A regular maintenance program can improve the appearance of your wood deck and significantly extend its life. The primary causes of wear are moisture and sunlight. Moisture can be trapped on the deck by leaves, debris, or items stored on the deck, such as planters. Debris tends to collect in the spaces between deck boards, trapping moisture, which causes decay in the deck framing. The shady underside of the deck is more likely to be damaged by decay. A putty knife, another narrow tool, or a hard spray of water from a garden hose can remove the debris from between the deck boards. If the deck boards are too close together, they can be widened to approximately 3/16 inch by using a circular saw.

To clean an older deck and improve its appearance, scrub it with a stiff brush and a solution of TSP (trisodium phosphate) in warm water; mix one cup TSP crystals into a gallon of water. Be sure to wear rubber gloves and, if you are scrubbing by hand, wear protective goggles. If you are going to be working on your hands and knees, rubber kneepads would be helpful. After scrubbing, hose off dirt and solution with water. If areas of the deck are discolored with mildew, apply a solution of one part water to three parts household bleach to the stained areas. Commercially prepared deck cleaners are also available. Some cleaners contain fungicides and mildewcides and others contain special bleaches to lighten the wood.

For large, heavily soiled decks, a power washer is ideal to clear off surface grayness and save a lot of scrubbing and effort. A power washer with a 2,000-pound per square inch pressure pump rents for about $25 per hour or $75 per day. These sprayers are very powerful and special care should be made to avoid damaging the wood. Be sure to wear safety goggles. After the deck is clean and dry, examine the surface carefully for loose boards, nails, and other damage. Use a nail set to punch nails below the deck surface.

Oxalic acid can make your just-cleaned deck look almost new. Oxalic acid is sold at paint or hardware stores and it lightens and brightens the wood as you apply it. It is also useful for removing stains. Oxalic acid causes skin irritation so wear rubber gloves and protective goggles when handling it. Avoid contact with nearby plants. Mix four ounces of crystals to one gallon of warm water. Apply liberally with a sponge, mop, or garden sprayer, but do not use metal buckets, wire brushes, or steel wool. The more time it takes to dry the better it works, so try to work in the early morning or on an overcast day, rather than in the full sun. Let the solution act on the deck; then thoroughly hose off the surface. The deck may look quite new when finished, but do not expect this to last. The deck will slowly gray with time and sun exposure.

There are stains that can restore the original color and keep it looking new. Water repellents or wood preservatives can help maintain deck appearance. Read the manufacturers' recommendations on these products for coverage and application methods. These products should be applied with a brush to allow for adequate penetration of the material into the wood. Do not apply these materials in direct hot sunlight, as you want it to soak into the wood instead of evaporating. Reapplication of these materials may be necessary every three to four years, depending on the amount of sun exposure and climate in your area.

The framing beneath the deck should be examined periodically for signs of decay. This is usually indicated by a white or brown growth on the surface of the wood, followed by softness and deterioration. Minor decay can be treated by wire brushing the surface and applying a fungicide such as copper napthenate (Copper Green) to the area. Probe the wood with a screwdriver to determine if it has weakened.

Any wood that is seriously weakened by decay should be replaced. If it looks like there are areas of significant damage it is probably best to hire a deck specialty contractor to make repairs, especially if the deck is high off the ground.