This specification covers highly pigmented primers that contain zinc dust as the major pigment component (minimum 65% by weight in the dry film) and are defined by their ability to protect ferrous substrates. Individual products meeting minimum performance requirements of this standard may vary in formulation, raw materials, and application characteristics. SSPC Paint 20 is a performance standard for inorganic or organic zinc-rich coatings that includes options for specifying higher zinc loading levels in the dry coating film.