What Causes Bubbles in an Interior Latex Paint Job?

Moisture

• Painting over a surface that is moist can result in blisters. Although this is not a common occurrence with latex paints, it is possible when moisture is significant enough. Typically, leaks in the plumbing system above or inside the wall are to blame, because these provide significant and constant moisture. High humidity levels in your home can also provide enough moisture to cause bubbling in latex paints, particularly if the paint is exposed to these conditions before it has had the opportunity to dry.

Thick Coatings

• Bubbles that are oblong, resembling wrinkles, occur when the paint forms a skin on the surface, preventing the paint beneath from drying properly. This usually occurs more often with oil-based paints, but it not unheard of with latex when paint is applied too thickly. The water in the paint needs access to the air in order to evaporate. When coated too thickly, the air dries only the surface, leaving moisture beneath.

Poor Wall Preparation

• Latex paint bubbles most often because of a failure to prepare the wall before application. Dirt, grease or wax must be cleaned away, using soap and water. In kitchens, use a cleaner that also has a de-greasing agent to ensure that you break up and dissolve the grease rather than spread it around. Apply primer before painting the wall to ensure there is an adequate surface for the topcoat to adhere to. Wax and grease in particular will repel the water, making it impossible for the paint to form a good solid coating.

Solutions

• For bubbles that occur due to thick coatings and that do not go down to the substrate, there is no need to repaint the entire wall. Sand the bubbled areas smooth, and repaint the problem area. Bubbles caused by moisture will likely require repainting the wall, but first, remove the source of moisture to prevent a recurrence of the problem. Fix leaks and install dehumidifiers or exhaust fans in rooms such as bathrooms or basements where constant moisture is an issue. When the source of moisture is gone, sand and clean the walls, then apply a coat of primer before repainting.