Blistering Paint
Causes and Solutions

A condition called blistering can occur to newly applied paint as well as existing finishes. This problem typically happens to Acrylic and Latex finishes, but it is possible with Alkyd, or oil base, finishes. Bubbled paint can occur indoors or out and often you won’t know if it can happen until it happens.

The only way to prevent this condition is to understand why it occurs and use good sound painting practices.

Typical Causes of Blistering Paint and Treatment

There are several primary reasons why paint would bubble or blister. Plus there are some differences between blistered paint and bubbled paint.

A blister is usually the loss of adhesion between the new and old layers. This usually forms after the paint has dried, the amount of time could be a day or even a year or more.

On the other hand, a bubble is usually caused by a chemical reaction. This bubble can be formed by expanding vapors or excess moisture on the surface during application. A paint bubble usually forms before or during the initial drying phase.

Warm or Hot Surface

If a wall is in direct sunlight chances are it will be quite warm and possibly hot to the touch. When any paint is applied to a hot surface the solvents, water for latex and mineral spirits for oil base, vaporize very quickly. At the same time, the paint is drying, forming a film and becoming resistant to the transfer of the solvent underneath. This creates a bubble. Excessive thinning combined with heat will increase the chances of this condition occurring.

Solution – Avoid painting in direct sunlight or application to hot surfaces. Paint conditioners such as Flotrol, for water base paints, or Penitrol, for oil base paint, can be used to slow down the drying of paint when applied in hot weather. These paint conditioners are better than water or mineral spirits as they have slower evaporation rates.

Wet or Damp Surface

Wet substrates such as wood or concrete block, can cause this condition and eventual peeling. This is especially true for oil base paint. Water underneath the paint film can cause a lack of adhesion that can occur across a large area or be localized.

Solution – Allow the surface to dry completely before priming and painting. If the moisture persists you will need to track down its source and repair the problem before painting.

Rain, Dew and High Humidity

Exposure of the paint film to rain, dew or high humidity shortly after application and during the drying phase can cause paint blisters, sometimes full of water.

Solution – Allow 4 or more hours of drying before predicted adverse weather. Often this condition will disappear if dry conditions quickly return. If not, removing the bubbled paint and repainting the affected area is needed.

Lifting Old Layers of Paint

It is also possible for a large blister or paint bubble to form a few days after painting, apparently for no good reason. These occurrences are usually caused when the new paint film dries and shrinks, pulling on the underlying layers and lifting them from the surface.

Homes that originally were stained or treated with linseed oil then painted with latex or acrylic paint without a primer can show this lifting of a paint layer when a new layer is added. The same thing can happen when a home is originally painted with an oil base.

This is unfortunate as the older layers are not fully adhered. In this case the only prevention is the original preparation or lack of. Repairing the affected areas as the damage occurs is all that can be done.

Fixing Blistering Paint

Removing blistering paint involves hand scraping and sanding to blend in the paint edges with the surrounding surface. For large areas power sanding alone can be used. Affected wood surfaces could require extensive sanding, including down to raw wood.

For masonry, a good alternative to hand scraping is pressure washing. Careful use of a pressure washer will remove many paint blisters, but it is still advisable to go over the surface with a hand scraper.

As you are removing the affected areas, determine if it was caused by moisture or heat. To determine this, observe if there is paint or raw wood underneath. Raw wood indicates a moisture problem and finding paint indicates a problem with heat.

If moisture is the problem, determine its source and repair where needed to prevent any more moisture from affecting your paint job.

There’s numerous ways that water can reach a painted surface.

• Missing or cracked caulking around windows and doors or missing from gaps between the siding.
• Clogged gutters can cause excess moisture under singles.
• Inadequate attic ventilation.
• Persistent dampness in a basement.
• Vegetation to close to the house. Not enough fresh air movement around the house.

In all instances, it is advisable to use a good appropriate primer over the affected area. Allow the necessary time for the primer to fully dry, this could take a day or two depending on the type used.

With the necessary repairs made, blistering paint removed, affected area(s) primed and all gaps caulked; you can finally start to apply some paint.