Water-seal products for pressure-treated wood surfaces like decks and gazebos need to be reapplied regularly. Before you do, however, you'll want to clean the surface first. A pressure washer is often necessary as well to effectively lift the kinds of stains that accumulate on outdoor wood decks. But how long do you have to wait after washing the deck before you can apply the sealer?
Why Reseal?
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Over time, waterproofing coatings break down due to weathering and your beautiful wood deck will begin to turn gray. A new coat of water seal will help protect the wood, resists mildew and discoloration and protect the wood's natural colors. But first you're going to want to clean off the gray filmy buildup.
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Cleaning the Deck
A variety of easy-to-use deck cleaning solutions can be sprayed on with a simple garden sprayer. You can also use a 1 to 4 solution of household bleach and let it sit for 15 to 30 minutes. Properly dilute it and to spray it on evenly to prevent spotting. Once the deck-cleaning solution has had time to loosen the mildew and stains, hit it with the pressure washer using smooth, even strokes. Don't get too close or you can make streaks and fuzz up the wood and leave marks. Rinse thoroughly.
Sealing
Most sealers can be applied to damp wood. Thompson's says that you can apply its water-seal product directly to "damp, freshly cleaned wood." Rinse the garden sprayer you used to apply the deck cleaner and use it to apply the water seal. Use smooth, even strokes. If you're worried about streaking or spots on the deck, buy water seal with stain in it. The stain is carried into the surface of the wood by the sealer and gives older, worn deck surfaces a nice, even finish.
Caution
Let the sealer dry before wetting the surface again. Don't apply on rainy days or during the hot part of the day in direct sunlight. Hot surfaces may interfere with the adherence of the water seal product.