Clean and seal a wood deck

Why decks need sealing

Bare wood soaks up rain and dries in the sun over and over, which makes it crack, split, cup and turn gray. A deck sealer or penetrating stain soaks into the surface and slows down how fast water gets in. Clear sealers protect against water; stains with pigment also block sunlight, which is what turns wood gray.

Sealer only soaks in well on wood that's clean and dry. Dirt, mildew and the gray layer of sun-damaged fibers block it, so cleaning is half the job. New pressure-treated wood also needs time to dry out before it will take a sealer; the product label says how long.

Signs a deck needs it

Let's fix it

1. Do the water testSprinkle a cup of water on a few boards in sun and in shade. If it beads up, the deck doesn't need sealing yet. If it soaks in within a few minutes and the wood darkens, it's time.
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2. Pick the weatherYou need two to three dry days in a row: one to clean, one or more for the wood to dry, and a dry day to seal with no rain for at least a day after. Check the temperature range on the sealer label, and avoid sealing in hot midday sun, which dries it before it soaks in.
   Done

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3. Prep the deckMove furniture, grills and planters off. Sweep it and clear the gaps between boards with a putty knife. Set popped nails and tighten loose screws. Cover nearby plants and siding with plastic, and wet the plants before and after cleaning.
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4. Clean itMix the deck cleaner as the label says, wet the deck, and spread the cleaner on a section at a time. Let it sit as directed without drying, then scrub along the grain with a stiff brush. Rinse well. If the cleaner label calls for a wood brightener afterward, apply it now. A pressure washer on low pressure with a wide fan tip held a foot or more away can help rinse, but up close it gouges and fuzzes the wood.
   Done

   Something went wrong?

   • The wood looks fuzzy after cleaning The pressure was too high or the tip too close. Lightly sand the fuzzy spots once it's dry.

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5. Let it dryGive the deck at least 48 hours of dry weather, or the time the sealer label requires. Sealer on damp wood stays on top, peels and blotches. If the wood still darkens when you sprinkle water on it the next day, it's still too wet.
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6. Apply the sealerStir it well; don't shake it. Start with the railings, then do the deck two or three boards at a time along their full length so you don't leave lap marks. Put on a thin, even coat with a pad, roller or brush, then brush back over it to work it in and spread any puddles. Most penetrating products need only one coat; follow the label if it calls for two.
   Done

   Something went wrong?

   • The sealer is sticky days later Too much was applied. Wipe off the excess with a rag and the cleanup product on the label.

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7. Let it cureKeep people and pets off for the time on the label, usually a day or two before furniture goes back. Spread oily rags flat outside to dry, or put them in a metal can filled with water and sealed, then dispose of them as your local rules allow.
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Watch it done

How to Clean and Restain a DeckBy This Old House on YouTube. Their method may vary a little from ours.

Watch on YouTube

If boards are damaged

If a board is cracked or soft, see the guide for replacing a deck board.

If the railing wobbles, see the guide for a wobbly deck railing.

Deck sealing questions