The majority of patio cleaners can simply be applied and left to do their work, and the next rainfall will take care of the rest. The only situation where you might need a pressure washer is if the solution is strong and you don't like the smell lingering (or the idea of your pets walking over it). Otherwise, if there's a lot of algae build up it might be quicker to initially remove this with a pressure washer before using a solution. You can always do two applications of the cleaner for better results. Other than that, an application with a brush or stiff broom is enough for most situations.