Blistering Wall Paint

Wet Surfaces

• Applying paint to a damp or wet surface or in an area that has constant high humidity is the most common cause of blistering paint. Moisture blisters affect all layers of paint down to the substrate. After appearance, blisters can dry out and collapse. Smaller ones may simply disappear, but larger ones leave rough patches. Situations that make a paint job prone to blistering include leaky roofs, damp basements, inadequate ventilation, bad plumbing, unsealed concrete or block walls, missing or damaged caulking, cracks and gaps in siding, clogged gutters and vegetation close to a building.

Temperature Blisters

• A rapid rise in temperature can lead to temperature blisters, which form only in the last coat of paint. These occur when a thin, dry skin forms on the outer layer, but the paint underneath is still wet. The wet paint changes to vapor but has no way to escape and thus forms a blister. Oil-based paints are most prone to this problem with darker colors being the most apt to exhibit blistering. Thicker paint coats are also more prone. To avoid temperature blisters, paint surfaces when rapid heating is not expected to occur, such as when outdoor air temperatures are 85 degrees Fahrenheit or higher. Direct sunlight can also cause blistering.

Proper Preparation

• One of the best ways to avoid blistering is to properly prepare the surface to be painted. Paint does not adhere well to dirt, dust and joint compound. All surfaces should be thoroughly cleaned before painting and all mold and mildew removed. Exterior surfaces should be scraped and repaired prior to painting as well. Applying primer to a surface will also help avoid blisters. Doing so, however, requires waiting a day or more before applying additional coats. For unsealed concrete, use a sealer and primer that guarantees moisture or vapor blocking. Sticking with one type of paint formula, such as latex or oil, also reduces blistering.

Repairing Blisters

• When blistering occurs, allow paint to dry for several days before removing the paint from the affected areas by scraping and sanding the surface to smooth the damage. Pressure washing can help remove paint on masonry but should be followed by scraping. A heat gun may also work on some surfaces. If blisters are moisture based, removing the source of the problem, such as poor caulking, can help avoid reblistering. Once affected areas have been treated, reapply paint.