes. Protimeters are generally used to monitor the moisture content in wood, therefore when used on other materials, the actual readings may be misleading but does give a sense of moisture content.

Question 19

What is a Speedy Carbide Meter?

Answer 19

A speedy carbide meter is a device to measure moisture in masonry through slow drilling masonry and putting dust into a sealed container with a known measurement of calcium carbide. It releases a gas in proportion to the amount of moisture present

Question 20

How would you identify rising damp? What are the causes? How would you remedy it?

Answer 20

RISING DAMP - -Inn high tide mark, peeling and blistering of wall finishes, musty smell, rotting of timber, hyproscopic salts. Use of Speedy carbide meter to measure moisture. The readings withmoisture meter result in high surface readings, often with slight decline, finishing with a sudden cutoff

CAUSES — No damp proof course, DPC bridged by pointing, render, soil, paving, mortar
droppings, affects both solid and suspended floors.

REMEDY — Remedy DPC problems, remove bridging of DPC, chemical injected DPC

Question 21

State and Describe 3 Remedies for Rising Damp.

Answer 21

Rising damp is caused either by the lack of a damp proof course, a defective damp proof
course or external features bridging the damp proof course. The remedy therefore involves removing the external feature, the injection of water repellent chemicals into the brick work or the fitting of a new physical damp proof membrane. Where a damp proof course is not suitable lime plaster and wash can be used to minimise the damage caused to the internal finishes.

Question 22

How would you identify penetration damp? What are the causes? How would you
remedy it?

Answer 22

PENETRATION DAMP — dependant upon the levels of exposure of the building and often penetration only occurs in certain areas. The first sign of damp penetration is often the appearance of damp patches on walls, ceilings or floors. These tend to grow or darken after periods of heavy or prolonged rain.

CAUSES — Rain driving through exposed masonry walls that have insufficient thickness,
problems with cavity trays, cracked or detached rendering, defects to window cills, blocked cavity ties

REMEDY — Repointing of defective mortar joints, apply masonry water repellent, make good defective joint details, inspect cavity tray and cavity ties for blockages, inspect areas of roofs such as chimneys, parapets and thresholds

Question 23

What is a cold bridge?

Answer 23

A cold bridge is created when materials that are poor thermal insulators come into contact, allowing heat to flow through the path created, although nearby layers of material separated by airspace allow little heat transfer. Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging; the bridging has to be eliminated, rebuilt with a reduced cross-section or with materials that have better insulating properties, or with an additional insulating component, called a thermal break.

Question 24

How would you identify condensation? What are the causes? How would you remedy it?

Answer 24

CONDENSATION — The temperature of the air depends on how much water vapour it can carry. Hot air is able to carry more moisture and when this hot air hits a cold surface it loses some moisture as condensation. This water vapour comes from breathing, domestic activities such as cooking and bathing. It can lead to staining at cold bridges, peeling wallpaper and mould growth.

CAUSES — lack of insulation, lack of ventilation, unheated areas of the building.

REMEDY — reduce moisture generation, provide adequate ventilation, provide adequate
heating, improving the building insulation

Question 25

Condensation causes and remedial measures?

Answer 25

Causes - Condensation is caused by hot air carrying moisture hitting a cold surface and the moisture condensing on that surface. It is an issue in occupied premises often in areas of cooking or bathing. It can lead to staining, peeling of surface finishes and mould growth at cold bridging points.

Remedial Measures - Provide mechanical ventilation to the affected spaces, reduce moisture generation, provide adequate heating, install insulation or thermal breaks to remove the cold bridges.

Question 26

How long would you leave the brick / plaster to dry out before commencing work?

Answer 26

You need to allow time for the brick to dry out before commencing works. A de-humidifer can speed up the process, however a minimum of 3-4 months is recommended.

Question 27

Discolouring @ 450 x 900mm centres in a grid formation? Remediation?

