Dianne Stow
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6/29/2007

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  Copley News Service graphic by Bob Kast

Tricks for treating redwood decks

 Q: I read your recent article on exterior wood stains. I have a question concerning our redwood decking. I would like to clean it up and put a protective coating on it, but I cannot be sure what was used the last time. The decking is in good shape, but the surface does look weather-beaten from sun and sprinkles. Would you have any points on what to do and what products are best, such as cleaners, sealers or finish coats?

A: Older wood presents a variety of challenges, particularly when youíre unsure about the previous treatments used on the surface. If you are applying a penetrating stain over previously stained wood, your choices are limited by the darkness of the previous stain, the extent of any discoloration and weathering thatís occurred, and the type of stain thatís already on the wood. The new stain would have to be darker than the existing coating to camouflage staining and weathering.

A wood brightener, a bleaching agent and cleaner, can lighten dark wood and make your color choices for a new staining product less limited. A more drastic alternative is to sand down to bare wood.

Since your decking is redwood, it is likely an oil-based product was used originally, as water-based stain products are not recommended for cedar or redwood. An exception would be in solid-color stains. If you can see the wood grain through the existing coat, it is not a solid-color stain, which hides the grain but allows some texture to show through.

Previously stained decking may look faded and perhaps isnít as vibrant as youíd like. However, that in itself doesnít mean it requires or can even accept a reapplication of a penetrating stain. A finished surface that is still intact will not allow the new stain to penetrate. If you try a new coating, you will only end up with a splotchy surface, created when the new stain is unable to penetrate the existing coating and creates glossy spots where pooling occurs on the surface.

Try this simple test on wood finished with a penetrating stain to determine if itís time to re-stain: Splash a small quantity of water against the wood surface. If the water beads up and tends to run off, the finish is still effective. If the water soaks in, itís time to re-stain.

Regardless of the resurfacing factors, the place to start is with a thorough scrubbing and cleaning of your entire decking. Both red cedar and redwood contain tannins and other chemical extractives that, when wet, can migrate to the surface, leaving brown stains (some sealers can prevent this). If this is apparent, scrub the wood with a bristle brush and a solution of 1 cup trisodium phosphate and 1 cup household bleach to 1 gallon of water. Follow this treatment by applying a commercial wood brightener.

Many commercial products are available that can brighten wood. These typically contain a bleaching agent and can remove some discoloration, but they canít completely restore the original color to weathered wood. The only way to do that is to sand down to fresh wood. An easier solution is to add color on top of the existing wood with a darker staining product.

Finish products for decks vary greatly. Until recently, stains, which were reliable in withstanding foot traffic, have been in the category of clear or pigmented stains, which penetrate the wood and do not adhere to the surface as a paint film.

Deck stains should ideally do three things: repel water, preserve the wood with a mildewcide and screen out ultraviolet rays (which are the most damaging). There are both oil-based finishes and water-based deck finishes on the market. The oil-based finishes provide more and longer-lasting protection and penetrate deeper into the wood than water-based finishes. However, water-based products are often easier to apply because they clean up with water and during recent years their durability has been improved. They are also not as susceptible to moisture conditions during application.

The wood must be clean and thoroughly dried to accept an oil-based staining product successfully. Although clear deck finishes are popular because they allow the natural grain of the wood to show through, they arenít as good at blocking UV rays. Most clear finishes loose the effectiveness of their UV protection inhibitors quickly, and need to be reapplied yearly.

The best UV protection comes from a combination of chemical inhibitors and color pigments. Therefore, you find better UV protection in products that are lightly pigmented or semi-transparent. The more pigment the finish has, the better it is at blocking UV rays. A semi-transparent deck finish will last up to three years or more before another application is needed. It also adds color to your decking while allowing some of the grain to show through.

Solid-color finishes offer the best UV protection. However, most are not formulated for foot traffic. There are exceptions and one is Cabotís solid-color decking stain with Teflon. This is a reliable surface coating developed specifically for deck surfaces.

There are numerous manufacturers of entire deck cleaning and restoration systems. Some names to look for include: Behr Process Corp., Cabot, Cuprinol Products (Sherwin-Williams), Dap, The Flood Co., Olympia (PPG Architectural Coatings) and Wolman Wood Care Products.

Be sure and follow manufacturerís instructions carefully. UV rays and foot traffic tend to wear away protective coatings. To properly maintain your deck, the following should be done annually: A thorough inspection, deep cleaning (a power washer is often a good choice, kept at the right pressure so you do not damage the wood) and reapplication of a waterproofing, UV treatment if needed.

Send inquiries to Hereís How, Copley News Service, P.O. Box 120190, San Diego, CA 92112-0190, or e-mail copleysd@copleynews.com. Only questions of general interest can be answered in the column.