Zinc-rich primer

A zinc-rich primer is an anti-corrosion primer loaded with metallic zinc dust that protects steel by galvanic (sacrificial) action: the zinc corrodes preferentially and holds the steel cathodic at any coating breaks. Two families exist: inorganic zinc silicate and organic (epoxy) zinc-rich. To stay conductive the dry film must carry a high zinc content, commonly above about 80% zinc by weight in the dry film for inorganic types. It needs a clean blasted substrate, typically Sa 2.5 to Sa 3, with a defined surface profile. Shop primers (pre-construction primers) are thin zinc or zinc-phosphate films applied right after blasting to protect plate through fabrication.