MetalPro Grey Primer and MetalPro Black Primer are recommended on rusted ferrous metals after using MetalPro Rust Converter to ensure proper adhesion of the topcoat and provide additional protection against future rusting. Grey Primer is a rust inhibitive primer with rust-inhibiting pigments that penetrate the surface for long-lasting protection, while the neutral grey color is compatible with a range of topcoat colors. Black Primer has the same formula and protection with a black color ideal for darker topcoats.