I have been reading OA and siding threads and searching for a bit but mostly find references to OA on concrete and vinyl and really not much on painted surface. Same elderly family friend as my other topic about black patio ceiling. They have serious rust stains from well water fed sprinklers on what appears to be (ATB) painted wood siding. Planning OA/H20 in a pump sprayer to remove rust from their siding. Now I am questioning the ability to remove the rust without excess paint damage using OA on their yellow painted siding.