How do I stain a deck?

Use a penetrating, oil-based semitransparent stain, not paint or a solid-color stain. Then the job comes down to three things: a clean, dry deck, thin coats brushed on a few boards at a time, and wiping off whatever the wood does not absorb. Most of the trouble people have with deck stain comes from skipping one of those.

Choose a stain that will not peel

Deck boards sit flat in the sun and rain, which is hard on any finish. The USDA Forest Products Laboratory's Wood Handbook notes that film-forming finishes on decks often do not last any longer than penetrating stains,^[1] and they are much harder to redo.

Penetrating stains soak into the wood. Penetrating finishes do not form a film, so they cannot crack or flake;^[1] they wear away slowly, and refinishing means cleaning the deck and brushing on another coat. Oil-based semitransparent stains carry pigment, and in general more pigment means more protection from the sun.^[1]

Solid-color stains and paint hide the grain and look like paint. Solid-color stains form a film like paint, and manufacturers do not generally recommend them for decks,^[1] because they wear through underfoot and peel.

Watch the label. Some products sold as semitransparent are not truly penetrating. The handbook warns that waterborne semitransparent stains often form a thin film and can fail by peeling and flaking.^[1] Test any product on a hidden board first. If it dries with a sheen, it is forming a film^[1] and is likely to peel.

Before you start

Look at the deck itself. Staining is surface work, but it is a good moment to check the structure. Fairfax County's building official advises homeowners to evaluate your deck annually and have it inspected regularly by a licensed contractor,^[4] and if the connections or the wood look wrong, to consider staying off your deck until a professional inspects it.^[4]

Know what the wood is. If your deck was built before 2004 and is not cedar or redwood, it was most likely built with wood pressure-treated with chromated copper arsenate (CCA).^[2] For those decks, the U.S. Consumer Product Safety Commission advises you to avoid sanding or power washing CCA-treated wood, and not to use harsh cleaners such as bleach, sodium hydroxide, sodium percarbonate, oxalic acid or citric acid on it.^[2] Staining is still worth doing: the EPA says applying a penetrating stain on a regular basis may reduce the leaching of chemicals from an older CCA deck.^[3]

New wood needs to dry. Treated lumber is sometimes still soaking wet when it is delivered and built into a deck.^[1] It feels unusually heavy, and water comes out if you squeeze a scrap. Nothing will coat wet wood well,^[1] so wait for it to dry.

Old film finishes have to come off first. Do not put an oil-based semitransparent stain over a film-forming finish.^[1] If the deck was painted or has a solid-color stain, see why deck stain peels for the choices.

Clean the deck

Sweep, clear the gaps between boards, and look for mildew, the black or gray growth that collects in shady, damp spots. To tell mildew from dirt, put a drop or two of household bleach on a dark spot. Mildew usually bleaches out in a few seconds; a spot that does not is probably dirt, iron stain or extractives from the wood.^[1]

On a deck that is not CCA-treated, use a commercial deck cleaner or a dilute bleach solution. One part bleach to five parts water should be enough, and you should never need a mix stronger than one part bleach to three parts water.^[1] Use powdered detergent, not liquid, which may contain ingredients that react with bleach to give toxic fumes, and never mix bleach with ammonia or a cleaner that contains it.^[1] Scrub with a stiff brush and rinse well. If you use a power washer, keep the pressure low to avoid damaging the wood.^[1] Oxygen bleaches, the sodium percarbonate in many deck cleaners, are likely to do less damage to the wood than chlorine bleach.^[1]

Do not use steel wool or a steel wire brush on cedar, redwood or oak:^[1] iron left in the wood reacts with its tannins and leaves blue-black stains.^[1]

Put the stain on

A brush is the best way to put stain on a deck; a roller or sprayer can put too much stain on a horizontal surface.^[1] Stir the can often so the pigment does not settle.

Stain two or three boards at a time and keep a wet edge,^[1] working each board from one end to the other. Stopping halfway along a board leaves a lap mark where wet stain overlaps dry. The handbook's advice: "If possible, work in the shade to slow drying."^[1] Do the railings first so drips land on unstained boards.

Put on only what the wood will take. In the handbook's words, "If the coating does not soak in, you have applied too much."^[1] If the stain has not soaked in within an hour, wipe off the excess with a cloth, sponge or brush lightly wetted with stain.^[1] Where stain fails to soak in it leaves a shiny film, which can peel if it is thick enough.^[1]

On rough or weathered boards, a second coat goes on while the first is still wet; smooth, new wood is usually finished with one coat.^[1] Follow the can for drying time before the deck takes foot traffic or furniture.

Clean up safely

Rags, sponges and paper towels wet with oil-based stain can catch fire on their own.^[1] To prevent that, immerse them in water and seal them in a water-filled, airtight metal container right after use.^[1] For leftover stain, check your county's household hazardous waste rules; Fairfax County's household hazardous waste program takes stains, paint thinner, mineral spirits and wood preservers from county residents free of charge.^[6]

Stop and call a pro if

• Boards, joists or posts are soft, rotted or badly split, railings wobble, or the deck is pulling away from the house. That is a repair before it is a finish job.
• The deck has peeling paint or solid-color stain that would need stripping, especially on a house built before 1978: the EPA notes that any renovation, repair or painting project in a pre-1978 home that has lead-based paint can easily create dangerous lead dust.^[5]
• The deck is high off the ground, and reaching the railings or the outside of the rim means working from a ladder.

For the time and money side, see whether to stain it yourself or hire someone and how often a deck needs it. You can also browse deck staining and sealing businesses, look up exterior pros around Blacksburg, or read more exterior answers. When you would rather have it done, describe your deck staining job once and local businesses can quote it.