Answer 27

This describes lateral damp ingress, from defective or blocked cavity ties. This is usually due to mortar dropping onto the cavity tie, thus making the drip ineffective. This allows penetration damp to occur.

Question 28

How would you tell the difference between rising damp and condensation with a
moisture meter

Answer 28

Rising damp is damp that comes up from the ground and only extends up to 1rn up the wall. Therefore if you take readings at 300mm centres going up the wall from the bottom and it is damp at the bottom and becomes increasingly less damp as you go up the wall to the point where it is not damp above the lm mark then it suggests rising damp.
Condensation would cause uniform dampness and is most often found at high level in corners where the hot air has risen and then condensed on the cold surface in a poorly ventilated corner of the room. Condensation has distinctive mildew which forms black spots.

Question 29

What ways could moisture enter the building? How would you differentiate between the
different types?

Answer 29

Penetrating damp — moisture gets into the building because there is a porous bridge
transferring moisture by capillary action from the external face of the walls to the internal face of the walls. Could be a single skin of masonry, water trapped behind render, mortar snots on cavity ties etc. Or there is a hole in the roof which allows moisture in through and it gets to the ceiling due to the force of gravity. I would identify it based on its location further investigation of the cause of the moisture.

Rising damp — Moisture rising up the wall from the ground due to capillary action normally up to a maximum of lm high tide marks. Identify through a visual inspection of its location and extent and also use moisture meter to confirm that the moisture content starts off high and gets lower before cutting off at approx 1 m. Identify if there is a DPC is something bridging that DPC. Ensure there are no other possible causes.

Condensation — Hot moist air hits a cold surface and condenses causing the surface to absorb the moisture which encourages staining and mildew growth. Identify it through the distinctive mildew, the location poorly ventilated areas with high humidity, kitchens, bathrooms, bedrooms, rooms used for drying clothes.

Question 30

What are the forms of damp repair?

Answer 30

Pentrating damp - identify the cause of the moisture and eliminate that cause. Replace
damaged plaster.

Rising damp — identify the lack of, defect or bridge affecting the DPC and remedy that by removing the bridge or injecting chemical DPC. Another alternative is to accept that the building as constructed with solid masonry and no DPC and use a lime plaster and paint finish which can deal with the moisture better than gypsum and modern paints.

Condensation — improve ventilation, reduce the moisture, remove the cold bridge.

Question 31

You are inspecting a building and identify a number of cracks in the external wall take me through your thought process?

Answer 31

I would firstly note the material the wall is constructed from and what form of
construction the building is. If there are any local factors which could be causing the
cracking such as trees or stumps, if there have been any alterations to the building, if there are drains in the vicinity of the crack. If there have been any alterations to the
building such as extensions, room in the roof or internal layout alterations.

Question 32

What other sorts of cracks would you expect to see on a brick building and what might
have caused them?

Answer 32

Subsidence — A movement down in the ground level. In clay soil, the growth of large trees which remove water from the ground can cause this. This leads can lead to vertical cracking if in the centre of the building or diagonal cracking if at the corner of the property. The cracks will be larger at the top and thinner at the bottom.

Heave — A movement upwards in the ground level. In clay soil the removal of a tree will lead to an increase in the moisture content of the soil which will cause the soil to swell. This leads to vertical cracking if in the centre of the building or diagonal cracking if at the corner of the property. The cracks will be larger at the bottom and thinner at the top.

Settlement — A movement down due to an increased load. Buildings will settle when first constructed or if there is a change in the load as the new load settles to the bearing capacity of the soil.

Differential Settlement — If two sections of a building are constructed off different foundations or the ground is made up of different soil types or strata then one may settle more than another causing cracking between the two sections of the building. Most common with extensions.

Thermal movement — Either expansion or shrinkage of the masonry, is often characterised by vertical cracks with a relatively constant width if appropriate expansion joints are not present

Lintel failure — Lintel failure allows a triangular section of brickwork above the window to drop down creating a triangular crack from the corner of the window toward the centre.

