Plywood cladding – paint failure at base of walls

Causes

Cladding covered by soil/foliage

The back surface of boards too close to the ground, not sealed and absorbing moisture

Concrete has been placed up to and against cladding

High subfloor moisture levels behind the cladding

Bottom of cladding too close to waterproof deck surface, apron flashing and absorbing moisture 

Listed under: Exterior, timber and wood-based, plywood, Subfloor, cladding, decks, flashings, walls, moisture, durability, rot, leaks, wall cladding, plywood sheets or planks

Cause

Cladding covered by soil/foliage

Repair

  • cut back foliage and replace any plants that are likely to regrow and cause the problem to return

  • lower the soil level to be well clear of the cladding – the bottom of the plywood must be able to dry completely. As a guide, the gap required in new construction with plywood cladding is 100 mm above a paved surface or 175 mm above a finished unpaved surface. Aim for this wherever possible, but even a gap less than this could reduce the risk of moisture uptake and allow the cladding to dry

  • check for damage to the plywood. Where plywood is damaged, replace it with H3 LOSP-treated ply with a 3-coat paint finish or H3 CCA-treated material

  • where framing behind the cladding is damaged (unless it is limited to a small area of timber), engage a registered building surveyor to advise on the cause, extent and repair options

  • where the plywood is sound, allow it to dry out completely. Scrape off loose paint and sand until the surface is sound. Seal the plywood – especially the edges – and repaint.

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Cause

The back surface of boards too close to the ground, not sealed and absorbing moisture

Repair

  • lower the soil level to be well clear of the cladding – the bottom of the cladding must be able to dry completely

  • check for damage to the plywood. Where plywood is damaged, replace it with H3 LOSP-treated ply with a 3-coat paint finish or H3 CCA-treated material

  • where framing behind the cladding is damaged (unless it is limited to a small area of timber), engage a registered building surveyor to advise on the cause, extent and repair options

  • where the plywood is sound, allow it to dry out completely. Scrape off loose paint and sand until the surface is sound. Seal the plywood – especially the edges – and repaint.

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Cause

Concrete has been placed up to and against cladding

Repair

  • break up and remove concrete or paving. Reform the ground surface so rainwater will flow away from the building

  • check for damage to the plywood. Where plywood is damaged, replace it with H3 LOSP-treated ply with a 3-coat paint finish or H3 CCA-treated material, ensuring the base of the new cladding is well clear of the ground

  • where framing behind the cladding is damaged (unless it is limited to a small area of timber), engage a registered building surveyor to advise on the cause, extent and repair options

  • where the plywood is sound, allow it to dry out completely. Scrape off loose paint and sand until the surface is sound. Seal the plywood – especially the edges – and repaint.

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Cause

High subfloor moisture levels behind the cladding

Repair

  • reduce subfloor moisture levels:

    • if there is a leak under the house, identify the source and location. Make a permanent repair, or call a licensed or certifying plumber (work on waste pipes must by law be carried out by a licensed or certifying plumber)

    • if surface water is running under the house, divert it away by lowering the ground levels around the building and sloping the ground away from the house

    • clear away obstructions around the house perimeter such as planting or soil build-up outside the vents

    • for painted vents or grilles, remove paint build-up that may reduce the air path space

    • clear away items stored under the house to improve air flow

    • ensure there is not less than 3500 mm² of clear open subfloor venting (grilles or gaps between baseboards) for every 1 m² of floor area

    • make ventilation openings high in the subfloor space, near to the underside of bearers

    • spread vents evenly around the building perimeter to allow cross-ventilation.

  • check for damage to the plywood. Where plywood is damaged, replace it with H3 LOSP-treated ply with a 3-coat paint finish or H3 CCA-treated material, ensuring the base of the new cladding is well clear of the ground

  • where framing behind the cladding is damaged (unless it is limited to a small area of timber), engage a registered building surveyor to advise on the cause, extent and repair options

  • where the plywood is sound, allow it to dry out completely. Scrape off loose paint and sand until the surface is sound. Seal the plywood – especially the edges – and repaint.

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Cause

Bottom of cladding too close to waterproof deck surface, apron flashing and absorbing moisture 

Repair

  • check for damage to the plywood. Where plywood is damaged, replace it with H3 LOSP-treated ply with a 3-coat paint finish or H3 CCA-treated material, ensuring the base of the new cladding is well clear of the ground

  • where framing behind the cladding is damaged (unless it is limited to a small area of timber), engage a registered building surveyor to advise on the cause, extent and repair options

  • where the plywood is sound, allow it to dry out completely. Scrape off loose paint and sand until the surface is sound. Seal the plywood – especially the edges – and repaint.

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