Refinishing Your Tired Deck
Craig Acord

Fortunately, most deck surface problems are cosmetic, not structural because decking is built of durable woods; usually redwood, cedar, or pressure-treated pine. Redwood and cedar heartwoods have natural resistance to termites and decay, pine is pressure-treated with a pesticide to give it insect and decay blocking power.

Even so, ultraviolet radiation (UV) from the sum breaks down surface fibers and lignin, causing graying and surface erosion. Moisture encourages surface mildew and causes stains, particularly in damp or humid climates. And natural extractives in redwood and cedar can discolor the surface.

The road to restoring a deck’s great looks is usually simple, regardless of the type of wood used for its construction. First you clean it, then you diagnose and treat any discoloration. And last, you protect the result with a durable finish.

Cleaning

Debris that clogs the spaced between deck boards traps moisture, encouraging mildew and rot. Blast out the debris, using a powerful nozzle on a garden hose, then push out remaining debris with a putty knife or an old handsaw. Thoroughly scrub the surface with a sudsy mixture of water and laundry detergent, using a stiff fiber brush on a long handle. Work in small areas and rinse periodically. This may be all it takes to return much of the wood’s natural tone.

For a large deck, you can rent a power washer that delivers 1,200 psi of pressure or less to blast and rinse the decking. It should have a nozzle that fans an arc of about 25 degrees to 40 degrees. Wearing safety goggles, hold the nozzle about 6 inches above the deck’s surface and spray slowly in line with the wood grain, overlapping your path. Be careful: the powerful spray can erode soft wood grain. After washing, allow the deck to dry for several clear days before applying a finish.

Eliminating Discoloration

Several products are available for dealing with discoloration and stains. Commercially-available powder or liquid-concentrates have a base of non-chlorine bleach or oxalic acid; a detergent may be part of the formula. Bleach-based products eliminate mildew, acid-based materials handle graying and stains. Some products may darken woods such as redwood and cedar, so be to test any material in an inconspicuous place.

Always wear rubber gloves, goggles, and old clothes when working with these chemicals and follow the directions explicitly. Caution: Never mix detergent containing ammonia with household bleach; the resulting fumes can be highly toxic.

Test for mildew by applying a drop of undiluted liquid household bleach to a small, black spot. If the spot disappears after a minute or two, clean the deck with a mild cleanser (no ammonia) and rinse with a solution of 1 part household liquid bleach to 4 parts water, then rinse with water. For stubborn mildew, mix one cup trisodium phosphate (TSP) and one cup household liquid bleach in one gallon of water and scrub with a stiff bristle brush. Rinse after about 15 minutes.

Non-mildew stains are often caused by natural wood extractives or corroding hardware and nails. Familiar, general graying of the decking is usually the result of surface wood cells that have been broken down by UV radiation and wear. Bleach used to kill mildew can also leave a surface drab and washed-out.

For these problems, an acid-based deck restoration product is bests. You can buy a premixed oxalic acid deck cleaner or purchase oxalic acid crystals to one quart water in a non-metallic container. Wearing rubber, eye protection, and old clothes, apply with rag to one board at a time and scrub with a soft brush. Allow to dry, then rinse with clear water.

You can strip and clean a deck that has an existing stain finish, using a commercial “ deck scrub” that you brush in and rinse off. Follow the label directions.

Finish Treatments

Though some people paint decks with deck paint, most choose to take advantage of the natural beauty of expensive decking woods by applying a cleat or lightly stained finish. If you chose to paint, use a stain-blocking oil or alkyd primer first.

In general, the best finished are those that soak into wood, not those that provide a surface film. According to Bill Evans, Technical Coordinator at Thompson & Formby, “ A heavily pigmented, solid stain isn’t really recommended for decking because it shows wear patterns and may tend to peel. You want some something that really soaks in.”

There are three important characteristics to look for in a finish. First, the finish should be “water repellent” or” water proof”, not just “ water resistant.” Second, it should offer UV (ultraviolet) protection. And third, if mildew is a potential problem, the finish should contain a mildewcide, which a “wood preservative” does. Regular preservatives should be reapplied once a year, newer and better “ toner” products offer more UV protection and may last up to four years. Whatever product you choose, read the label to be sure it’s right for your deck. Buy quality materials and follow the manufacturer’s directions for application. Your result will be deck that provides you with years of lasting beauty and enjoyment.