POR-15 is a paint-like substance that acts as a total rust inhibitor and metal filler. POR-15 chemically bonds to rusted steel to form a rock-hard, non-porous coating that won't crack chip or peel. It works by isolating metal from air and moisture. Unlike many other substances, POR-15 is actually strengthened by exposure to moisture. Due to its strength and hardness, POR-15 is perfect for frames, axles and under fenders because stones and rocks WILL NOT chip it. Its consistency is similar to paint. One quart covers 96 square feet, which is more than enough for an average frame.