Sunnyside Ready-To-Use deck and fence wash cleans and removes dirt, mildew, algae and fungus stains from unpainted exterior wooden surfaces. It restores the appearance of weathered wood and is also effective in cleaning composite decks. Deck Wash is completely biodegradable, and contains no petroleum distillates, acids, or phosphates. 1 gallon will cover 150 to 250 Sq. Ft.