With minimal prep, Steel Curtain & Quik Tann easily converts rust to a primed, paintable surface in less than three hours. Environmentally friendly and less than 3% acid, won't weaken the metal or irritate your skin. It's finished working when the areas of rust turn black. Don't worry about over spray, won't harm fiberglass, rubber or painted surfaces. Less residue, mean less labor and better primer / paint adhesion. Steel Curtain is specially formulated for high humidity, acid, environments, particularly where bacteria, mold and fungi are present.