Before you start, remove everything from the deck including furniture and potted plants. Loosely cover any delicate or fragile ground plants adjacent to the deck with tarps or drop cloths. Don't use plastic sheeting on shrubs and plants. It can create a deadly "greenhouse effect" and harm your plants. Remove drop cloths from your foliage as soon as your project is complete so they don't suffocate. Sweep off loose debris with a broom and clean between the cracks using a slender stick or tool. Repair damaged boards and hammer in popped-up nails.
Use a garden hose or a pressure washer to spray the surface of the deck, forcing away dirt, dust, oil and grease. This will also help remove the top layer of previous waterproofing. Begin at one end of the deck and continue until you have rinsed the entire surface and removed as much dirt as possible. If you use a pressure washer, keep the pressure set to less than 1,000 pounds per square inch and leave a few feet between the spray nozzle and the deck to avoid damaging the wood. Set it to spray a fan of water so it pushes dirt and debris away faster. Spray between the deck boards to eliminate any remaining debris. Use a pole sander or orbital sander with medium-grit sandpaper to smooth down any splintered areas and to remove remnants of the previous layer of sealant. Starting with as clean a surface as possible will help the new coat of sealant set in and provide a better level of protection.
When using a pressure washer, wear safety glasses to protect your eyes from splashing water and debris.
Cleaning your deck at least once a year helps it last longer and look better while maintaining the integrity of the wood. And when you're planning on sealing or refinishing your deck, you'll have to clean it first. Deck cleaning products are available in a variety of types and strengths. Some offer a special chlorine bleach formula for eliminating mold, mildew and algae. However, chlorine bleach formulas may require more frequent cleanings. Consider using a non-chlorine bleach cleaner instead, such as Woodsman® Premium Wood Cleaner.
The best outdoor temperature for cleaning and treating your deck is between 50 and 90 degrees Fahrenheit.
Make sure your deck is compatible with the cleaner you choose, especially, if your deck is made of soft wood like redwood or cedar. Check the manufacturer's instructions to see whether you should start with a dry or wet deck. Try to clean on a calm day to keep wind from blowing the cleaning agent around the yard. Use a deck stain applicator to apply the cleaner to the entire deck. While applying, be careful not to allow the cleaner to puddle anywhere on your deck to assure an even appearance.
Scrub tough areas with a stiff brush or a broom. Don't use wire brushes as wire bristles can break off into the wood and cause rust spots. Follow the product's instructions regarding how long to let the cleaner soak into the wood, usually about 10 to 15 minutes. After the cleaner has been allowed to soak, rinse the deck thoroughly with a hose.
Cleaners contain bleaching agents, so wear protective clothing, safety goggles and rubber gloves.
After cleaning your deck, let it dry for at least 24 hours.