Seal decks and other outdoor wood


June 20, 1992|By Gene Austin | Gene Austin,Knight-Ridder News Service

Wood with a natural appearance is popular for such uses as home siding, decks, fences and outdoor furniture, but a handsome bare-wood look can be short-lived unless the wood is given some protection and maintenance.

Even pressure-treated wood, which is widely used for decks and fences because of its resistance to rot and insects, can become unsightly in a few years if left on its own.

Among the problems that can affect outdoor wood, besides rot and insects, are discoloration, caused by mildew, fungi and dirt, and splitting and warping, caused by water and sun. These problems may be avoided or reduced by regular cleaning and sealing with a water repellent.

The need for cleaning and sealing varies with the climate and exposure, but decks and outdoor furniture usually need treatment every two or three years. These, along with fences and other smaller structures with relatively easy access, can generally be maintained by do-it-yourselfers. Siding and wood roofs are best maintained by trained technicians with special equipment, such as pressure washers.

In general, any dirty or deteriorated wood should be cleaned before sealing. Overall cleaning can often be skipped if the wood is relatively new and unsoiled, but any dirty areas should be sanded or cleaned with a detergent before sealing.

New construction should be sealed as soon as the wood is adequately dried, which can vary from immediately to several months. Wood that is heavy and damp to the touch usually has high moisture content. Consult instructions on sealer containers for specific timing of application; if in doubt, wait about 60 days after construction.

An exception to the quick-sealing rule is pressure-treated wood that is factory-treated with a water repellent as well as preservative. These double-treated woods are sold under special brand names at extra cost; they generally do not need sealing for 18 months to two years after construction.

Here are some tips on buying and using cleaners and sealers:


Many wood cleaners are sold at home centers, lumber yards and paint stores. Most are in powder form, to be mixed with water before use.

Application instructions for cleaners vary and should be read carefully, along with precautions for safe handling and use (always wear goggles). A garden-type, compressed-air sprayer is a convenient way to apply most cleaners. Special spray applicators are sold by some dealers.

After application, most cleaners should be allowed to work for a designated time, then the area should be scrubbed with a stiff-bristle brush. The wood is then rinsed and allowed to dry thoroughly before a sealer is applied. Very soiled wood might require spot treatment of difficult stains as well as overall cleaning.

Plants can be harmed by some cleaners and should be covered or rinsed immediately after contact (consult instructions).


Clear sealers or water repellents are designed to help prevent water from soaking into wood. Some water repellents also contain preservatives to help reduce decay; these are good choices for any wood that is not pressure-treated, including redwood and cedar.

Repellents and repellent-preservatives are sold under a wide array of brand names. Always read instructions and specifications completely before buying, since different sealers can have different effects.

Many sealers contain strong solvents that can be unpleasant and/or harmful to breathe. Wear a respirator mask if possible with these sealers, or set up a fan to disperse the fumes. Goggles should be worn when using any sealer, and rubber gloves are needed with some, so check precautions. Application instructions should be followed carefully.

When does outdoor wood such as decking need resealing? A good test is to sprinkle some water on the wood. If the water quickly soaks in, the wood needs sealing. Water will form beads on the surface of wood that has active sealer.

Readers' questions and comments should be sent to Gene Austin, c/o The Baltimore Sun, Box 8263, Philadelphia, Pa. 19101.

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