Rot in stained or clear-finished timber weatherboards

Causes

Coating failure

Timber is or has been continuously damp

Inadequately treated timber – radiata pine must be treated to H3.2 if stained or clear finished stained

Non-durable or untreated timber used – timbers such as cedar and heart macrocarpa may be untreated but they must not be continuously wet in use

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

Cause

Coating failure

Repair

  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are sealed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • seal the backs of the boards
    • fill joints with putty or exterior grade flexible (polyester) filler
    • apply stain or paint in accordance with the manufacturer’s instructions
  • before replacing boards, check that the wall underlay (building paper) and framing behind weatherboards are sound
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding engage an experienced building surveyor to report on the building 

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Cause

Timber is or has been continuously damp

Repair

  • determine and address cause of continuous dampness of timber if possible. See 'Cladding in contact with the ground'
  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are sealed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • seal the backs of the boards
    • fill joints with putty or exterior grade flexible (polyester) filler
    • apply stain or paint in accordance with the manufacturer’s instructions
  • before replacing boards, check that the wall underlay (building paper) and framing behind weatherboards are sound
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding engage an experienced building surveyor to report on the building 

Back to top

Cause

Inadequately treated timber – radiata pine must be treated to H3.2 if stained or clear finished stained

Repair

  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are sealed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • seal the backs of the boards
    • fill joints with putty or exterior grade flexible (polyester) filler
    • apply stain or paint in accordance with the manufacturer’s instructions
  • before replacing boards, check that the wall underlay (building paper) and framing behind weatherboards are sound
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding engage an experienced building surveyor to report on the building 

Back to top

Cause

Non-durable or untreated timber used – timbers such as cedar and heart macrocarpa may be untreated but they must not be continuously wet in use

Repair

  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are sealed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • seal the backs of the boards
    • fill joints with putty or exterior grade flexible (polyester) filler
    • apply stain or paint in accordance with the manufacturer’s instructions
  • before replacing boards, check that the wall underlay (building paper) and framing behind weatherboards are sound
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding engage an experienced building surveyor to report on the building 

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