A Hidden Layer of Protection Makers of wooden windows and doors have a secret: Coating bare wood with a paintable water-repellent preservative keeps paint on longer. Now, Andrew D'Amato and a few other top-of-the-line painters are borrowing the trick, which is backed up by research at Purdue University and the U.S. government's Forest Products Laboratory in Madison, Wisconsin. It's important that a product's label make three claims: "water repellent," "preservative" and "paintable." The water repellent, often a wax, keeps the wood from shrinking or swelling as much when it rains, so the paint stretches less, stays intact and grips the wood longer. The preservative kills mildew, which could grow into the top paint layer and ruin its look, and fungi that cause wood to rot. There is a wide variation in formulas on the market, however. To find an effective preservative, follow the lead of the many window and door manufacturers who use products that contain 3-iodo-2-propynyl butylcarbamate, an iodine-based preservative often abbreviated IPBC. (Preservatives are usually listed on labels.) Repellents not labeled "paintable" may contain so much wax that paint won't stick. When in doubt, test first in an inconspicuous area. "After the paint is dry, press a piece of adhesive tape on it," says Alan Ross, vice president and technical director for Wolman Wood Care Products, which makes water-repellent preservatives. "When you pull it up, does it pull up the paint? Compare it to an area where you haven't put the repellent." Bad painters brush paint on bare wood. Good painters prime first. But D'Amato and other excellent painters follow the recommendation of the Forest Products Laboratory in Madison, Wisconsin?they pretreat bare wood with a clear, paintable water repellent to keep the siding from absorbing moisture that gets past the paint. After the repellent dries, the crew masks windows with blue painter's tape and builder's paper and applies an oil-based primer. "We spray it on, then brush it out," says D'Amato, expertly sweeping and stabbing with a natural-bristle brush to work the wet primer into cracks and crevices. He prefers oil-based primers because they penetrate better than latexes do. The primer, however, raises the grain. So, D'Amato's crew smooths the dried film with light passes of a palm sander fitted with 100-grit paper, then sweeps off the resulting dust with a soft-bristled shop brush. In the course of 133 years, D'Amato's house has collected cracks, crevices and dings which are unsightly and accelerate leaks and rot. So he guns on 25-year latex-acrylic caulk, patrolling every square foot of the exterior. He seals around trim but leaves cracks between clapboards, so moisture can escape from the house's interior; if the whole exterior were sealed tightly, migrating moisture could make the paint bubble and peel. For clapboards, D'Amato chooses an airless sprayer, which pumps paint fast (but also wastes much in overspray). For detail work such as lattice, he switches to a high-volume low-pressure sprayer. It ejects less paint but is more accurate.
Caulking finished, D'Amato sprays on another coat of primer. "Now all of the caulk is sealed between two coats of primer. It's not essential, but at this point it's easy?you've already got the sprayer out and the windows masked off, so why not?" Finally, the painter paints. "My wife, of course, couldn't pick out a chip, so we had this custom color mixed up," he says, waving at the burnt-orange shade of flat latex in the open can. After all of the prep work, this long-awaited metamorphosis seems almost instantaneous. "We just spray it on. The surface is already perfectly smooth, so there is no need to brush it in." D'Amato applies two coats. A sprayed-on coat is thicker, and some is lost to overspray, so a gallon covers about 250 square feet instead of the usual 500. D'Amato sprays as lightly as possible, in keeping with a fundamental rule: Two thin coats are more durable than a single thick one. He paints the body of the house first, then progresses to the trim, brushing on two coats of an appealing glossy off-white around doors and windows. "I always go with an oil-based paint for the trim coat," he says. "I like its sheen. You can work it longer. You don't have to worry about it drying up and leaving ugly lap marks."
Ask TOH users about Painting

Contribute to This Story Below

    More in Painting & Finishes