Powdered laundry detergent and hot water is usually enough to clean a moderately dirty deck. However, if the deck has seen better days, a chemical wood brightener along with a pressure washing may be what's needed. Once clean, we suggest that you moisturize the wood with an oil-base stain or wood preservative. Whatever you do don't buy anything with wax in it. When you wet a wood surface that has been sealed with wax the water will bead beautifully. Unfortunately, that beautiful coat of wax doesn't penetrate as far beneath the surface as oil does. Worst of all wax evaporates far more rapidly than oil – about 2- to 3-times as fast – a bad thing. A good wood preservative also incorporates chemicals that prevent damage by ultraviolet rays of the sun and from attack by mildew.