Rust-Oleum Stops Rust Automotive Primer Spray. Light Gray. Fast-drying, rust-preventative formula can be top-coated or wet-sanded to an ultra-smooth finish in just 15 minutes. Suitable for use on a variety of materials both indoor and outdoor, except galvanized metals. Color works well under most automotive paints. Features a comfort tip with a wider finger pad, provides lasting protection and more.