I'd recommend Jeyes fluid, diluted as per the instructions on the bottle. Spray the area to be treated with the dilute mixture using a watering can with a fine rose. Allow to act for about half an hour, then rinse off with cold water and a yard brush. I use it to treat a north facing driveway and it helps keep it moss free. I love the smell of it as well! It works well on timber decks as well.