I have lost track of how many times people told me that and said THAT IS CRAZY MAN! and now they are doing it as well:B but after 3 5er's and 10 years of 3 times a year of doing the Electric power washer with no damage ya think I would have done damage by now AND I do the top of the Awning while I am up there Again the key is ELECTRIC power washer it does not even come close to taking caulking off or lifting the rubber roof off I would NOT use a gas 4-5K P.S I. washer That would be Crazy ,my Neighbor has been doing the same thing for years like I have if other folks want to spend a few hours scrubbing with cleaners and brushes have at it I got better things to do,believe me try it and you will never go back to Scrubbing and love the results:)