Q: I have a pergola that is over a patio and covered with wisteria. It was installed in 2009 and first painted in 2010. That job lasted for three or four years with little or no peeling. But for the past two years, I've had to have it repainted each year because the paint chipped, peeled and "rained" down on the patio. Last year we used an oil-based paint. Less than a year later, very little paint remains on the wood. I need a solution that lasts at least a couple of years, but I will not pay the $3,000 estimate I just got. What do you suggest?

Washington

A: A couple of issues are probably going on here. Since the pergola was out in the weather for a year before the first coat of paint went on, there is a good chance that many of the wood fibers at the surface became weathered and were no longer well-attached to the underlying wood. The sun’s ultraviolet rays do that, which is why weathered wood should be sanded to get rid of the gray fibers before it’s painted. Regardless if that was done, the first paint coat probably stayed on because it was a uniform layer. But when it came time to repaint, there were patches of paint and patches of exposed wood, so the second coat didn’t adhere evenly. If the painter didn’t sand the surface, edges of patches from the first layer stayed sharp, allowing peeling to begin there. And if the surface wasn’t completely clean and if the wisteria had grown enough to keep the top of the pergola shaded and therefore wet for long periods, the paint would have been even more likely to peel.

Switching to an oil paint didn’t work because oil paint becomes more brittle over time than cured water-based paint, so wherever that new layer covered existing paint, the top paint cracked and started the peeling problem again.

On top of all of this is the fact that the horizontal surfaces — such as the top of your pergola — are the hardest place to keep paint from peeling. It’s why decks have traditionally been stained rather than painted. Paint can peel, but penetrating oil stains, which don’t form a surface layer, cannot. Staining your pergola isn’t an option, though, since stains work only on bare wood. Plus, most of the stains on the market — especially ones that give a white look — are water-based finishes that form a film, albeit a thin one. The look of stained wood also doesn’t give the crisp white look that you are aiming for.

So what to do now?

Jenny Burroughs, senior product manager for PPG, a paint manufacturer, says the crucial first step is excellent preparation. You’ve probably heard that from contractors you’ve consulted, but there is no way around it. Good prep gets pricey on a structure like a pergola because all of the work is overhead and every piece has at least four and sometimes six surfaces that need to be worked.

To take off loose paint, Burroughs suggests running a putty knife over the wood. A hand scraper with a sharp blade also would work. A professional might want to use a power washer.

Once all of the loose paint is off, the surface needs to be sanded, with particular attention to bare wood and the edges of remaining paint patches. Burroughs recommends using 180-grit sandpaper. Then all of the sanding dust needs to be brushed or rinsed off, and the wood needs to dry.

At last, it’s time to paint. Burroughs recommends using PPG Timeless Exterior Paint + Primer ($39.98 a gallon at Home Depot ). This is a 100 percent acrylic paint formulated for “high build,” which means it creates a slightly thicker coat than usual. That allows the paint to create a uniform surface even when the underlying surface is uneven because parts of it are bare wood while others have previous paint, Burroughs said. Other manufacturers make similar products; look for labeling that indicates similar characteristics. Although you shouldn’t use oil paint over water-based paint, the reverse is okay. But if the finish isn’t specifically labeled as paint and primer in one, you should use a primer to bridge the two types of topcoat.

Although the PPG product’s label says “complete one coat hide and coverage,” Burroughs recommends applying two coats to ensure a more durable finish. Two coats are especially important on the top surface of a pergola, she says.

On a new pergola, an extra step during construction would make a big difference in helping paint to stick, suggests Jack Mann, a technical support specialist at Jamestown Distributors (800-497-0010; jamestowndistributors.com ), a boating-supply company. “Slope the top surface so water runs off,” he says. When the framing of a pergola is flat on top, water can pool there. “It will penetrate paint film over time and will probably blister the paint,” he says. “That’s true of any paint.”

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