Consumer Reports buys and tests various stains by painting wood panels and leaving them exposed to the elements. The best 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 in less than a year’s time.

Better for the Environment, and You 
Today's wood stains have to meet environmental rules that lower volatile organic compounds. VOCs are linked to pollution, smog, and respiratory problems, and can cause headaches and dizziness. Some may even be carcinogenic. Top stains from our tests meet these environmental standards and still looked good after the equivalent of up to three years on a deck.

Arsenic and Old Decks
Before 2004 most decks were made of lumber pressure-treated with chromated copper arsenate (CCA) 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 EPA recommends using a semitransparent stain, which tends to penetrate wood and seal in the arsenic, preventing it from leaching out. Solid 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.

Prepping Under Pressure
Washing and sanding are typical first steps. If you'll be pressure-washing a newer wood deck, read instructions before starting and cover adjacent landscaping with plastic sheeting. The pressure needed is typically 1,500 pounds per square inch; a wide-angle spray tip of 25 to 40 degrees creates a relatively wide spray that protects the wood. Angle the spray and keep it between 6 and 12 inches away from wood surfaces. For more on pressure washer safety, read this article.