TOPCOAT MP-300 primer can be used to brush-treat small scattered areas of rust, or it can be sprayed over areas of widespread rust. It is non-flammable, VOC compliant, and cleans up with water. This is a light blue, acrylic water-based, industrial primer/rust inhibitor that must be applied to any areas of rust before TOPCOAT Flashing Brush Grade or TOPCOAT Membrane can be applied. TOPCOAT MP-300 Primer is designed for use on metal and should be applied over any areas of rust that remain on the substrate after pressure washing. Heavy, flaking rust and scale must be removed by scraping, wire brushing, or grit blasting, followed by power washing with water.