What Causes Blisters on a House's Surface?

Heat

• One of the main causes of blisters comes when the paint suffers exposure to excessive heat soon after drying. The time frame for blisters forming ranges from a few hours to one or two days after the paint dries. Heat can can cause water vapor trapped in the paint to expand, creating a bump on the surface. Improperly preparing the surface for the paint job results in a greater chance of blistering.

Moisture

• The second major cause of blistering occurs when a source of moisture bleeds into the paint. Rain can cause blisters in some circumstances, but an undiscovered leak in the home is often the culprit. Moisture blisters usually affect all the layers of paint, not just the top coat. They also tend to dry out and deflate after forming. When the blister collapses it might disappear, leave an irregular area or start to peel.

Repair

• Repairing blisters requires scraping and sanding the blister or the rough spot left after a blister deflated. Wait a few days after the blister appears to start work. After removing the blister and smoothing the spot with sandpaper, apply a new coat of paint. If moisture has caused the bubble, then the blistering will return. To permanently repair any moisture blisters, you must find the source of the moisture and eliminate it.

Prevention

• Prevention remains the most effective way to defend your home's paint job from blisters. Check the exterior and interior of your house for any water leaking into your walls before painting. When applying paint, use the "follow the sun" method, advises Michigan State University. By painting the north side of a structure early in the morning, followed by the east, south and west sides as the day continues, you avoid having the paint exposed to excessive heat at a critical time.