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1. Building Pathology > 01 Dampness > Flashcards

01 Dampness Flashcards

1
Q

How does water enter buildings?

A
  1. Condensation
  2. Penetrating dampness
  3. Rising dampness
  4. Leaks (e.g. from pipework)
  5. Trapped construction water (new builds)
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2
Q

Describe the main consequences caused by dampness within buildings.

A
  1. Health hazard
  2. Reduce strength of building materials
  3. Cause movement in building elements
  4. Lead to timber decay (dry and wet rot, insect attack)
  5. Cause chemical reactions in building components
  6. Reduce effectiveness of insulation
  7. Damage decorations
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3
Q

How can you record damp in buildings?

A
  1. Oven Drying (Gravimetric Testing)
  2. Conductance Meter (aka Protimeter)
  3. Carbide Testing (aka Speedy Meter)
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4
Q

Explain the process of oven drying to measure damp.

A
  1. Sample is weighed, dried in an oven and then weighed again
  2. Moisture content = (wet weight - dry weight x 100) / dry weight
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5
Q

Explain how a conductance meter can be used to measure dampness.

A
  1. When materials absorb water, they can conduct electricity
  2. Conductance meters have two metal probes (electrodes) which are firmly pressed into the material being tested
  3. Electrical resistance between the two probes can then be measured
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6
Q

Explain how carbide testing can be used to measure damp.

A
  1. Used for masonry products (e.g. bricks, blocks, mortars etc.)
  2. Material is drilled slowly to minimise heating (and thus drying) then weighed and placed in a container
  3. Specific amount of calcium carbide is added and container is sealed
  4. Container vigorously shaken so two materials mix
  5. Moisture in sample reacts with calcium carbide to produce acetylene gas, causing pressure inside the container, which gives a reading on the pressure gauge
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7
Q

Explain some of the limitations of oven drying to measure damp.

A
  1. Destructive
  2. Little practical use on site
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8
Q

Explain some of the limitations of using a conductance meter to measure damp.

A
  1. Calibrated for timber, so not accurate for other materials (only comparative readings)
  2. Readings may be higher if timber has been treated with water-based preservatives
  3. Electrical conductive surfaces (e.g. aluminium foil-backed wallpaper) may cause inaccurate readings
  4. Only surface readings can practically be taken (deep probes with insulated sides needed otherwise)
  5. Salts naturally present in walling materials conduct electricity and can be confused with damp problems
  6. Hygroscopic salts left by previous dampness may cause high reading, not necessarily ongoing damp problems
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9
Q

Explain some of the limitations of carbide testing to measure damp.

A
  1. Knowledge of material being tested is required as different materials will differ in the amount of moisture they can contain and still be regarded as ‘dry’
  2. Destructive - requires several readings for accuracy
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10
Q

What guidance is available in relation to dampness in buildings?

A
  1. BRE BR 466 - Understanding Dampness
  2. BS 5250:2011 - Code of practice for control of condensation in buildings
  3. BRE Digest 245 - Rising Dampness in Walls: Diagnosis and Treatment
  4. BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs
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11
Q

What is condensation and how is it caused?

A
  1. Condensation - change of water vapour naturally present in air into liquid water
  2. The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
  3. If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
  4. Once the air falls to a temperature where it can no longer hold the amount of water vapour present (i.e. it becomes saturated), liquid water will form on the cold surface
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12
Q

What is meant by the terms ‘dew point’ and ‘relative humidity’?

A
  • Dew point - the temperature at which the air becomes saturated and will condense
  • Relative humidity - moisture content present within the air, referred to as a percentage of the amount of water vapour it can hold at that temperature
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13
Q

How does modern living standards affect the occurrence of condensation within buildings?

A
  1. Double-glazed windows can create a more ‘sealed’ building that lacks adequate ventilation
  2. Trickle vents in windows (where present) are often kept closed
  3. Balanced flue boilers (instead of open fires) reduce natural ventilation
  4. Central heating systems are often used intermittently, meaning cold surfaces may coincide with high humidity levels
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14
Q

What problems are associated with condensation?

