Q: We have wainscoting halfway up the wall in our small bathroom. I believe the wainscoting is original to the house, so about 20 years old, and I think it was spray-painted before installation. It has very thin vertical grooves in the wood as part of its pattern, with two grooves/lines every 1½ inches. We repainted the white trim, and now the wainscoting looks yellow in comparison. How can I repaint the wainscoting, given the small grooves?

Bucks County, Pa.

A: You have what’s known as beadboard wainscoting, though in a modern version. The original type consisted of separate boards milled with overlapping edges. Because wood swells and shrinks primarily across its width, the boards were shaped so they could change width without cracking or popping loose. The expansion gaps were built into the design, resulting in the vertical lines you see.

Today, it’s still possible to buy board-style beadboard. But builders usually create the look with panel or plank products that mimic the look and are faster to install. Some panels are made of compressed wood fibers, either medium-density fiberboard (MDF) or high-density fiberboard (HDF). The vertical grooves are milled in as a design feature but serve no practical purpose, except for where pieces join. Plywood beadboard also exists, but the vertical grooves cut through more than one of the layers used to make plywood, so the grooves are rough at the bottom, unlike with all the other options. For use in a bathroom, where walls can get steamy or wet, there is special moisture-resistant MDF beadboard and beadboard planks made of PVC or other types of vinyl, which is impervious to moisture damage.

From the pictures you sent, it’s clear that you have one of the modern versions. The surface is too uniform for it to be individual planks. It’s impossible to know from looking at a picture what type of material you have, but paint will probably stick well, even if you have a vinyl/PVC type. The products sold at Home Depot, for example, are paintable. Some are sold pre-painted, while others are primed.

Because we don’t know whether your beadboard was factory-finished, primed or painted on-site, or even what material is under the paint, take time to prepare the surface as if it were vinyl. What works for that should work for all other types. But, as always, when you are recoating a surface that has a finish you’re not certain about, do a small test patch with the primer and topcoat to ensure everything sticks.

Wipe down the wainscoting to get off any soap splashes or grime. When dry, lightly sand to scuff up the surface and help the paint grip. You want it to look evenly dull. Don’t worry about scuffing up the grooves, although it wouldn’t hurt to fold a piece of sandpaper and quickly run it down each line. Wipe away the sanding debris.

Apply a primer formulated to stick to slick surfaces. Plastpro (plastproinc.com), which makes the Veranda vinyl beadboard sold at Home Depot, recommends Sherwin-Williams’s PrepRite Bonding Primer, which has since been renamed Extreme Bond Primer ($66.19 a gallon, sherwin-williams.com). But other brands of bonding primer should work, too. A water-based primer is fine. Wait the time recommended on the label of the primer to apply the finish paint. For the Sherwin-Williams primer, that’s one hour for most paints, but 24 hours if the paint is a high-performance finish, which, in Sherwin-Williams’s lineup, usually means “pro” is in the product name. To be safe, wait a day. Apply two coats of the finish paint, waiting the time the label recommends between coats.

Now for the focus of your question: What painting tool or tools to use? For its primer, Sherwin-Williams recommends either a nylon/polyester brush or a roller with a soft, woven roller cover that has a ⅜ -inch nap. For your project, having both tools will probably work best. If you were painting beadboard before installation, it would be relatively easy to do the job with just a roller. You could load the roller liberally with paint, then roll it on with enough pressure to squish paint into the crevices. But when the beadboard is already installed, using only a roller creates too big a risk of creating drips of excess paint.

You’ll probably have better luck by using a roller to get paint onto the wall and mostly into the crevices, then quickly following up by brushing with a mostly dry brush to even out thick or thin areas and whisk away paint globs, especially in the grooves, before they dry into visible drips. It’s important to avoid repeatedly brushing over an area, because that keeps the paint from drying properly. The second coat of paint should create the uniform look you’re after. If the first coat leaves bare areas in the grooves, make the second coat all about them, using just the brush. Once that dries, apply a third coat, during which you focus on the flat areas.

For the specific tools, an angled sash brush that’s 1½ or two inches wide should work; the tip and the angled shape will get into the crevices and still allow you to smooth over paint on the flat areas. A regular-size roller can be tricky to use in a small space. A small roller about the size of a hot dog is more nimble and easier to control. Get two roller covers: one for the primer, one for the finish paint. Wrap the roller tightly in a plastic bag between the finish coats.

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