You can wash a deck by hand or, for a large deck, using a pressure washer.

Using a stiff fiber bristle brush on a broom-type handle, thoroughly scrub the surface with a sudsy solution of water and laundry detergent. Rinse with clear water and allow to dry.

If you decide to use a pressure washer, get one that delivers 1,200 psi (pounds per square inch) of pressure or less and has a spray nozzle that fans an arc of about 25 to 40 degrees.

Be careful: the powerful spray can erode soft wood grain. Allow the deck to dry for several days before applying any type of finish. See more about properly using a pressure washer.