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Deck Cleaners, Stains & Sealers

Looking for the best decking treatment? A guide to the cleaners, finishes, and techniques for making your wood deck look new again.

Stained Wood Deck

Even if your deck is made of pressure-treated lumber, redwood, cedar, or some other durable species, it's at risk the moment the last nail is driven home. There are several culprits. Moisture swells the wood while the burning rays from the sun dry and shrink it, causing cracks and checks while also encouraging warping. Ultraviolet rays also discolor wood and accelerate wear by breaking down wood fibers.

Add in the scratches that occur when you drag chairs across the surface, splattered grease from barbecues, mold growth in shady spots, and ground-in dirt from foot traffic, and most decks start to look old within a few years.

Reversing the damage is simple enough. Apply a specially formulated cleaner and then treat the surface with a water-repellent finish. It's a systems approach where all the elements work together. Dirty decks won't accept a finish well; dirt can also react with the finish and turn the lumber black. And even the cleanest deck surface is at the mercy of the elements without the right finish.

Choosing from among the several hundred deck cleaners, stains, and sealers out there is less simple. You'll also have to decide whether to do the job yourself or hire a pro. Here's how to take the guesswork out of renewing a worn deck or protecting the one you just built.

Time, Cost and Materials

Most homeowners do the work themselves because they can save money. The materials for a 20x20-foot deck will run between $80 and $120, plus another $80 or so to rent a power washer for a day. What's more, the actual work takes just two days — one to clean the surface and another to apply the finish. But you will have to wait three to five days after cleaning for the deck to dry so the finish will penetrate fully.

If you don't have the time to do it yourself, you can hire a deck-maintenance contractor. But the relative newness of this specialty means most of the pros don't have much experience. That makes checking references and visiting past jobs especially crucial. And because most pros have their favorite products, you'll probably have little say about the ones used on your deck. Expect to pay between 60 cents and $1 per square foot for materials and labor — up to $400 for a 20x20-foot deck.

Best Deck Cleaner

Deck cleaners get rid of mold, mildew, and any dirt or stains imbedded in wood fibers. Though you can mix your own with laundry detergent and bleach, a store-bought cleaner is best for very dirty or damaged wood.

These products fall into two categories: cleaners and restorers. Among the leading makers are Thompson's, Wolman, and ZAR. Cleaners contain detergent and bleach and work best on dirt and mildew. Restorers contain oxalic acid and are ideal for removing tannin streaks and stains around nail- and screwheads in cedar and redwood decks. Both come in liquid and crystal form and cost about $15 for enough to make 5 gallons of solution (good for 750 to 1,000 square feet of deck area).

If your deck was painted or sealed with varnish (a big mistake), you'll need to remove these high-maintenance finishes with a deck stripper before cleaning. Whether you use a stripper or wood cleaner, or both, apply it with a roller or stiff-bristle push broom. Wait a few minutes for the product to soak in. Then rinse with a hose or power washer. Remember to clean the exposed ends of cut deck boards.

A Wood Deck With Semitransparent Finish
COLOR PIGMENTS in semitransparent and solid-color finishes help protect wood from UV rays. Use finishes designed for decks; products meant for siding won’t stand up to foot traffic.
Photo by Crandall and Crandall

Best Deck Sealers & Stains

Deck finishes fall into two categories: sealers and stains. Both are formulated to seal out the elements. As their name implies, clear sealers are nonpigmented finishes. Stains are available with a little pigmentation (referred to on the label as "tone"), semitransparent, and in solid colors. Unlike paints, which form a surface film, clear and pigmented finishes penetrate the wood and can stand up to foot traffic.

"The ideal deck finish does three things," says Charles Jourdain, vice president of technical services at the California Redwood Association, a lumber-industry trade group. "It repels water, preserves the wood with a mildewcide, and screens out UV rays." Some products waterproof only. For maximum protection, the label should list all three features.

Oil- or water-based finish?

Deck finishes are either oil- or water-based. Which you choose depends on your priorities. According to Mark Knaebe, a chemist with the U.S. Department of Agriculture Forest Products Laboratory who evaluates deck finishes, oil-based finishes provide more and longer-lasting protection. "Oil-based finishes penetrate deeper into the wood than water-based finishes," Knaebe says. Familiar names here include Cabot's, DAP, Flood, Olympic, Thompson's, and Wolman.

On the other hand, water-based products are easier to clean up than oil-based products. They're also more forgiving in damp conditions, explains deck-maintenance contractor John Sundquist, of Northbrook, Illinois, based American Deck Maintenance: "While the wood surface must be bone-dry before it accepts an oil-based sealer, damp wood can absorb a water-based product." Water-based finishes also last longer than they did just a few years ago. Companies like Wolman and American Building Restoration Products (X-100 Natural Seal) make a water-based version of their product.

