Doing job next week for a truck transfer station. Theres a 30' high wall where the trucks park near a garage and theres a white painted wall that has turned black from the diesel smoke exhaust. I was thinking of x-jetting sodium hydroxide solution to loosen it but Im afraid of the paint. I know I could just hot water blast it but Im trying to see if I can avoid a lift. I am mostly a residential contractor so forgive me for my lack commercial knowledge. Any feedback would be helpful.