Q: Our 3-year-old cedar deck is on the southwest side of the house and gets lots of sun. What can we do so we don't have to restain it every spring?

— Ethan, Union, MO

A: Tom Silva replies: Although the best way to protect wood from the sun is to coat it with paint or an opaque stain, sometimes called a solid-color stain, these products aren't great for decks because they tend to trap moisture against the wood and eventually peel. A semitransparent stain is a better choice because it has pigments to block most of the harmful UV rays but doesn't form a film that can peel. These stains come in oil-based and water-based versions. I find that oil-based stains are easier to apply evenly and tend to last longer.

Before you apply the stain, you'll need to sand off the existing finish as well as any gray wood, which won't hold a finish very well. So first, set all the nails or screws just below the surface of the decking. Then, rent a random-orbit floor sander — it's gentler than a drum sander — and use 80-grit paper to get down to fresh wood. Proceed carefully, taking off only as much wood as needed. When you're done, vacuum all the dust and coat the deck right away with the semitransparent stain. Research by the U.S. Forest Products Laboratory shows that even a few days of exposure to sunlight can affect the wood's ability to accept stain properly.

Keep a close eye on the stain over the next couple of seasons. You should get at least three years out of a good semitransparent. But if you see places where the finish has worn thin and exposed the wood grain, it's time to scrub the deck clean — no sanding needed this time — and apply more stain.
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