- Q. What’s the best method to keep cedar siding and trim looking naturally orange and new?
A.William Feist responds: Unless you shrink-wrap each piece of cedar, it will darken and eventually weather to a silvery gray, or worse, to a blotchy dark gray. Clear finishes with UV inhibitors will slow down the weathering process, but these still need to be reapplied every two years or so. Eventually the color will change anyway, even indoors.
The best thing you can do is to approximate the color of new wood by putting on a cedar-tone stain. First, install the siding with the rough side out. A smooth surface holds less finish and weathers much quicker than a rough-sawn surface. Finish the rough surface with two coats of a lightly-pigmented, semitransparent, oil-based stain. Be sure to choose one that contains a water repellent and a preservative or mildewcide for best performance. Apply the first coat and let it soak into the wood 20 to 60 minutes and then apply the second coat. If you allow the first coat to dry, the second coat cannot penetrate into the wood. About an hour after applying the second coat, use a cloth, sponge, or dry brush to remove any excess stain. Otherwise, the stain that does not penetrate into the wood will form an unsightly film and glossy spots. Two coats of oil-based stain on rough wood will last from four to eight years, depending on the weather conditions it is exposed to.
If you have weathered and discolored wood siding, you can regain the new look of cedar by cleaning off the dirt and mildew with a solution of one third cup liquid household detergent (be sure it is ammonia-free), one quart liquid household bleach (containing 5% sodium hypochlorite), and three quarts warm water. Follow this up with a water rinse and then use an oxalic acid bleach solution made with about a half pound of oxalic acid per gallon of water. Be sure to rinse with water again. This oxalic acid bleach solution will draw out the tannins in the wood and revive the orangeish tone of the cedar. At this point, you can let the wood weather naturally, or apply the cedar-tone semitransparent stain.
— William Feist is a research chemist who specializes in coating technology at the Forest Products Laboratory in Madison, Wis.