Cupping of stained or clear-finished timber weatherboards

Causes

Thermal expansion and contraction of timber

Swelling/shrinkage due to moisture absorption 

An insufficient gap was left between rusticated weatherboards during installation where boards have been finished with a clear coating or stain 

Listed under: Exterior, finishes, clear finishes, timber and wood-based, stain, timber, cladding, walls, moisture, wall cladding, stained or clear-finished timber weatherboards

Cause

Thermal expansion and contraction of timber

Repair

  • if 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 the finish
  • for uncoated timber (such as cedar), apply a clear finish, paint or stain to reduce moisture absorption. Re-apply stain 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
  • 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 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 the finish
  • for uncoated timber (such as cedar), apply a clear finish, paint or stain to reduce moisture absorption. Re-apply stain 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
  • 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

An insufficient gap was left between rusticated weatherboards during installation where boards have been finished with a clear coating or stain 

Repair

  • if 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 the finish
  • for uncoated timber (such as cedar), apply a clear finish, paint or stain to reduce moisture absorption. Re-apply stain 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
  • 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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