Getting started

To see how well each deck treatment we tested protects, we built a deck behind our Yonkers, N.Y., headquarters and coated sections with various deck treatments and wood stains. Then we left the deck exposed to whatever Mother Nature dished out. The best we tested still remained close to their original color after three years, picked up only a little dirt and mildew, and effectively protected the wood from cracking. The worst looked ratty and provided little protection after just one year.

While the longest-lasting products were often the most expensive up front, their longer life should save you money over time. Don't buy strictly by brand; different products from the same manufacturer often performed differently. What's more, a product that worked well for you last time may not do as well this time, as manufacturers keep reformulating to address cost and performance, and to comply with government safety standards.

Wood stains must meet new environmental rules that lower volatile organic compounds. VOCs can cause acute symptoms such as headaches and dizziness, and some may be carcinogenic. But manufacturers admit that removing VOCs from wood stains and treatments without reducing performance is a challenge. Although many of the products in our latest test group performed well, none did quite as well as the best in our previous group.

Before 2004, most decks were made of lumber pressure-treated with chromated copper arsenate to fend off rot and insects. But concerns that arsenic, a toxin, could leach into the soil led to the introduction of other preservatives. If the wood in your deck is pressure-treated with CCA, the U.S. Environmental Protection Agency recommends using a semitransparent stain, which tends to penetrate the wood and seal in the arsenic, preventing it from leaching out. Opaque treatments also seal well, but they may flake or peel and require sanding, which would spread arsenic-laden dust from CCA lumber. If your deck is made of CCA lumber and its finish is flaking, we suggest calling a pro equipped to safely remove the old finish, dust, and debris.

Types

Finishes vary according to how much of the wood's natural grain they show. The best opaque treatments tend to last the longest. But you may prefer a semitransparent or clear finish for aesthetic reasons. The cost of all types of wood stains and treatments is $15 to $50 a gallon.

Also known as solid-color stains, opaque treatments typically hold up for at least three years--the longest overall. They're fine for pine decks, where seeing the grain isn't important. On the downside, they hide the wood grain the way paint does. Opaque finishes might also build up a film, especially after several coats, which can peel, chip, and crack like paint. That's a concern with older decks made of arsenic-laden, CCA lumber.

Although generally not as weather-resistant as opaque treatments, some semitransparent products go the distance better than others. Semitransparent products let some of the wood grain show through, making them a good choice for cedar, redwood, and other costly woods that you want to show off. But they range from little pigment to nearly opaque. And even the best we tested needed refinishing after two years.

These may contain only a little pigment, along with water repellants. They're ideal for showing off the natural grain of a premium wood as much as possible. Clear treatments may have ultraviolet inhibitors and wood preservatives. But with most, deck refinishing is an annual chore.

Features

Synthetic resins--alkyds and latex--have largely replaced linseed oil and tung oils. Manufacturers describe them as preservatives, protectors, stabilizers, repellants, sealers, cleaners, restorers, or rejuvenators. Neither alkyd- nor latex-based treatments showed any clear advantage in our durability tests.

Latex-based stains and treatments allow easy cleanup with water.

Most alkyd (oil based) products require cleaning with mineral spirits, though a few can be cleaned with water.