A
  1. Mould growth, particularly where RH remains above 70% for long periods (usually more than 12 hours)
  2. Health risks to the elderly, young children, asthmatics and those with weakened immune systems
  3. Can encourage timber decay where timbers are sublect to prolonger moisture exposure
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15
Q

How would you identify condensation within a building?

A
  1. Wall has a ‘misty’ surface
  2. Stains or streaks of water runnin gdown a wall (particularly in bathrooms, kitchens and below windows)
  3. Damp patches with no definitive edges
  4. Dampness behind wall cupboards or inside wardrobes against external walls (areas where air circulation is restricted)
  5. Localised dampness at potential ‘cold bridges’
  6. Patches of mould growth
  7. Humidity (measured using a hygrometer), insulation and ventilation levels as well as heating and living patterns must also be taken into account
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16
Q

What steps would you recommend to eliminate condensation?

A
  • Short term - mould-affected areas can be washed using a fungicidal or bleach solution - do not use water as this will just spread the mould
  • Long term - combination of the following:
    1. Reduce moisture generation (lids on pans, dry clothes outside, vent tumble dryers externally, do not use paraffin or bottled gas heaters, put cold water in bath before hot)
    2. Increase ventilation to remove moisture-laden air (open trickle vents, open windows, mechanical ventilation)
    3. Increase air temperature by heating - warmer air can hold more water vapour without condensing
    4. Increase surface temperature by thermal insulation (external or internal)
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17
Q

What is interstitial condensation and how would you deal with it?

A
  1. Interstitial condensation is condensation that occurs within the structure of an element, as opposed to on its surface
  2. If the internal surface temperature is above the dew point but the interior temperature of the element is below the dew point, water vapour will condense inside the element rather than on its surface
  3. If it occurs in a material such as timber, action will be needed to prevent risk of rot, usually by installing additional wall insulation
  4. If internal inuslation is added, a vapour barrier must be provided on the warm side of the insulation to act as a barrier to interstitial condensation
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18
Q

What are the health risks associated with the presence of mould in buildings?

A
  1. Moulds produce allergens, irritants and sometimes toxic substances, so inhaling or touching mould spores can cause allergic reactions (e.g. sneezing, runny nose, red eyes, skin rash etc.) and respiratory problems (e.g. asthma attacks)
  2. There is contradicting research that certain toxigenic moulds can cause rare health conditions such as bleeding in the lungs - research is ongoing
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19
Q

To avoid mould growth, what level should the relative humidity be kept under?

A

70%

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20
Q

What guidance is available in relation to condensation in buildings?

A

BS 5250:2011 - Code of practice for control of condensation in buildings

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21
Q

What is penetrating damp?

A

Water that ingresses through the structure of a building

22
Q

What are the different mechanisms of water ingress relating to penetrating dampness?

A
  1. Gravity
  2. Capillary action
  3. Surface tension
  4. Kinetic energy (splashing)
  5. Wind force
  6. Differential air pressure (inside and out)
23
Q

What are the common causes and routes of penetrating dampness?

