What causes exterior paint to bubble?

Written by klaire brown
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What causes exterior paint to bubble?
Apply a smooth coat of paint. (paint roller image by Ana de Sousa from Fotolia.com)

Painting can sometimes be a daunting task. Although changing the appearance of your home initially seems like a great idea, some problems may occur. It is important to understand what some of the common setbacks may be and how to prevent them, or how to repair them before you even begin to paint.

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Causes of Paint Bubbles

One of the more common failures of exterior painting is blistering, which is a bubbling of the top layer of paint. Although it can possibly occur with a latex paint, according to an extension forester for wood products at the University of Iowa, "it is most common when using oil-based paints." There are two reasons why bubbles appear, the first of which involves the temperature.

Painting in direct sunlight or on a hot surface entraps vapours as the paint dries too fast. These vapours expand, causing small- to medium-sized bubbles under the top layer of paint. Because darker colours absorb more heat, you are less likely to experience this problem with lighter colour tones.

Another cause of paint bubbles is moisture coming from inside or outside. Unlike the bubbles associated with heat, moisture bubbles penetrate through all layers of paint, into the surface. The moisture becomes trapped, thus expanding the paint film. Inside moisture is due to leaks from the house, perhaps because of plumbing problems. Outside moisture can come from precipitation. The bubbles may appear within a few hours or may take as long as a few days to pop up.

Preventing Paint Bubbles

Blistering can be prevented by taking a few cautionary steps. To avoid temperature bubbling, try to use lighter-coloured latex paint, or if you are using a darker paint, do your work during cooler times of the day.

Averting moisture blisters may require a little more work, especially when painting in the vicinity of kitchens and bathrooms. According to www.bobvila.com, "improper construction techniques and lack of flashing can cause outside water to pool at joints, on window seals, frames, or on the end grain of the wood." Flashing is a piece of metal used in wall construction to keep water out. Also, make sure all cracks or holes are filled with caulk to prevent water from seeping through interior walls.

Repairing Paint Bubbles

Once the bubbles have been discovered, allow the paint to dry completely before attempting to repair the area. It's important to determine the depth of the blisters, as there may be underlying indoor moisture complications. In addition to repairing the paint, the moisture problem needs to be addressed.

Begin by scraping and sanding the area, plus the surrounding area about 12 inches on each side, so that all paint layers are removed, then prime the area. During a cooler time of day, out of direct sunlight, apply a latex paint to cover the area.

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