Masterchem 43125 Hammerite Rust Cap Rust Preventative Paint Hammered Dark Blue 1 Qt Can be applied directly over firm, rusty surfaces For use on metal substrates For previously painted surfaces, apply hammerite rust cap enamel finish to a small area first to check adhesion and test for lifting or cracking Formulated for interior and exterior use Aluminum and galvanized surfaces require a prime coat of hammerite rust cap 48300 galvanized and aluminum primer