A pressure-treated deck will require cleaning once or twice per year, depending on location and climate. Wood decks are prone to mold and even moss growth. Organic material (like autumn leaves) will also mar the deck surface if allowed to accumulate and sit on the deck. Cleaning a pressure-treated deck on a regular basis is an essential part of preserving the wood.
Remove all deck furniture, planters, grills and other items from the deck.
Sweep the deck to remove sand, leaves and other debris.
Don protective eyewear to protect your eyes from debris that may become airborne during the power washing process.
Attach a garden hose to a power washer, turn on the water supply and then turn on the power washer.
Power wash the deck, using extreme caution to avoid damaging the wood surface. The end of the power-washer wand should be at least 18 inches away from the deck surface. You may skip this step if your deck is fairly clean (that is, free of mold and major stains.)
Fill a bucket with water and add oxygen bleach, such as OxyClean, to the water. The recommended amount for use as a surface cleaner will vary depending upon the precise product.
Don rubber gloves to protect your hands from the chemicals.
Pour a bit of the water and bleach solution on the deck surface and, using circular motions, scrub the deck wood with your scrub brush. Repeat until the entire deck has been cleaned.
Detach the garden hose from the power washer and rinse the deck using just the hose.
Allow the deck to dry for 24 hours.
Don a face mask and rubber gloves.
Brush on a coat of deck sealer to preserve the wood and to prevent stain absorption. This step is particularly important if you've power washed the deck, as you'll remove some of the existing deck sealer during the power washing process.