Fibre-cement cladding – bubbling or blistering 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

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

Listed under: Exterior, fibre-cement, cladding, walls, fibre-cement cladding

Cause

Loss of adhesion due to excess moisture in substrate

Repair

  • first, address the moisture problems in the fibre-cement. This may mean, for example, fixing broken gutters above the cladding or removing vegetation close to the building to allow more air movement

  • if the cladding itself remains weathertight and in good condition, gently scrape and/or sand off loose paint and clean away any dust. Allow the cladding to dry thoroughly and then seal bare material. Paint the clean, dry surface with a minimum two coats of good quality semi-gloss or high gloss acrylic paint

  • if you suspect there may be leaks through the cladding – more likely where the fibre-cement has a texture-coated finish and/or a flush-finish (giving the ‘monolithic’ look) and dates from around the mid 1990s to the mid/late 2000s – engage an experienced New Zealand Institute of Building Surveyors (NZIBS) building surveyor to look at the building

  • if the fibre-cement is many decades old, there is a possibility that it may contain asbestos. This requires greater care to ensure that work does not result in asbestos fibres becoming airborne after scraping or sanding. If you are not sure, you can get a small piece (about the size of two $2 coins, or approximately 2 x 3 cm) tested at one of the labs listed on our asbestos page

  • once the cladding has been repaired, inspect it at least once a year and ensure that the coating and joints remain in good condition

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Cause

Poor initial substrate preparation

Repair

  • see first repair above

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Cause

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

Repair

  • see first repair above
  • oil-based paint should generally not be applied over water-based paint or on fibre-cement
  • if you are unsure whether the paint on a cladding is oil-based or water-based, soak one end of a white rag or cotton wool ball with a solvent such as acetone-based nail polish remover. Rub the painted surface vigorously. If the paint marks the rag, then it is water-based
  • remove as much of the oil-based paint as possible before cleaning and repainting

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Cause

Surface was damp or dirty when painted previously

Repair

  • see first repair above

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Cause

Dark colours increasing surface temperatures

Repair

  • see first repair above
  • darker colours absorb more heat from the sun, resulting in the paint and substrate expanding and shrinking with temperature changes, reducing the lifespan of the paint. Repaint using a lighter colour

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Cause

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

Repair

  • see first repair above

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