RUST DEFENDER Hi-Build Polyester Primer is a one step system that primes, fills and seals bare metal, body filler, wood, aluminum, or fiberglass surfaces to accept any type of paint without concern about penetration of solvents or moisture. It has excellent resistance to heat, solvent attack, water, and salt. Non-shrinking and easy sanding, either wet or dry, it provides an excellent barrier between cured body filler and topcoats. Clear Coat/Color Coat paint systems are protected from the body filler when using this product.