It’s always a good idea to save some leftover paint. But if you don't store that paint properly, years later, when hallway walls or exterior doors need touching up in spots, you might find that the paint has deteriorated to a point that you can't use it.
Water-based latex paint (the kind that Consumer Reports tests because these easy-to-apply, easy-to-clean finishes are the most popular choice for consumers) can last for years—or go bad in mere months. “When the paint can is bulging or the lid is puffed up, that means microorganisms are eating the paint and giving off gas,” says Rico de Paz, Consumer Reports’ paint expert. “The gas generates pressure and inflates the can.” Other signs that a paint is past its prime include a thick, rubber-like film topping the paint, or when the paint doesn’t mix well when stirred or doesn't stay uniformly blended for 10 to 15 minutes after mixing.
If your paint doesn't have those problems, try it out on a piece of cardboard. You want to make sure that the paint can still be applied easily with a brush or roller, the color is uniform, and the surface is smooth and without tiny particles.
"Once you're ready to paint, use a brush or roller to blend the paint into what's already on the surface, go beyond the spot you're touching up," de Paz says. If the touched-up spot is noticeable when dry, try again. The last resort is to repaint the entire area.
What to Do With Leftover Paint
Save it. The best way to preserve paint is to store it in an airtight container to keep the water from evaporating and prevent microorganisms from getting in. You can keep it in the original can or transfer the paint to a clean jar with a screw-on lid. Keep it at room temperature. That means not storing it in the garage or shed, where temperature extremes can ruin the paint. Label leftover paint—"Charlotte and Abigail's bedroom walls, April 2017"—so that years from now you'll know where you used it.
Dispose of it. Properly dispose of unsalvageable old paint. To find out what to do where you live, check the website of your municipal or county government, or call your local department of public works. Visit Earth911 for more details on disposing of leftover paint.
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