Q: We had aluminum siding removed in late spring 2021 and found most of the wood siding underneath was good. We replaced some and had the house painted. But the paint is already peeling — mostly on the older wood, which I suspect was not properly prepared. We need to repaint. What is the best way to prepare the wood? How many coats? And do we need a primer? The house is about 1,200 square feet and has one floor with an attic. Is this a possible DIY project?
Raleigh, N.C.
A: You’re right: Inadequate preparation probably is what caused the paint to peel.
Paint can fail for numerous reasons: The surface and paint were too hot or too cold. The siding was too wet. The surface was dirty. A first coat of paint wasn’t dry before a second coat was applied. The list goes on.
When paint peels from the faces of siding boards, sometimes the cause is moisture from the interior working its way to the exterior to evaporate. The pressure of the water vapor pushes paint off the wood. If a steamy bathroom lacks ventilation, it’s sometimes possible to outline the shape of the bathroom on the exterior wall by where the paint peels.
In your case, the picture you sent shows paint peeling mostly along the lower edges of the boards and, to a lesser extent, along the ends. Paint typically begins to peel first in these areas partly because they are most prone to staying wet. Gravity carries moisture in a board to its lower edge, and the ends of boards soak up moisture because wood fibers are like straws, running lengthwise in the boards and open at the ends. But peeling paint that’s just a few years old also points to poor preparation, said a customer-service representative for paint manufacturer Sherwin-Williams. The new paint probably didn’t stick well to those areas because older paint there was already peeling, or paint there had worn away and left weathered wood as the base for new paint. Or the lower edges of the boards, which are prone to collecting dirt and harboring mildew, weren’t completely clean and dry.
So what to do now? First, fix any underlying problems. For example, if the peeling is worse on a wall with a bathroom, add a fan vented to the outdoors. Or, if it’s peeling where gutter water splashes onto the siding, channel the water farther from the house. If it’s most noticeable on the north side of the house, where the siding is in shade and doesn’t dry as quickly between storms, trim or remove shrubs and vines close to the wall.
If your house was built before 1978 and you don’t know whether the paint contains lead, either assume it does or hire a certified inspector to test for it. Homeowners who love DIY projects, are comfortable working on ladders and have the time to devote to a big project can certainly paint a house, but dealing with lead paint that’s peeling is a tipping point: Hire a contractor certified in lead-safe procedures. North Carolina, like most states, requires this certification for all contractors involved in renovation, repair and repainting.
For paint to stick to a surface where previous paint is peeling, all of the loose paint needs to be removed. “Scrape or sand whatever is willing to come off,” said the Sherwin-Williams representative. If the paint has lead, that task needs to be done in a way that keeps the worker from breathing dust and from spewing lead-laden dust into the yard or neighborhood. Some contractors invest in sanders with vacuums to capture virtually all of the dust.
The siding also needs to be clean. Some painters start by power-washing the walls, which dislodges a lot of the loose paint. However, too high a pressure can erode the wood and make it harder for new paint to stick. It also pushes a lot of water into the wood, meaning more sunny days are needed to dry the wood before repainting. Other painters remove the loose paint, then wash the siding with a soft brush or sponge, a bucket of diluted detergent and a rinse from a hose.
Once the surface is scraped and clean, you can see what’s left. If there is still intact paint or primer, you can probably just wait a couple of sunny days for the siding to dry and then repaint. To test whether the new paint will grip sufficiently to the old paint, researchers at the U.S. Department of Agriculture’s Forest Products Laboratory, in “Finishes for Exterior Wood,” recommend painting a few small sections representative of the different exposed paint layers with exterior, water-based paint. Let them dry at least overnight. Then press an adhesive bandage onto each area and yank it off. If the sticky back is clean, you’re good to go: Just repaint. If the new paint stuck to the tape, you should apply a primer before repainting. If the old paint also came off, strip all of the paint before proceeding — definitely a job for a pro, especially if there’s lead paint.
Often, cleaning and scraping leaves patches of exposed wood. In this case, you should take additional steps. Paint does not stick well to weathered wood, but a little hand sanding removes the loose fibers. Then coat the surface with a paintable water-repellent preservative, which will slow down moisture absorption in the wood and make the paint last longer. Be sure to use a product labeled as paintable, and avoid getting it on any adjoining surfaces that still have finish. Let the repellent dry for at least three days, then apply a primer to at least those areas and let that dry before repainting.
Another detail that can make a big difference is rounding over any sharp edges, such as borders between patches where paint peeled and the lower corner of siding boards. Paint on abrupt transitions and sharp corners is likely to be thin, so it cracks easily and lets in moisture. But feathering the edges and rounding over corners helps ensure that the new paint is uniformly thick, thus resistant to cracking.
If you need to prime, you can do just the problem areas or the whole house. In most cases, exterior water-based primer works fine. Oil-based primer is better, though, if you’re dealing with a lot of weathered wood or if the siding has a lot of tannin and hasn’t been painted or has tannin stains that seeped through the earlier paint, said the Sherwin-Williams customer-service agent. Western red cedar and redwood, which are often used in siding, are high in tannins, which dissolve in water-based finishes and cause brown stains on the surface. An oil-based primer blocks this movement. (Tannin stains are a cosmetic issue; they don’t cause paint to peel.)
Two coats of paint will last about twice as long as one, researchers at the Forest Products Laboratory found. That’s a great deal, considering that the prep work needs to be done just once — provided you don’t wait too long to finish the job.
Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.