Cupping of timber weatherboards

Causes

Thermal expansion and contraction of timber

Swelling/shrinkage due to moisture absorption 

Insufficient gap left between rusticated or rebated weatherboards during installation 

Common

Listed under: Exterior, finishes, timber and wood-based, paint, timber, cladding, walls, moisture, wall cladding, painted timber weatherboards

Cause

Thermal expansion and contraction of timber

Repair

  • if the cupping is minor and no water is getting behind the cladding the boards may be left
  • if the boards have been finished with a clear coating or stain, the finish should be re-applied (confirm the weatherboards are not damaged before re-applying finish)
  • for uncoated timber, apply a clear finish, paint or stain to reduce moisture absorption
  • apply a paint or stain finish to weatherboards:
    • paint – re-apply every 7–10 years
    • stain – re-apply every 2–4 years.
  • before applying a finish, the weathered timber must be sanded back to sound timber to ensure the coating will adhere to the timber. Caution: old layers of paint may contain lead. Lead can be a health hazard if fumes, dust or paint fragments are swallowed or breathed in. For more information see Health and safety: lead-based paint
  • where water entry is possible through open laps or joints, replace affected boards
  • when replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound

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Cause

Swelling/shrinkage due to moisture absorption 

Repair

  • if the cupping is minor and no water is getting behind the cladding the boards may be left
  • if the boards have been finished with a clear coating or stain, the finish should be re-applied (confirm the weatherboards are not damaged before re-applying finish)
  • for uncoated timber, apply a clear finish, paint or stain to reduce moisture absorption
  • apply a paint or stain finish to weatherboards:
    • paint – re-apply every 7–10 years
    • stain – re-apply every 2–4 years.
  • before applying a finish, the weathered timber must be sanded back to sound timber to ensure the coating will adhere to the timber. Caution: old layers of paint may contain lead. Lead can be a health hazard if fumes, dust or paint fragments are swallowed or breathed in. For more information see Health and safety: lead-based paint
  • where water entry is possible through open laps or joints, replace affected boards
  • when replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound

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Cause

Insufficient gap left between rusticated or rebated weatherboards during installation 

Repair

  • if the cupping is minor and no water is getting behind the cladding the boards may be left
  • if the boards have been finished with a clear coating or stain, the finish should be re-applied (confirm the weatherboards are not damaged before re-applying finish)
  • for uncoated timber, apply a clear finish, paint or stain to reduce moisture absorption
  • apply a paint or stain finish weatherboards:
    • paint – re-apply every 7–10 years
    • stain – re-apply every 2–4 years.
  • before applying a finish, the weathered timber must be sanded back to sound timber to ensure the coating will adhere to the timber. Caution: old layers of paint may contain lead. Lead can be a health hazard if fumes, dust or paint fragments are swallowed or breathed in. For more information see Health and safety: lead-based paint
  • where water entry is possible through open laps or joints, replace affected boards
  • when replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound

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