I borrowed a friend's gasoline-powered pressure washer to clean the mossy-covered bricks in my back yard. The machine was noisy and smelly and I had to keep refilling the tank, but I loved the results, so I bought an electric pressure washer (the Sun Joe SPX3200). It's superior in every way to the gasoline-powered washer. It's quiet and goes into idle mode when you release the trigger. It has five different nozzles, including one to spray soap. If you have never seen what a pressure washer can do, this subreddit will make you a true believer.