there is a great spray called ''green clean'', i just used some out the back of my rug cleaning 'centre' . Spray it on and leave for two days then hose/pressure wash off. Should last for the whole year, can last a lot longer tho. It the kind of thing you use if your promising green free paths all year round to your customers. you can get it sent to you from a company up north called Killis Kleaners. Is good for patios walls and decking