Bitumen-impregnated cladding – deterioration of factory finish

With one particular product imported from the 1990s to the mid 2000s, there have been cases where the bitumen coating has been found to break down, leading to water reaching the cellulose fibres inside the material and subsequent product failure. If you have bitumen-impregnated roof or wall cladding that was installed in this period, we recommend you inspect it closely at least once a year.

 

Causes

Surface degradation due to age or weathering

Listed under: Exterior, cladding, walls, wall cladding, bitumen-impregnated corrugated fibre

Cause

Surface degradation due to age or weathering

Repair

  • determine the extent of the degradation – if very minor, several coats of good quality acrylic paint may be sufficient, but consult the cladding supplier for their advice first. Do not use solvent-based paint
  • if degradation is severe, the cladding may need to be replaced. If the extent of damage is not clear, engage a building surveyor for their opinion
  • under the Building Code, claddings are required to be durable for not less than 15 years. If weathering has resulted in premature failure, contact the supplier
  • if the cladding is at the end of its serviceable life, it should be replaced. If it has performed satisfactorily for over 15 years, it can be replaced with a comparable lightweight cladding material without a building consent
  • if the cladding was installed less than 15 years ago, or it will be replaced with a very different type of material, replacing it will require a building consent
  • where it is suspected that the building may have been leaking and there is a risk of damage to framing timber, engage a building surveyor for advice 

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