Frequently Asked Questions

What is the difference between a zinc-rich epoxy primer and a red oxide primer for steel corrosion protection?

Red oxide primers (iron oxide in alkyd or modified alkyd binder) provide only barrier protection — they slow corrosion by reducing the rate of oxygen and moisture reaching the steel, but they do not provide galvanic protection. If the primer coat is scratched or damaged, corrosion begins immediately at the bare steel. Zinc-rich epoxy primers (such as Nitozinc Primer) provide both barrier protection and galvanic protection — the zinc sacrificially protects the steel even where the primer is damaged, preventing corrosion from spreading from a scratch. Zinc-rich primers in epoxy binders are also tougher, harder, and more chemically resistant than alkyd red oxide primers, giving much longer service life in aggressive environments. For structural steel in industrial, coastal, or other aggressive environments, zinc-rich epoxy primers are the specification-grade choice.

Does Nitozinc Primer require any special surface preparation of the steel?

Yes. Zinc-rich primers require the highest level of surface preparation to achieve effective galvanic protection. The steel surface must be blast-cleaned to Sa 2.5 (near-white blast) as defined in ISO 8501-1. This level of blast cleaning removes all mill scale, rust, oil, and contamination and produces a uniform near-white metallic surface with a surface profile (roughness) of Rz 50 to 70 microns, which provides the mechanical key for the primer adhesion. Inferior surface preparation (such as hand tool cleaning or light blast cleaning) significantly reduces the service life of the zinc-rich primer and the overall coating system. The primer should be applied as soon as possible after blast cleaning (within 4 hours) before the fresh steel surface begins to flash rust.

Can Nitozinc Primer be applied to corroded or rusty steel?

Nitozinc Primer requires blast-cleaned steel and cannot be applied over existing rust or corrosion products. The rust layer creates a weak boundary between the primer and the sound steel, and the galvanic mechanism requires direct electrical contact between the zinc particles in the primer and the steel substrate — rust (iron oxide) on the surface breaks this electrical continuity and eliminates the galvanic protection. For corroded steel, all rust must be removed by blast cleaning to Sa 2.5 before the primer can be applied. In cases where blast cleaning is not practical (such as in confined spaces or near electrical equipment), a moisture-tolerant surface-tolerant epoxy mastic primer compatible with less-than-ideal surface preparation may need to be considered as an alternative, but these products do not provide galvanic protection.