A
  1. Slipped roof tiles
  2. Inadequate chimney/parapet flashing
  3. Copings without drips or not bedded on DPCs
  4. Leaking gutters (lack of correct support, damaged joints, lack of regular clearing)
  5. Overflowing hopper heads
  6. Leaking downpipes (broken joints, rusting cast iron downpipes to rear against wall)
  7. Continuously running cistern overflows (not discharging water clear of wall)
  8. Blocked gulleys (resulting in water splashing against wall)
  9. Cracked render or movement cracks in brickwork
  10. Defective pointing (recessed joints that could lead to frost action)
  11. Cavity ties (upside down so drip ineffective, mortar droppings resting on ties, uneven courses resulting in ties sloping toward inner leaf)
  12. Inadequately fixed cavity insulation boards causing bridging of the cavity from outer to inner leafy
  13. Poorly fitted windows and doors
  14. Sills without drips
  15. Poorly designed thresholds
  16. Missing vertical DPCs
  17. Driving rain on solid walls in particularly exposed situations (on cliff sides/west side of the Pennines)
  18. Vegetation growth to damp/shaded brickwork
  19. Repointing older buildings with cement mortar - stronger but less breathable than lime mortar, reducing the rate of evaporation. Also not as flexible so more likely to crack through drying shrinkage, thus allowing water ingress
  20. Applying strong external renders (for the same reasons as using strong mortars)
  21. Walls built in denser materials (e.g. granite or engineering bricks) - lack the ability to absorb water so most water runs down the face, which makes minor cracks more critical in allowing moisture ingress. Evaporation is also restricted
24
Q

What problems are associated with penetrating damp?

A
  1. Lead to outbreaks of dry or wet rot under the right conditions
  2. Reduce the strength of building materials, such as chipboard and plasterboard
  3. Cause chemical reactions in building components (e.g. sulphate attack)
  4. Reduce the effectiveness of insulation
  5. Damage decorations
25
Q

How would you identify penetrating damp within a building?

A
  1. Distinct damp patches with well-defined edges
  2. Often in localised areas
  3. Moisture readings show sharp change from wet to dry
  4. Patches of efflorescence (crystallisation of sulphates and carbonates present in building materials)
  5. Timber in area of damp has high moisture content
  6. External inspection may reveal obvious defects (e.g. cracked render/brickwork, damaged downpipes etc.)
  7. Deep wall probes indicate high readings in centre of wall
  8. Line of dampness on internal plasterwork corresponding with mortar joints where cement mortar/dense wall materials have been used
  9. Measure wall temperature, air temperature and RH to eliminate condensation
  10. Salt analysis shows zero level of nitrates and chlorides, eliminating rising damp
26
Q

What steps would you recommend to eliminate penetrating damp?

A
  • Identify the source of penetrating damp and remove or provide a barrier, for example:
    • Replace defective rainwater goods
    • Introduce DPCs beneath copings or vertical DPCs around openings
    • Repair cracked render/brickwork
    • Unblock gulleys/rainwater goods
    • Replace poorly installed cavity ties
  • Application of a hydrophobic masonry paint (repels water but still allows the wall to breathe) may also be beneficial for solid walls that experience excessive rain penetration
27
Q

What is rising damp and how is it caused?

A
  • Ground water rising by capillary action through pores of the wall or floor material
  • Causes:
    1. Lack of DPC/DPM
    2. Inadequate lapping of DPC/DPM
    3. Bridging of an existing DPC/DPM (often by external rendered finishes or raised ground levels)
    4. DPC/DPM failure through natural deterioration or damage caused by building movement
    5. Splashing from rain or downpipes where DPC is less than the recommended 150mm above ground (Approved Document C)
    6. Increase in ground water levels (e.g. man-induced changes to the water table, leaking drains, blocked land drainage systems, leaking water mains and springs) - likely if rising damp occurs fairly suddenly
28
Q

What height can rising damp reach and what factors can affect this?

A
  • Rarely higher than 1.5m
  • Depends on:
    1. Supply of water
    2. Pore structure of materials
    3. Rate of evaporation
    4. Heating within building
    5. Chemicals in ground and walls - efflorescence can block capillaries through which water evaporates, thus driving water further up the wall
29
Q

What problems are associated with rising damp?

A
  1. Lead to outbreaks of dry or wet rot under the right conditions
  2. Reduce the strength of building materials, such as chipboard and plasterboard
  3. Reduce the effectiveness of insulation
  4. Damage decorations
30
Q

How would you identify rising damp within a building?

