BUILDING PATHOLOGY : COMMON DEFECTS (PART 1)

TIMBER DEFECTS
1. Beetle rot
2. Dry / wet rot
  1. Causes
    1. Species of timber
    2. Chronic dampness
    3. Poor ventilation
    4. Normal internal temperature
  2. Effects / signs
    1. Sound hollow and dull
    2. Be of abnormal colour
    3. Wood disintegration
    4. Fungi
      1. Dry rot
        Brown
        Cubical
        Fluffy
        Yellow mycelium
        Musty smell
        Will not grow in saturated conditions
        Red spores
      2. Wet rot
        Less pervasive and harmful generally
        Minimum moisture content of 20%
        Produces cubical failure in wood similar to dry rot
        Olive green / brown fruiting body
        Affected timber darkened
        Surface may appear to be sound
DAMP
1. Rising damp
  1. Moisture present in ground below walls rising up through fabric of wall
    1. Capillary action
  2. Below ground moisture sources
    1. Free water in subsoil (water table)
    2. Water main breach
    3. Build up from drain / pipe leaks
  3. Investigation using trial holes
    1. Confirm existence of DPC which may be concealed
    2. Verify construction of walls below ground
    3. Establish height of water table
  4. Chemical analysis
    1. Can confirm that salts present could only have been derived from below ground sources.
  5. Causes
    1. Defective DPC
    2. DPC bridging
    3. No DPC
  6. Characteristics
    1. 'Tide line' of yellow / brownish staining
    2. Damp / rotting floors or skirting boards
    3. White fluffy deposits on walls
2. Penetrative damp
  1. Refers to any moisture sourced outside the habitable space
  2. Occurs through roofs, chimneys, parapet walls and walls above ground level
  3. Physical mechanisms enabling water to enter fabric (Causes)
    1. Gravity
    2. Lateral winds
    3. Surface tension
    4. Higher external pressure
  4. Examples
    1. Leaks in rainwater goods
    2. Rain splash to base of walls
    3. 2 more examples
  5. Characteristics
    1. Requires link from outside to inside
    2. Needs time to percolate into building
    3. Can by mistaken for rising damp
    4. Carries sulphates and carbonates
3. Condensation
  1. 2 main types
    1. Surface
    2. Interstitial
  2. Moisture caused by everyday living.
    1. Occurs when warm moist air comes into contact with a cold surface which is lower in temperature.
  3. Factors that contribute (Causes)
    1. Temperature
    2. Ventilation rate
    3. Amount of moisture available
  4. Examples
    1. Build up of condensation on glazing panes, can lead to rotting of window cill
    2. Black mould in crescent shape formation
  5. Characteristics
    1. Can be mistaken for rising damp
    2. Needs cold surfaces to form water
    3. Does not contain contaminants
    4. Can form inside walls and roofs
    5. Causes mould marks in still areas
CORROSION
1. Causes
  1. Carbonation
    1. CO2 in atmosphere reacts with cement hydrates to form Calcium Carbonate
      1. Lowers alkalinity of concrete, which leads to depassivation of steel reinforcement
  2. Chloride action
    1. Cast in chlorides
      1. Up until 1977, CaCl routinely added to concrete as an accelerator
    2. De-icing salts
      1. Salt spreading on pedestrian areas
      2. Salts brought in by cars
    3. Marine environment
2. Effects
  1. Carbonation
    1. Uniform corrosion
    2. Hairline cracking along line of reinforcement
  2. Chloride action
    1. Localised, severe pitting corrosion
    2. Bulging / cracking of concrete
    3. Rust staining
STRUCTURAL MOVEMENT
1. Subsidence
  1. Vertical downward movement of a building
    1. Loss of support beneath foundations
  2. Causes
    1. Clay soils
    2. Trees
    3. Leaking drains
    4. Mining activity
  3. Effects / signs
    1. Distortion of openings
    2. Stepped cracking
    3. Cracks extending through DPC
    4. Cracks mirrored internally
    5. Seasonal opening and closing of cracks
2. Settlement
  1. Usually occurs in new or relatively new buildings.
  2. Cause
    1. Initial
      1. Ground compacting beneath building, adjusting to new load
    2. Long term consolidation
      1. Water table variation
      2. Load variation
  3. Effects / signs
    1. Same as subsidence
3. Moisture movement
  1. Causes
    1. Irreversible
      1. Once-off change in baseline moisture content
      2. Bricks : period of moisture absorption as they adjust from post-firing dryness
      3. Concrete : undergoes shrinkage during initial drying out
    2. Reversible
      1. Direct wetting / drying
  2. Effects / signs
    1. Bulging / distortion
    2. Tensile cracks
  3. Affects traditional, permeable materials
4. Thermal movement
  1. Causes
    1. Seasonal and diurnal patterns
      1. May produce permanent movement
  2. Effects / signs
    1. Cracking
    2. Blistering
    3. Displaced movement
  3. Reversible process
  4. Factors affecting failure
    1. Rate of temperature change
    2. Differential movement between components
    3. Thermal capacity of component

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BUILDING PATHOLOGY : COMMON DEFECTS (PART 1)

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