For heavy mould / algal growth apply undiluted. For lighter growth dilute with an equal amount of water. Apply Cuprinol Decking Cleaner generously by brush, spray or watering can (fitted with a rose). When spraying, use a coarse (airless) spray and avoid misting. Scrub affected area with a stiff brush, leave for a few minutes and then rinse off with water. Allow to dry fully before staining or oiling the deck. Cuprinol Decking Cleaner is not intended as a replacement for the regular treatment of your deck.