POR-15 Rust Preventive Coating is the Only Product that REALLY Stops Rust Permanently! POR-15 Rust Preventive Coating is designed for application directly on prepped rusted, sandblasted, and seasoned metal surfaces. It dries to a rock-hard, non-porous finish that won’t chip, crack, or peel, and it prevents rust from recurring by protecting metal from further exposure to moisture. POR-15 Rust Preventive Coating is sensitive to UV light and must be top coated when prolonged exposure to sunlight is possible. Top coating is not required for areas not exposed to sunlight.