hi
i've got to clean a painted (concrete?) flat roof that's covered in various types of algae and lichen as well as very dirty. i would attack it with some sodium hypochlorite but the roof is surrounded by some fancy ornate leadwork and i think i read somewhere that sodium hypochlorite and lead don't like each other? whatever chemical i use will come into contact with the lead anyone got any suggestions on what would be safe to use virasol, g101, hypo? as it's going to need something more than just water.
any advice appreciated