How often should a deck be stained or sealed?

Most decks with a semitransparent stain need a fresh coat every two to six years, depending on the wood, and decks with a clear or lightly tinted sealer every year or two. The exact interval depends on the product, the wood, and how much sun and rain the deck takes. Instead of a calendar, use the deck itself: when water stops beading on the boards, the finish is done.

What to expect from each kind of finish

The USDA Forest Products Laboratory's Wood Handbook gives these rough service lives for decking, compiled from many researchers' observations:

• Semitransparent stain: a semitransparent stain lasts about 2 to 3 years on new, smooth deck boards and about 3 to 6 years on weathered or rough ones.^[1]
• Tinted finishes such as deck finishes: Lightly tinted deck finishes last about 1 to 2 years on new boards and 2 to 3 years on weathered ones.^[1]
• Clear water-repellent preservatives: "As a natural finish, the life expectancy of a WRP is only 1 to 2 years".^[1]
• Paraffin-oil stains: Penetrating stains that use paraffin oil as the solvent last about a year,^[1] though they are easy to reapply.

Those are averages; the handbook notes that expected life depends on climate and exposure.^[1] Three patterns are worth knowing:

Smooth new wood holds less stain. For semitransparent stain, the handbook says: "If used on smooth wood, expect approximately half the service life compared with saw-textured surfaces".^[1] That is why a brand-new deck with smooth boards may need recoating sooner than you would expect.

The second time lasts longer. "The subsequent application of penetrating stain often lasts longer than the first because it penetrates the porous weathered surface."^[1]

Sun is the clock. "The shaded side of a structure may not need to be re-stained nearly as often as the sunny side."^[1] Open, sunny boards and stairs usually wear out first; shaded railings can go much longer.

How to tell it is time

Water no longer beads. Sprinkle water on the boards. When a drop of water soaks in quickly, the finish has lost its water repellency.^[1] Sometimes the color still looks fine: the handbook notes that if there is still enough pigment on the wood, adding a clear water repellent may be all that is needed to provide another year of protection.^[1]

Mildew appears. In the handbook's words: "Mildew growth on surface usually indicates the need for refinishing."^[1]

The wood turns gray. As penetrating finishes weather, they lose their water repellency, turn gray, and develop mildew.^[1] A penetrating stain fades rather than peels, so graying and lost color are the normal signs it is due.

Why it is worth keeping up

Decks rarely fail first from rot. The handbook notes: "The most common reason for removal of preservative treated wooden decks is splitting and checking, not decay or structural problems."^[1] It adds: "The best way to prevent checking and get 40 or more years of service life from wood is to ensure water beads up on the wood surface rather than soaking in immediately."^[1] Regular recoats are what keep water beading.

New pressure-treated decks need it too. The handbook says copper-treated lumber may keep its brown color for about two years,^[1] and even if the manufacturer added a water repellent to the treatment, the wood still needs a finish to last.^[1] Let new wood dry out first, then finish it.

Color choice matters. Darker finishes absorb more solar heat, which leads to more warping and checking than lighter colors,^[1] so a lighter stain can be easier on the boards.

Older CCA decks. For a deck built with CCA-treated wood, the EPA says applying a penetrating protective coating (such as oil- or water-based stains) on a regular basis may reduce the leaching of chemicals.^[2] The U.S. Consumer Product Safety Commission advises not to use harsh cleaners such as bleach, sodium percarbonate or oxalic acid on CCA-treated wood, and to avoid sanding or power washing it,^[3] so clean those decks gently.

A simple yearly routine

Fairfax County's building official recommends that you evaluate your deck annually and have it inspected regularly by a licensed contractor, more often as the deck gets older,^[4] and in winter to shovel the snow off your deck after a heavy snow fall to minimize the burden and wear.^[4]

When it is time to recoat, the prep is light for a penetrating stain: the handbook suggests a dry stiff-bristle brush to remove surface dirt, dust, and loose wood fibers^[1] before restaining, and says to remove mildew before refinishing.^[1] Where some areas still have good stain and others are worn, feather the new stain into the old.^[1] The full method is in how to stain a deck; if the finish is lifting rather than fading, see why deck stain peels.

Stop and call a pro if

• You find soft or rotted wood, large splits, wobbly railings, loose stairs, or rusted connectors and fasteners during your yearly check.
• The finish is peeling in sheets rather than fading, which usually means stripping before restaining.
• The deck is high enough that recoating the railings or rim means working from a ladder.

Getting help on Loclis

On Loclis you can describe a deck staining job once and local businesses quote it. See what deck staining costs, browse deck staining and sealing, find exterior pros around Blacksburg, or read more exterior answers.