Blistering or bubbling paint is a common problem that occurs on both interior and exterior painting projects. Bubbles can appear either immediately after paint has dried, or a long time afterwords.

In either case, the problem can be fixed, but certain steps must be taken before starting your project or the problem will occur again.

What causes paint to blister?

Blistering (or bubbling) paint usually occurs due to 1. Moisture or 2. Heat. Blistering due to heat usually occurs outside in direct sunlight if a surface is painted that is too warm, especially with dark colors, as they trap larger amounts of heat.

Blistering due to moisture commonly occurs inside in damp areas such as bathrooms or basements. It can occur outside as well if, for example, a surface was painted on a humid day or dewy morning.

Fixing blistering paint

First you want to determine what caused the blistering. Pull off one of the blisters. If the substrate shows, the blistering was likely caused by moisture. If it goes down to the primer or the previous coat of paint, it was likely caused by heat.

In either case all blisters should be removed by scraping or sanding. If the blistering was caused by heat, you can simply scrape and then repaint either out of the direct sunlight or in cooler temperatures. If exterior moisture was the culprit, you'll want to wait for dryer conditions.

If blistering due to moisture has occurred inside, the moisture issue will need to be addressed before painting. In bathrooms, for example, check your ventilation and install vents or exhaust fans if necessary. In basements check for cracks in the foundation or walls where moisture can come through. Sand and scrape the blistering paint to the bare substrate, then prime and paint again.