BUILDING PATHOLOGY : COMMON DEFECTS (PART 1)

BUILDING PATHOLOGY : COMMON DEFECTS (PART 1)

1. TIMBER DEFECTS

   • Beetle rot
   • Dry / wet rot
     • Causes
       • Species of timber
       • Chronic dampness
       • Poor ventilation
       • Normal internal temperature
     • Effects / signs
       • Sound hollow and dull
       • Be of abnormal colour
       • Wood disintegration
       • Fungi
         • Dry rot
           • Brown
           • Cubical
           • Fluffy
           • Yellow mycelium
           • Musty smell
           • Will not grow in saturated conditions
           • Red spores
         • 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

2. DAMP

   • Rising damp
     • Moisture present in ground below walls rising up through fabric of wall
       • Capillary action
     • Below ground moisture sources
       • Free water in subsoil (water table)
       • Water main breach
       • Build up from drain / pipe leaks
     • Investigation using trial holes
       • Confirm existence of DPC which may be concealed
       • Verify construction of walls below ground
       • Establish height of water table
     • Chemical analysis
       • Can confirm that salts present could only have been derived from below ground sources.
     • Causes
       • Defective DPC
       • DPC bridging
       • No DPC
     • Characteristics
       • 'Tide line' of yellow / brownish staining
       • Damp / rotting floors or skirting boards
       • White fluffy deposits on walls
   • Penetrative damp
     • Refers to any moisture sourced outside the habitable space
     • Occurs through roofs, chimneys, parapet walls and walls above ground level
     • Physical mechanisms enabling water to enter fabric (Causes)
       • Gravity
       • Lateral winds
       • Surface tension
       • Higher external pressure
     • Examples
       • Leaks in rainwater goods
       • Rain splash to base of walls
       • 2 more examples
     • Characteristics
       • Requires link from outside to inside
       • Needs time to percolate into building
       • Can by mistaken for rising damp
       • Carries sulphates and carbonates
   • Condensation
     • 2 main types
       • Surface
       • Interstitial
     • Moisture caused by everyday living.
       • Occurs when warm moist air comes into contact with a cold surface which is lower in temperature.
     • Factors that contribute (Causes)
       • Temperature
       • Ventilation rate
       • Amount of moisture available
     • Examples
       • Build up of condensation on glazing panes, can lead to rotting of window cill
       • Black mould in crescent shape formation
     • Characteristics
       • Can be mistaken for rising damp
       • Needs cold surfaces to form water
       • Does not contain contaminants
       • Can form inside walls and roofs
       • Causes mould marks in still areas

3. CORROSION

   • Causes
     • Carbonation
       • CO2 in atmosphere reacts with cement hydrates to form Calcium Carbonate
         • Lowers alkalinity of concrete, which leads to depassivation of steel reinforcement
     • Chloride action
       • Cast in chlorides
         • Up until 1977, CaCl routinely added to concrete as an accelerator
       • De-icing salts
         • Salt spreading on pedestrian areas
         • Salts brought in by cars
       • Marine environment
   • Effects
     • Carbonation
       • Uniform corrosion
       • Hairline cracking along line of reinforcement
     • Chloride action
       • Localised, severe pitting corrosion
       • Bulging / cracking of concrete
       • Rust staining

4. STRUCTURAL MOVEMENT

   • Subsidence
     • Vertical downward movement of a building
       • Loss of support beneath foundations
     • Causes
       • Clay soils
       • Trees
       • Leaking drains
       • Mining activity
     • Effects / signs
       • Distortion of openings
       • Stepped cracking
       • Cracks extending through DPC
       • Cracks mirrored internally
       • Seasonal opening and closing of cracks
   • Settlement
     • Usually occurs in new or relatively new buildings.
     • Cause
       • Initial
         • Ground compacting beneath building, adjusting to new load
       • Long term consolidation
         • Water table variation
         • Load variation
     • Effects / signs
       • Same as subsidence
   • Moisture movement
     • Causes
       • Irreversible
         • Once-off change in baseline moisture content
         • Bricks : period of moisture absorption as they adjust from post-firing dryness
         • Concrete : undergoes shrinkage during initial drying out
       • Reversible
         • Direct wetting / drying
     • Effects / signs
       • Bulging / distortion
       • Tensile cracks
     • Affects traditional, permeable materials
   • Thermal movement
     • Causes
       • Seasonal and diurnal patterns
         • May produce permanent movement
     • Effects / signs
       • Cracking
       • Blistering
       • Displaced movement
     • Reversible process
     • Factors affecting failure
       • Rate of temperature change
       • Differential movement between components
       • Thermal capacity of component

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