Corroded Steel lintel — Where a steel lintel has been used above an opening and the edge is exposed or close to the surface this can corrode over time and expand causing cracking.

Cavity wall tie failure — corrosion of large steel fishtail ties will lead to cracking every 4 or 5 courses as the steel expands.

Internal alterations - Where a wall has been removed and a steel beam put in its place without consideration to the increased load acting upon wall the beam is bearing upon. Or where a staircase has been moved without thought to the lateral restraint of the flank wall.

Question 33

What size cracks are of concern?

Answer 33

Up to 2mm — very slight / aesthetic

2mm-5mm — slight / aesthetic

5mm-15mm — moderate /serviceable

15mm-25mm — severe / serviceable

Over 25mm — very severe / stability

Question 34

Please describe the directional pattern of a crack caused by expansion of brickwork
horizontally to a wall. Would the cracking be evenly spaced throughout or
increase/decrease in width at one end?

Answer 34

Thermal movement causes the bricks to expand and shrink. This leads to vertical
cracks with a relatively constant width if appropriate expansion joints are not present.

Question 35

If there was stepped cracking on the corner of a building, what might have caused it?

Answer 35

Settlement, subsidence, heave

Question 36

What if the cracks were on concrete?

Answer 36

I would consider the common concrete defects such as Carbonation, HAC, Chloride Attach, Alkalai Silica Reaction etc. As well as issues relation to structural movement and poor design and construction.

Question 37

Crack between bay window and main wall — Possible causes and remedies.

Answer 37

Differential settlement caused by differences in the foundation depths between the main wall and the bay window. Confirm if movement is continuing if so then underpin the bay to similar depth. Possible things to look out for are differences in the soil, high water course, defective drain that could be causing subsidence to the bay.

Question 38

What type of soil is susceptible to heave and what are the possible causes?

Answer 38

Cohesive soils such as clay. Possible causes include removal of trees, change in water table, leaking drains or inadequate foundations that are built within the movement zones.

Question 39

Flank wall bulging full over its full height. Possible causes?

Answer 39

A possible cause is the lack of lateral restraint in the wall. If the floor joists are running from the front to the back of the house then there may be nothing connecting the flank wall to the building at the first and second floor levels. This may be due to poor design or some alteration in the internal layout such as a change in position of the staircase. Other potential causes to consider include cavity wall tie failure or increased roof load.

Question 40

Foundations can subside or heave. Name some reasons.

Answer 40

Heave — Usually in cohesive soils such as clay. Possible causes include removal of trees,
change in water table, leaking drains or inadequate foundations that are built within the
movement zone.

Subsidence - In all soil types. Differences in the type of soil leading to differences in the bearing capacity, a change in the water course or high water course, defective drain, voids in ground collapsing. Growth of trees removing water from the soil.

Question 41

What types of timber defects are there?

Answer 41

The main timber defects are dry rot and wet rot, insect attack

Question 42

Describe the different types of rot and how you would recognise them.

Answer 42

Dry Rot — Wood shrinks and splits into large cuboidal cracking, the wood is light in weight, crumbles under fingers and has a dull brown colour, cotton wool type mycelium is often visible grayish in colour when wet and yellow/purple when dry, strands are brittle when dry, a fruiting body can also occur with a reddish brown colour, only incurs inside of buildings.

Wet Rot — Wood shrinks and splits on a smaller scale, wood becomes darkened, mycelium can be white, brown, amber, green or black, strands are flexible when dry, the fruiting bodies can be a number of different colours can occur both inside and outside.

Question 43

What are the remedial measures to dry/wet rot?

Answer 43

Locate and eliminate the sources of moisture, promote rapid drying, remove rotted wood (450mm beyond last indications of rot and burn), surface application of fungicidal fluid, introduce support measures if required.

Question 44

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?

