Rust is caused by moisture coming in contact with metal, which causes a chemical action called oxidation. All paints provide a measure of protection for a while, but since they are eventually softened and weakened by moisture, it is only a matter of time before moisture penetrates the painted surface and attacks the metal below. All of the so-called rust preventive paints on the market (except POR-15 Rust Preventive Coating) are weakened by exposure to moisture. POR-15 Rust Preventive Coating is strengthened by exposure to moisture. Notice the hardness of the POR-15 coating. It doesn't chip, crack, or peel like ordinary paints do, and its hardness will resist the wear and tear of every day life.Rust conversion products claim to change the chemical nature of rust and convert it to a more stable element that won't rust again. History of the failure of these products is well documented; most simply don't work for more than a few months at best, and they are subject to the same chipping and cracking that occurs with ordinary rust coatings.POR-15 Rust Preventive Coating works because it chemically bonds to rusted metal and forms a rock- hard, non-porous coating that won't crack, chip, or peel. It keeps moisture away from metal with a coating that is strengthened by continued exposure to moisture.