I have to pressure wash some 5000sq of exterior metal that has been painted 6-7 years ago before I can repaint it.
I rented a 3500 psi power wash machine and I get as close as 1 inch to the metal but it still doesn't get all the dirt and crap off. Only cleans about 80%.
I get all wet and my eyes dirty when I finish only a few feet. I can't even use protection glasses cuz they get dirty and foggy immediately.