applying clear coat
Photo: David Carmack
How Clear-Coats Work
"Guaranteed to prevent graying." "Restores wood's moisture content and helps it stay flexible." "Stops cupping, cracking, curling, and warping."

Judging by the labels on the cans of exterior-grade clear finishes at paint stores and home centers, the job of keeping wood looking good seems downright easy: Just brush one of these products on a mahogany entryway, a redwood deck, or cedar siding, and the wood will stay as fresh and bright as the day it was cut.

The truth is, though, that shielding wood from the elements without resorting to an opaque blanket of paint is not that easy. Assaulted by water, ultraviolet light, and mildew spores while they try to cope with wood's tendency to shrink and swell, some finishes peel like sunburned skin or are little more than solvents that just evaporate into thin air.

Fortunately, advances in coatings technology have created new formulations that actually live up to their billing, as long as they are lovingly maintained.

Clear finishes work in one of two ways: either by forming a hard film over wood or by penetrating it. The film-forming products—both classic varnishes and modern urethanes—are unmatched in their ability to bring out the beauty and depth of a wood surface while guarding against wear and tear. But they're often demanding to apply and always unforgiving of neglect: If not lightly sanded and recoated every one to three years, the film will begin cracking and peeling, and then must be stripped down to bare wood. Penetrators, on the other hand, preserve wood by soaking into its fiber and so do not peel or require scraping or sanding; the finish simply wears away. Compared with hard coatings, they do a better job of letting damp wood dry out, and they can be recoated without elaborate surface preparation. But even the best ones need a routine reapplication just as often as film-formers, and do little to guard the wood surface from dirt and wear.

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