Answer 44

Typical indications of dry rot include:

• Wood shrinks, darkens and cracks in a ‘cuboidal’ manner.
• A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow often develops under less humid conditions. This ‘skin’ can be peeled like a mushroom.
• White, fluffy ‘cotton wool’ mycelium develops under humid conditions. ‘Teardrops’ may develop on the growth.
• Strands develop in the mycelium; these are brittle and when dry and crack when bent.
• Fruiting bodies are a soft, fleshy pancake or bracket with an orange-ochre surface. The surface has wide pores.
• Rust red coloured spore dust frequently seen around fruiting bodies.
• Active decay produces a musty, damp odour.
• Only occurs in certain conditions with 20-40% moisture content.

Therefore identifying and removing the cause of moisture is key to eradicating the rot. Any affected timbers should be removed and replaced with pre-treated timber. Any remaining timbers at risk of being affected by the dry rot should be treated with an effective fungicide. Where the dry rot has passed through the masonry, it should be isolated using physical containment and/or masonry sterilisation.

Question 45

Ends of the joists in a timber floor built in an external wall have been seriously affected by wet rot. How will you recognise this type of rot and what action would you take to resolve the problem?

Answer 45

Wet Rot requires high moisture contents of around 50-60% to propagate and spread, it is usually found in areas where there may be a water leak, or building failure, such as along window cills and in roof voids.

Indications of a Wet rot outbreak include:

• Surface cracking — cracks follow timber grain.
• Hyphae strands are thread like brown, yellowish, becoming darker brown in colour. (Key difference distinguishing from Dry rot)
• Distinctive fruiting body — (Although rarely found), thin sheet like shape, knobbly and olive brown surface.
• Infected timber turns dark brown in colour
  The first step to remedying Wet and Dry Rot is to find and eliminate the source of dampness, rectifying those faults that have contributed to the problem to prevent timbers becoming damp.

All infected and/or damaged timber should be removed, as these may be structurally impaired due to the decaying action of the Wet Rot and the remaining timber treated with a suitable preservative.

If the Wet Rot is in a confined space, such as a cupboard or loft space, it may be necessary to consider methods to improve the ventilation

Question 46

What are the remedial measures for Dry Rot?

Answer 46

Remedial action for Dry Rot is far more intrusive. The first step is to establish the full extent of the outbreak, many parts of which may be initially concealed from view, underneath floorboards, behind furniture, panels removed etc.

Affected timber, similar to Wet Rot needs to be cut out and replaced, including those within approximately 300-450mm beyond, to allow for possible further contamination. All surrounding timbers should be treated with a chemical biocide, to ensure all strands/ spores are killed off. It is imperative, that you ensure the timbers do not become re wetted at this stage, as this would invalidate any insurance or guarantee for the Dry Rot treatment.

Affected plaster that has come into contact with the Dry Rot needs to be removed, and wall surfaces treated with a sterilizer or biocide.

Lastly, the area should be kept dry and heated, to ensure all timbers are fully dried out to prevent or reduce the likelihood of further outbreaks.

Question 47

Explain the life cycle of a rot?

Answer 47

The 4 main dry rot lifecycle stages are as follows:

1. Spore: Spores are omnipresent. In very large numbers dry rot spores appear as a
   fine orange brown dust. The spore are activated when combined with timber and
   moisture.
2. Hyphae: Where timber and moisture are present the spore will produces very fine
   white strands called hyphae, which allow the dry rot fungus to grow by feeding on the
   timber. Thereby breaking down the structure of the timber while it grows to form a
   mycelium
3. Mycelium: The resulting hyphae mass is known as mycelium. Mycelium has the
   ability to grow over a significant distance and a variety of materials, which allows an
   outbreak to progressively destroy the structural timbers of an entire building if left
   undetected.
4. Fruiting Body: To perpetuate itself the fungus will create a fruiting body
   (sporophore). This mushroom-like forms function is to pump out spores into the
   atmosphere that can be transferred by air currents to other susceptible areas within the
   building allowing them to germinate and create a new attack of dry rot, thus bringing us
   back to the beginning of the dry rot lifecycle.