How to Stop Paint From Peeling on Cedar Siding
This Old House host Kevin O'Connor taps a painting contractor for pro advice
Every spring, the paint in one section of our cedar siding bubbles and comes off in sheets, right down to the bare wood. Why is this happening? What can be done about it?
—Dan Shapiro, Hunting Valley, Ohio
According to Mario Guertin, owner of Painting in Partnership, in Palatine, Illinois, says that poor adhesion is usually caused by slapdash prep. "Paint can't adhere well to dusty, mildewed, or sun-damaged surfaces," he says. Here's the fix. "Scrape off all the peeling bits, sand the remaining paint to a feather edge with 60-grit paper, kill the mildew on the old paint with a mix of diluted bleach and dish soap, then rinse thoroughly. When the bare wood is dry, sand off the decayed layer with 80-grit paper, taking care not to dish the siding." To ensure the surface is dust-free, wipe it twice with denatured alcohol and clean rags, followed with a brushed-on coat of oil-based primer, such as Cover-Stain. "Wait about an hour, then brush on the top coat of 100 percent acrylic paint."
The next step, Guertin says, is to watch what happens next spring. If the new paint peels despite all the careful work, moisture migration is the likely culprit. "When the sun warms up the wet siding, the paint pops right off."
Solving a moisture problem is not so easy, he says, in part because it's tough to know where it's coming from. Missing or damaged flashing, a leaking roof, and water vapor from inside the house due to inadequate ventilation are some of the possible sources, and they need to be identified and fixed. Also, make sure there's no caulk or paint buildup in the seams where the clapboards overlap. If those seams are sealed, cut them open so that moisture has a way to escape without affecting the paint. Prep the siding by scraping and sanding, as above, then check the wood with a moisture meter. If it reads 15 percent or less, it's safe to repaint.
But if the peeling persists even after all those issues have been remedied, Guertin says there's only one surefire way to break the cycle of scraping and repainting: Remove the old siding and start over.
Make sure to cover the sheathing with a rainscreen, like the ones made by Benjamin Obdyke. "A rainscreen creates a gap behind the siding so that moisture can vent out the top of the wall or drain out the bottom. That allows the back of the siding to dry out if it ever does get wet," Guertin says. It's also important to use siding that's primed on both sides. "Back-priming does a great job of keeping moisture out of the wood. All cut ends should be primed too."
Guertin admits that this solution is expensive but says it greatly extends the longevity of the paint job. After you paint the new siding, it shouldn't need another coat for a decade or more.