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Paint adds color, freshness and protection to exterior wood

(ran HC HS HP editions)

Few things influence the look of a house exterior more than a new coat of paint. It adds style, freshness and color, whether it's the wild palette of a Victorian or the sedate tones of a Colonial. It's also a singularly American phenomenon, says architect Robert A.M. Stern.

"Other cultures built houses of masonry, but we turned to wood and, by necessity, to paint." That is because paint is far more than a decorative element.

"People put paint on their houses for looks, but what they're really doing is protecting the wood," says Tom Silva, This Old House general contractor. Paint keeps out water, which fosters rot, and blocks the degrading effects of ultraviolet radiation. It may be, in fact, the perfect preservative.

The clapboards on the recent This Old House television show project house in Milton, Mass., for instance, survived nearly 300 years before the show stripped them bare. Reprimed, then covered with two topcoats, the old siding is ready for the next century.

Bombarded by weather, baked by the sun, stretched and compressed by wood's continuous swelling and shrinking, a paint skin only five thousandths of an inch thick (think of a sheet of newspaper) can maintain its grip for only so long.

If made of the right stuff and applied to a properly prepared surface, that skin should look as good in a decade as the day it was brushed on, but, after that, even the best coatings need to be refreshed. Then it's time to pay another visit to the paint store and choose among the myriad options lining the aisles.

To make the right choice, first know what is being painted. Ask: Is it trim, siding or decking? If bare, is it redwood, cedar or pine, or is it already painted?

Then get acquainted with the ingredients, which will help you create a finish that is as durable as it is beautiful. Most oil-based paints have resins made from chemically modified soy or linseed oils (alkyds) dissolved in mineral spirits. The so-called latexes have vinyl or acrylic resins suspended in water.

The oils level out and adhere better and can be applied in cooler weather (40 degrees instead of 50 degrees for latex). The latexes are easier to clean up, less polluting and more breathable, flexible and durable depending on the quality of the resins.

Painting contractor Andrew D'Amato of Milton, Mass., uses latex for the body of the house and saves oil for the trim, where he wants a glossier sheen, free of brush marks.

However, a finish that looks picture-perfect the day after it is applied might look ragged and careworn in a year if the wood it coats was badly prepped.

"Water vapor migrating in and out of wood is the primary reason paint peels," says Mark Knaebe, a chemist at the U.S. Forest Products Laboratory. "A treatment with a paintable water repellent stabilizes the wood so paint stays stuck."

When applied to bare wood, they dramatically extend paint life. Applying more than one coat, however, may invite peeling.

Next, a coat of primer lays the foundation for a lasting paint job. Primers are paints formulated with a high proportion of binder in order to adhere tightly to wood and to the next layer of paint, but they are low in sun-blocking pigments and so need two topcoats for full protection.

Water-based primers have improved greatly in recent years, but D'Amato still prefers the oil-based varieties for their ability to penetrate and to block the stains that bleed out of redwood and red cedar.

After all the preparation, why skimp on the finish? Finding quality paint takes detective work.

Look on the label for 100 percent acrylic resins, which are generally recognized as more durable and fade-resistant than the alkyds or the similar-sounding vinyl acrylics. Also, look for high levels of titanium dioxide in light-colored paints. (Iron oxides are the pigments in dark paints.)

If the ingredients are not listed on the label, ask the paint store for a material data safety sheet. It will list some, though not all, of a paint's constituents.

Another paint option is, surprisingly, solid-color stain. Not to be confused with penetrating stains, solid-color stains are actually thin, film-forming paints that allow wood texture to show through. They brush on with ease, have no sheen and have less buildup (their film thickness is less than half that of paint), but thinness has its downside, a shorter lifespan. Two coats of solid-color stain might last six years before they need recoating, compared to eight or 10 years for paint. Like any paint, solid stains should be applied over a primer.

"Wood's great," D'Amato says, "but what's really remarkable is the paint that covers it up."

1999 Time Publishing Ventures Inc.