A Perfect Paint Job
Spring is a great time to repaint, says Mark T. Knaebe, a chemist at the Forest Products Laboratory in Madison, Wisconsin. "I like it because you can be fairly sure you'll finish the job before it gets too cold." As co-author of "Finishes for Exterior Wood," a book summarizing the lab's 75 years of paint research, Knaebe knows a quality job takes time. He recommends starting with a quick test to determine the extent of the work. First, choose an inconspicuous place where the paint is worst. Clean the surface, let it dry and paint a small patch. The next day, press on a Band-Aid and then quickly pull it off. If the tape is clean, it's safe to repaint after scrubbing the whole house. If the tape pulls off all the paint down to bare wood, the house needs to be stripped before it's repainted. If just new paint comes off, the old paint is too chalky and you'll have to coat the whole house with an oil primer first. For houses with some flaking but not enough to require stripping, remove loose paint with a scraper and a power washer, taking appropriate precautions if you suspect the old paint contains lead. Sand all bare wood and exposed paint edges or the new paint will be thin there and will chip in no time. Scrub the walls with water and kill any mildew by using a solution of one par household bleach to three parts water. Rinse and let the wood dry.
Most painters would simply prime and then paint at this point, but Knaebe recommends coating bare spots with a water-repellent preservative specifically labeled as compatible with paint. The repellent will limit shrinking and swelling of the siding due to moisture. Three sunny days later, you can prime the bare spots or coat the whole house. (If you've stripped all the paint, latex primer is recommended.) Apply the finish coat soon. Soap-like compounds can form on oil primers in as little as two weeks. If there is a longer delay, scrub and rinse before applying the top coat. Two coats will probably be needed with latex, Knaebe says. Before painting, check the air temperature and the weather forecast and make sure they're compatible with the weather guidelines on the label. Weather that is too hot, too cold, too humid or too windy can undermine the best prep work.
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