Before beginning your deck refinishing project, check the weather forecast. You need four or five days of dry weather to clean and refinish the deck. You can clean your deck using soap and water, plus a garden hose or a power washer. After cleaning, allow the deck to dry thoroughly for a minimum of 24 hours. If the wood does not appear to be dry in that time frame, allow it to continue drying for up to two or three additional days.
Before beginning to clean your deck, remove all furniture, planters and outdoor items. Cover adjacent bushes and landscaping with a plastic or canvas tarp. Unless your deck is overly dirty, cleaning with soap and water and a garden hose is sufficient. Using the hard-spray nozzle of a garden hose, spray to remove debris from the surface and between the boards. Push out any remaining debris with a putty knife. Clean the deck with a soapy solution of laundry detergent and water. Apply the solution with a rag to small areas at a time. Scrub the boards, rails and posts with a stiff brush, scrubbing in the direction of the wood grain. Rinse the soap from the boards as you go with the hose.
For large decks, the use of a power washer simplifies your task. Rent a power washer from a local rental company. Use 1,200 psi of pressure and a nozzle with an arc of 25 to 40 degrees, holding the nozzle 6 inches from the surface. Spray with the grain of the wood. Wash the top rails and posts first, followed by the deck boards. Wear safety goggles when using a power washer as a precaution.
Some decks will accumulate stains or mildew that cannot be removed with soap and water alone. Bleach or acid-based solutions will help with more difficult cleaning. Always test the stronger products on an inconspicuous spot on your deck. To remove mildew, first clean the deck with a soapy solution. Then, apply a mixture of one part household bleach and four parts water to the deck. Rinse with a garden hose.
To remove other stains or to revitalize a weathered deck, prepare a solution of 4 oz. oxalic-acid crystals and 1 quart water mixed in a nonmetallic bucket. Apply the solution with a rag and scrub with a soft brush. Wear protective goggles and gloves when using acid solutions.
Commercial deck scrub products are available, as well, to clean stained finishes.