A
  1. Visual inspection of possible causes (lack of / bridging of DPC/DPM etc.)
  2. Characteristic tide mark that does not extend beyond the lower part of the wall
  3. Damp contours can be pinpointed with a moisture meter
  4. Damp limited to usually 1m-1.5m above ground and readings above peak will drop quickly
  5. High percentage of moisture content in timber skirtings
  6. Salt analysis using a calcium carbide meter determines a high level of nitrates and chlorides, which are contained naturally in the subsoil
  7. Areas of dampness appear to get wetter in humid conditions due to hygroscopic salts (nitrates and chlorides) brought up from the ground, which attract water in from the atmosphere
  8. BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) contains detailed guidance on rising damp identification and remediation
31
Q

What steps would you recommend to eliminate rising damp?

A
  • Identify the source of rising damp and remove or provide a barrier, for example:
    • Lower the ground level (where DPC is breached or ground level is not 150mm below DPC)
    • Repair leaking drains/water mains
    • Unblock land drainage systems
    • Replace DPC or provide new where non-existent
  • Replace plaster/finishes where hygroscopic salts may still be present
    • Renew to height 300mm above level of rising damp
    • Re-plaster with a cement-based plaster (not gypsum plaster as most of these cannot prevent the passage of hygroscopic salts and quickly breakdown in wet conditions), preferably containing a waterproofer or salt inhibitor
32
Q

What different methods of installing/replacing DPCs are available?

A

Installation of any type of DPC must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works:

  1. Physical replacement - more expensive, disruptive and can only be laid on horizontal course (not suitable for rubble walls)
  2. Chemical injection - cheaper, lines the pores with a water-repellent solution (usually silicone/latex) however effectiveness depends on its successful penetration of the wall and lack of ‘viscous fingering’ (chemical spreads out and does not form a continuous barrier)
  3. Electro Osmotic DPC - a titanium wire (anode) is secured around the wall at DPC level and connected to a small power supply, which causes moisture molecules to repel down the wall back into the ground (not supported by the BRE)
33
Q

What guidance is available for rising damp problems?

A
  1. BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) - rising damp identification and remediation
  2. BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs
34
Q

What methods can be used to minimise dampness within a basement?

A
  1. Dense Monolithic Concrete
  2. Cementitious Tanking
  3. Mastic Asphalt Tanking
  4. Bund Wall System
  5. Drained Cavity System
35
Q

How is dense monolithic concrete used to waterproof a basement and what are its main disadvantages?

A
  1. Walls and floor are constructed from high quality dense monolithic concrete to form a watertight barrier
  2. May not always be water vapour proof so some form of lining (tanking) may be required
  3. Only applies to new-builds
36
Q

What is the difference between cementitious tanking and mastic asphalt tanking?

A

Cementitious Tanking:

  1. Certain additives are added to a cement based medium and applied to the base slab and walls
  2. Not very good at withstanding substantial levels of hydrostatic pressure

Mastic Asphalt Tanking:

  1. Provides a continuous waterproof membrane applied to the base slab and walls
  2. Can be applied internally or externally depending on the circumstances on site (i.e. external may not be possible in existing buildings)
  3. Membrane needs additional protection by building an inner skin wall backfilled to keep the membrane adhered to the earth-retaining wall
37
Q

What are the disadvantages of using tanking as a method of waterproofing a basement?

A
  1. Water is not drained, merely pushed to other areas around the structure, which could cause problems elsewhere
  2. Only external tanking will protect the structure from aggressive sulphates that may be present in the surrounding soil, which is not always possible
38
Q

What is a bund wall and how can it be used as a method of waterproofing a basement?

A
  1. Construction of an inner non-load bearing wall to form a cavity joined to special triangular tiles laid to falls
  2. This enables moisture to collect in the cavity and drain away into a sump, where it can be pumped into the surface water drainage system
  3. Cavity should be ventilated
39
Q

What is a drained cavity system and how can it be used as a method of waterproofing a basement?

