Check, clean and seal your deck
A five-second water test tells you whether the finish is still working. A yearly structural check tells you whether the deck is.
Step by step
If the deck is new pressure-treated wood, wait at least 30 days before testing or sealing. Some experts say two to three months.
Sprinkle water on a few high-sun, high-traffic spots. If it soaks in and darkens the wood within about five seconds, it's time to treat. If it beads, the finish is still working. On new wood, beading can just mean the wood is still wet.
Do a yearly structural check before you finish the deck. Make sure the ledger board is bolted to the house, not just nailed, and that the flashing above it is intact.
Push a screwdriver into joists, posts and boards. If it sinks in ¼ to ½ inch or the wood feels spongy, there may be rot. Tighten loose fasteners and replace corroded ones, and make sure railings and stairs don't sway.
Clean with a deck cleaner and rinse. Avoid aggressive power washing that tears up the wood.
Let the wood dry for at least 48 hours after cleaning or rain.
On walking surfaces, use a penetrating finish rather than paint or solid stain, which tend to peel.
Work in small sections along the full length of the boards, keep a wet edge, and back-brush any puddles. More is not better.
Clear water repellents typically last about a year. Pigmented semi-transparent finishes last longer.
Safety first. Never mix bleach with cleaners that contain ammonia, because together they make a toxic gas. Follow the label's weather limits. Many products call for about 50–90°F with no rain for 24 hours. If the structural check turns up rot, a loose ledger or a wobbly railing, have a deck professional look before anyone uses the deck.