Exterior Paint Bubbling and Peeling — San Francisco, California

Exterior paint that bubbles, blisters, or peels in sheets off siding, trim, or fascia boards signals a moisture or adhesion failure that will continue spreading until the root cause is addressed. Two distinct failure modes look similar but have different causes. Heat blistering produces small, isolated bubbles on sun-facing walls within weeks or months of painting — the surface was painted in direct sunlight or on a surface too hot for the coating to cure properly, trapping solvent vapors under the film. Moisture blistering produces larger, more diffuse bubbles that form over time as water vapor from inside the wall (cooking, bathing, poorly vented dryer exhaust) migrates outward through the wall cavity and pushes against the paint film from behind. The blisters often contain liquid water when punctured. Full-sheet peeling, where paint lifts in large flaps or curls away from the substrate, indicates adhesion failure — typically caused by painting over chalky, dirty, or glossy surfaces without proper preparation, or by painting over moisture-saturated wood. An exterior painter can diagnose which failure mode is present by examining blister size, location, contents, and substrate condition, then strip the failed coating, address the moisture source (add bathroom exhaust venting, reroute dryer vent, install kick-out flashing), prime bare wood with a moisture-blocking primer, and repaint with a breathable acrylic-latex system rated for the climate.