A
  1. Plastic membrane in an egg-crate type formation applied to the wall and floor with properly bonded overlap joints in one continuous system
  2. Allows air and moisture to circulate and drains water into a sump, where it can be pumped into the surface water drainage system
40
Q

What guidance is available for waterproofing basements?

A

BS 8102:2009 ‘Protection of Below Ground Structures against Water from the Ground’

41
Q

How would you differentiate between rising damp and penetrating damp?

A

For rising damp:

  1. Positive salt analysis (containing nitrates and/or chlorides)
  2. Visible tide mark to lower part of wall
  3. Limit of dampness usually 1m-1.5m above ground
  4. Moisture readings quickly drop above tide mark
  5. Areas of dampness appear to get wetter in humid conditions (due to hygroscopic salts drawn up from the ground)
  6. External inspection may indicate missing or bridged DPC
42
Q

How would you differentiate between penetrating damp and condensation?

A

For penetrating damp:

  1. Moisture content is usually localised/isolated
  2. Moistures readings identify an epicentre of the water entry
  3. High moisture content within fabric of element, not just on its surface
  4. Evidence of an external defect (e.g. wall cracking, defective downpipe etc.)
  5. Measure wall temperature, air temperature and RH to eliminate condensation
  6. Mould growth unusual
43
Q

How would you differentiate between rising damp and condensation?

A

For condensation:

  1. Water is usually on the wall face when wiped with hand
  2. Negative salt analysis (no nitrates or chlorides)
  3. Moisture readings may occur across the full height of a wall (although higher readings at lower levels as warm air rises so less chance of condensation)
  4. Moisture content of skirting normal but may contain staining due to water run-off
  5. Deep wall probes indicate low readings in centre of wall
  6. Mould growth likely
  7. Surface temperature is below dew point temperature (established by measuring air temperature and RH)
44
Q

What are hygroscopic salts and are they problematic?

A
  1. Salts that absorb moisture in from the air
  2. As they absorb water, they continually re-dissolve, which prevents any crystallisation
  3. Often associated with rising damp, as nitrates and chlorides (both of which are hygroscopic) naturally present in sub-soil are drawn up through the wall with water and are left behind on the surface once the water evaporates, causing surfaces to become wetter from moisture in the air as well
45
Q

What is efflorescence and is it problematic?

A
  1. Temporary white powdery substance often seen on the face of new brickwork and in cases of rising damp
  2. Caused by sulphates and carbonates naturally present in building materials crystallising as water evaporates, due to their relatively insoluble nature
  3. These salts are not hygroscopic and merely indicate that moisture is evaporating from the structure
  4. They may only be problematic in cases of rising damp, as the crystals can sometimes block pores in brickwork, thus preventing evaporation and driving damp higher up the wall
  5. Can be brushed off if appearance is causing a concern
46
Q

What is cryptoflorescence and is it problematic?

A
  1. Crystallisation of salts (often magnesium) below the surface of the brick
  2. Can cause spalling where old, relatively weak bricks are re-used inappropriately, particularly in areas of excessive dampness
  3. Can also occur through salts deposited by the run-off from limestone or from air pollution
  4. Damage can also occur where bricks are covered by a surface treatment (as salts may crystallise behind it)
  5. The effect on the bricks is similar to that caused by frost attack
47
Q

How do you test to establish if service pipes are leaking?

A

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48
Q

What is the adverse effect of well-insulated buildings?

A

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49
Q

When carrying out a survey of a Victorian house, what potential pathology issues could lead to damp problems in the building?

A

???

50
Q

What problems are associated with vegetation growth to damp/shaded brickwork?

A

Can retain moisture and cause pentrating dampness

51
Q

What measures should be adopted to repair a property affected by flooding?

A

???

52
Q

What would be required from a damp specialist before you recommended them?

A

Must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works

1. Building Pathology (7 decks)

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