In this article:
• Cleaning
• Eliminating Discoloration
• Finish Treatments
A new wood deck provides a warm, handsome connection with the outdoors, adding to a home's beauty and setting the stage for a world of outdoor activities. But decks take a lot of abuse, both from use and through continued exposure to weather. After a few years, without proper care, they become weathered and uninviting.
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 a 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 sun breaks down surface fibers and lignin, causing graying and surface erosion. Moisture encourages surface mildew and causes stains, particularly in damp or humid climates where surfaces never completely dry. 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. First, you clean it, and then you diagnose and treat any discoloration. Last, you protect the result with a durable finish.
If you're working on a deck that is above a usable area, such as a second-story deck above a patio, before beginning be sure to protect the area below it with plastic sheeting or dropcloths.
Cleaning
Debris that clogs the spaces between deck boards traps moisture, encouraging mildew and rot. Blast out the debris using a powerful nozzle on a garden hose, and then push out any remaining debris with a putty knife or a laminate scoring tool like the one shown here.
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 up to 1,200 psi of pressure to blast and rinse the decking. It should have a nozzle that fans an arc of about 25 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. After washing, allow the deck to dry for several clear days before applying a finish.
HomeTips Pro Tip: When using a power washer, be careful! The powerful spray can erode soft wood grain.
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 products handle graying and stains. Some products may darken woods such as redwood and cedar, so be sure to test any product in an inconspicuous place.
Always wear rubber gloves, goggles, and old clothes when working with these chemicals, and follow the directions explicitly. 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, and then rinse. For stubborn mildew, mix 1 cup tri-sodium phosphate (TSP) and 1 cup household liquid bleach in a gallon of water and scrub with a stiff 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 best. You can buy a pre-mixed oxalic acid deck cleaner or purchase oxalic acid crystals from a hardware store or home improvement center and mix a solution of 4 ounces crystals to 1 quart water in a non-metallic container. Wearing rubber gloves, eye protection, and old clothes, apply with a rag one board at a time and scrub with a soft brush. Allow to dry, and then rinse with 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 clear or lightly stained finish. If you do choose to paint, use a stain-blocking oil or alkyd primer first.
In general, the best finishes are those that soak into the wood, not those that provide a surface film. A heavily pigmented, solid stain isn't really recommended for decking because it shows wear patterns and may tend to peel. You want something that really soaks in.
There are three important characteristics to look for in a finish.
- It should be water repellent or waterproof, not just water resistant.
- It should offer UV protection.
- If mildew is a potential problem, it 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 a deck that provides you with years of lasting beauty and enjoyment.