Clear or color finishes?

Clear deck finishes are popular because they allow the natural grain of the wood to show through. And because they're transparent, you can't leave any lap marks during application, which is a common problem with pigmented finishes. But, they aren't as good at blocking UV rays.

The best UV protection comes from a combination of chemical inhibitors and color pigments. Though inhibitors in some clear finishes slow UV penetration, they tend to break down relatively quickly. The result is that most must be reapplied yearly.

Lightly pigmented and semitransparent finishes add color to the deck while allowing some of the grain to show through; they also form an effective UV barrier. The more pigment the finish has, the better it is at blocking UV rays. That's why a semitransparent deck finish will last up to three years or more before another application is needed.

Solid-color finishes offer the most UV protection. Unfortunately, most aren't formulated for foot traffic. If you want a solid color, look for products made expressly for deck surfaces, such as Cabot's solid-color decking stain with Teflon.

For do-it-yourselfers, there are two drawbacks to pigmented finishes. They leave lap marks or areas where the finish is uneven if you don't apply them carefully. They also show traffic patterns as they wear, which requires spreading extra finish into affected areas during reapplication.

Figure on spending $15 to $25 per gallon for a good clear or pigmented deck finish. Finishes that cost less probably won't provide all of the protection your deck needs.

Shaded Decks Should Have Finish That Contains Mildewcide
HEAVILY SHADED DECKS are prone to mildew. After initial cleaning and finishing, apply a deck cleaner annually to help keep mildew at bay. Make sure the finish you use contains a mildewcide.
Photo by Bill Matthews

How to Apply Deck Stain & Sealer

Waiting nine months to a year before applying finish to a new pressure-treated-wood deck used to be standard procedure. Leaving wood unprotected lowers the interior moisture content and allows the pores to open and accept more sealer or stain. Unfortunately, it also contributes to weathering.

Instead, apply finish on a new or newly cleaned deck within a few weeks. Then apply a second coat the following year. "That second application leaves more finish in the wood. Doing it right also lets you wait two or three years before putting on another coat," says the USDA's Knaebe.

The one exception to finishing right away is new lumber that has a waxy buildup. This mill glaze won't allow the finish to penetrate and any finish applied to it will peel off in a few months. You'll know it's there if water from a hose beads on the surface. Mill glaze can also appear as a burnished area. In either case, wait two or three weeks so the surface can weather. If water still beads up, sand lightly.

Apply the finish when the temperature is above 50°F and the weather will be dry for a few days. Follow directions; these tips apply to all products:

  • Wear eye protection and long pants and sleeves. Also wear rubber gloves, especially when using a stripper.
  • Before applying a finish or cleaner, protect surrounding vegetation by wetting it with a hose and covering it with plastic tarps. Rinse again when done.
  • Finish the top, exposed sides and — on new decks — the bottom of boards, if possible. Also coat any structural members you can reach. Future maintenance can concentrate on surfaces and end grain exposed to the weather.

Relaxing on a deck is a great way to enjoy the outdoors. The right care will prolong your enjoyment by protecting the surface of the wood for years to come.

Deck With Slight Pigmented Finish
FINISHES WITH slight pigmentation provide natural beauty and let you avoid lap marks. Look for “tone” on the label.
Photo by Bill Matthews

Where To Find It:

American Building Restoration Products
9720 South 60th Street
Franklin, WI

100 Hale Street
Newburyport, MA 01950

Cuprinol Products
101 Prospect Avenue
Cleveland, OH 44115

855 North 3rd. Street
Tripp City, OH 45371

The Flood Company
1212 Barlow Road
Hudson, OH 44236

1 PPG Place
Pittsburgh, PA 15272

Osmose Wood Preserving
Drawer 0
Griffin, GA 30224

Box 1569
Ukiah, CA 95482

The Thompson's Company
101 Prospect Avenue, NW
Cleveland, OH 44115

Wolman Wood Care Products
436 7th Avenue
Pittsburgh, PA, 15219

Box 70
Scranton, PA 18501

Equipment manufacturers:
Campbell Hausfeld
100 Production Drive
Harrison, OH 45030

Wagner Spray Tech
1770 Fernbrook
Plymouth, MN 55447

California Redwood Association
405 Enfrente Drive, Suite 200
Novato, CA 94949

Southern Forest Products Association
Box 641700
Kenner, LA 70064

United States Department of Agriculture
Forest Service, Forest Products Laboratory
1 Grifford Pinchot Drive
Madison, WI 53705

Western Wood Products Association
522 SW 5th Avenue, Suite 400
Portland, OR 97204

Also featured in the article:

American Deck Maintenance
Box 781
Northbrook, IL 60062

Mr. Deck
Box 507
San Martin, CA 95046