It can be caused by any of the following:

• Seepage of moisture through uncaulked joints, worn our caulk or leaks in the roof or walls

• Excess moisture escaping through exterior walls (this is more likely if paint used is solvent-based)

• Inadequate surface preparation

• Use of inferior quality paint

• Applying a solvent-based paint over a wet surface

• Previous blistering of paint (see Blistering)

First, try to identify and eliminate the cause of moisture (see Efflorescence and Mottling). Then, prepare the surface by removing all loose paint with scraper or wire brush. Sand rough surfaces and prepare surface as per label instructions prior to painting.