You often hear different views on pressure washing roofs, some say it's fine if you are careful, some say it should never be done. I guess roof condition comes into it from a starting point, however from an actual damage to the roof point of view, what's the worst thing that has happened on a roof you power washed and what was the end result? I am going to take tentative steps to clean my own roof which is 1970's concrete tiles to see how I get on.