Met’l Clad 449 Rust Inhibitive Primer is an excellent rust preventative primer for iron and steel surfaces. It contains Barium Metaborate, a non-toxic, rust inhibitive pigment. It also contains Mica, a pigment that forms a protective layer that bridges micro pores in the paint film, preventing moisture and air from reaching the metal surface. These pigments are ground into Alkyd Resins and Linseed Oil which penetrate rusted surfaces to stop and prevent corrosion. This product is effective on all ferrous metal surfaces, interior or exterior.