Blistering is caused by heat and humidity interacting with the paint.
Interior paint is often easier to apply than outdoor paint, and does not need to withstand the same type of weathering conditions, but it can encounter problems, too. Improperly applied paint, or paint that is exposed to unfavorable conditions, can be subject to blistering. Fixing these blisters takes a little work, but prevention is easier if you can find and deal with sources of humidity and moisture.
Blistering
Blisters are small places in the paint where the paint layer has lost adhesion with the surface beneath it and formed a small space of air, bubbling up or warping out of shape. Blisters form most often in acrylic and latex paints, but can be found in nearly any type of paint and can form only a day after application, or up to a year later.
Causes
Humidity is one of the most common causes of blisters and bubbles in interior paint. High humidity can cause moisture to seep into wood and indoor concrete, causing a lack of adhesion where it contacts the paint. If the humidity is high right after painting, the problem may become even worse.
Paint Drying
As the paint begins to dry, high humidity in the air will usually interact with the paint and pull sections that are not dry away from layers that have already dried, forming bubbles not only of air but of water, which can be even more damaging to the paint. Rain and dew have an even worse effect, but interior paint is only in danger of the humidity outside air can bring indoors.
Heat
If the humidity is accompanied by heat, this can worsen problems caused by bubbles. The heat causes certain solvents in the paint to evaporate more quickly, while the drying parts of the paint are resistant to the transfer of the gases, creating a bubble filled with solvent gas.
Fixing
Bubbles and blisters must be removed completely. The painter can scrape or sand them off and smooth over the section where the blisters occurred. For large areas, painters can use a power sander to save time. Often, the painter will need to apply a new coat of paint over the affected area.
Caulking
In houses, humidity can leak in easily through cracks in windows, doors or vents. Painters can caulk these cracks to seal off airflow and decrease humidity inside the house, decreasing the likelihood of blisters and other paint problems at the same time.
Basements
Basements are notorious for humidity and blister problems, since moisture can easily rise through the surrounding soil. The floor of the basement should be sealed with a waterproof sealant to help alleviate the problem. Attics can have the same issue, but are more easily ventilated than basements.
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