Blistering

Bubbles resulting from localised loss of adhesion and lifting of the paint film from the underlying surface.

Possible Cause

• Painting a warm surface in direct sunlight.
• Application of an oil-based or alkyd paint over a damp or wet surface.
• Moisture escaping through the exterior walls (less likely with latex paint than with oil-based or alkyd paint).
• Exposure of latex paint film to dew, high humidity or rain shortly after paint has dried, especially if there was inadequate surface preparation.

Solution

If blisters go down to the substrate, first try to remove the source of moisture. Remove blisters by scraping, then sanding the surface.

Prime any bare timber with a high quality water-based primer, and repaint with a high quality water-based exterior paint. 

Images courtesy of the Paint Quality Institute from Dow Coating Materials