Timber trims – bubbling or blistering of paint

Causes

Loss of adhesion due to excess moisture in substrate

Poor initial substrate preparation

Oil-based (alkyd) paint applied over water-based (latex) paint

Surface was damp or dirty when painted previously

Dark colours increasing surface temperatures 

Timber swelling/shrinkage caused by moisture absorption into timber end grain if joints were not adequately primed before installation

Water-based paint coat exposed to moisture before paint has fully dried

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

Cause

Loss of adhesion due to excess moisture in substrate

Repair

  • scrape and/or sand off loose paint; sand bare timber until surface is sound; prime; fill joints with putty or exterior grade flexible (polyester) filler; paint with a minimum two coats of semi-gloss or high gloss acrylic paint
  • if blistering goes through to the substrate, it indicates that there is a high moisture content in the timber and this must be addressed before repainting
  • 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

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Cause

Poor initial substrate preparation

Repair

  • scrape and/or sand off loose paint; sand bare timber until surface is sound; prime; fill joints with putty or exterior grade flexible (polyester) filler; paint with a minimum two coats of semi-gloss or high gloss acrylic paint
  • if blistering goes through to the substrate, it indicates that there is a high moisture content in the timber and this must be addressed before repainting
  • 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

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Cause

Oil-based (alkyd) paint applied over water-based (latex) paint

Repair

  • oil-based paint should generally not be applied over water-based paint. To determine whether an existing paint finish is water-based or solvent-based:

    • soak a cotton ball in rubbing alcohol (isopropyl or ethyl alcohol), an acetone-based nail polish remover or lacquer thinner

    • rub it over a small, inconspicuous section of the trim

    • if paint comes off, it is water-based; if unaffected, it is a solvent-based paint

  • remove existing paint and sand bare timber until surface is sound. Ensure timber is thoroughly clean and dry, then prime. Fill joints with putty or exterior grade flexible (polyester) filler. Paint with a minimum two coats of semi-gloss or high gloss acrylic paint

  • 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

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Cause

Surface was damp or dirty when painted previously

Repair

  • scrape and/or sand off loose paint; sand bare timber until surface is sound; prime; fill joints with putty or exterior grade flexible (polyester) filler; paint with a minimum two coats of semi-gloss or high gloss acrylic paint
  • if blistering goes through to the substrate, it indicates that there is a high moisture content in the timber and this must be addressed before repainting
  • 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

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Cause

Dark colours increasing surface temperatures 

Repair

  • scrape and/or sand off loose paint. Sand bare timber until surface is sound, then prime. Fill joints with putty or exterior grade flexible (polyester) filler. Paint with a minimum two coats of semi-gloss or high gloss acrylic paint

  • select paint of a lighter colour where possible – darker colours attract heat, which can cause greater expansion/contraction of the timber, and thus a reduced lifespan for the paintwork

  • if blistering goes through to the substrate, it indicates that there is a high moisture content in the timber and this must be addressed before repainting

  • 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

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Cause

Timber swelling/shrinkage caused by moisture absorption into timber end grain if joints were not adequately primed before installation

Repair

  • scrape and/or sand off loose paint; sand bare timber until surface is sound; prime; fill joints with putty or exterior grade flexible (polyester) filler; paint with a minimum two coats of semi-gloss or high gloss acrylic paint
  • if blistering goes through to the substrate, it indicates that there is a high moisture content in the timber and this must be addressed before repainting
  • 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

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Cause

Water-based paint coat exposed to moisture before paint has fully dried

Repair

  • scrape and/or sand off loose paint; sand bare timber until surface is sound; prime; fill joints with putty or exterior grade flexible (polyester) filler; paint with a minimum two coats of semi-gloss or high gloss acrylic paint
  • if blistering goes through to the substrate, it indicates that there is a high moisture content in the timber and this must be addressed before repainting
  • 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

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