Ref #17: Use a wood deck cleaner if the deck is wood. Use a composite deck cleaner if the deck is made from a composite material. The posts and other vertical boards will not be made from composite material, but they become dirty much less often. Chlorine bleach (laundry bleach) should never be used because it damages the wood. Also, it does not remove dirt well. It just gives the appearance of cleaning well because it bleaches the wood to a lighter color.