• Seepage of moisture through uncaulked joints, worn caulk or leaks in roof or walls.
• Excess moisture escaping through the exterior walls (more likely if paint is oil-based).
• Inadequate surface preparation.
• Use of lower quality paint.
• Applying an oil-based paint over a wet surface.
• Earlier blistering of paint (see Blistering).

Try to identify and eliminate cause of moisture (see efflorescence and Mottling).
Prepare surface by removing all loose paint with scraper or wire brush, sand rough surfaces, prime bare wood. Repaint with a top quality acrylic latex exterior paint for best adhesion and water resistance.