Blistering
 

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

Possible Cause:
Painting a warm surface in direct sunlight.
Application of oil-based or alkyd paint over a damp or wet surface.

Excessive moisture escaping from the interior of the house through the exterior walls (less likely with latex paint than with oil-based paint).

Exposure of latex paint film to dew, high humidity or rain shortly after paint has dried, especially if there was inadequate surface preparation.

Damp basements.

Painting over a surface damp with rain, dew or residual from power washing.

Solution:
If blisters go down to the substrate, try to remove the source of moisture. Repair loose caulking; consider installing an exhaust fan.
If blisters do not go all the way down to the substrate, remove them by scraping, then sanding. Next prime any bare wood and repaint with a quality exterior paint.

Recommended System:
Primer
1 Coat of FLEX BON #169 Series Exterior Alkyd Primer or
FLEX BON #194 Series Exterior 100% Acrylic Latex Primer
Topcoat
2 Coats of Top Quality FLEX BON Exterior Latex Paint