Bubbles resulting from localized loss of adhesion and lifting of the paint film from the underlying surface. Possible Causes:
  1. Painting a warm surface in direct sunlight.
  2. Application of oil- base or alkyd paint over a damp or wet surface.
  3. Moisture escaping through the exterior walls.
  4. Exposure of latex paint film to dew, high humidity or rain shortly after paint has dried, especially if there was inadequate surface preparation.
  1. If blisters go down to substrate, try to remove the source of moisture.
  2. Repair loose caulking; consider installing an exhaust fan.
  3. If blisters do not go all the way down to the substrate, remove them by scraping, sanding; prime bare wood and repaint.