A high concentration of zinc gives these primers excellent corrosion resistance for protecting steel—when exposed to moisture and chemicals, the zinc rusts before the underlying steel can. They’re often used with structural steel to prepare the surface for paint while forming a protective layer.

Polyurethane primers can be applied in environments with high humidity. They allow underlying moisture to escape while preventing additional water from getting in. Surface must be visibly dry and free of frost and ice. Apply with a brush, roller, or sprayer.