Corrosion Resistance

Testing focused on LHE Zinc-Nickel (Zn-Ni) plated high-strength steel substrates — representing the multi-layer protective system used on demanding industrial and structural steel components in corrosion-critical applications. Both white gloss and grey semi-gloss urethane topcoat variants were assessed, with and without Gentoo treatment.

Test Configuration

Accelerated ASTM B117 salt fog corrosion testing was performed on LHE Zn-Ni plated 4130 high-strength steel (HSS) painted panels. The panels were primed with MIL-PRF-85582 Class N chrome-free epoxy primer and topcoated with either:

• White gloss urethane: CA8201/F17925 — MIL-PRF-85285 Type I Class H, or
• Grey semi-gloss urethane: CA8211/F3673 — MIL-PRF-85285E Type I.

Control panels included the primer and topcoats only, with no Gentoo treatment. Gentoo was applied to selected control panels as the additional protective treatment. All panels were "X" scribed per MIL-PRF-32239 to simulate mechanical surface damage exposing bare metal — the most aggressive corrosion initiation condition. Panels were placed in ASTM B117 salt fog with images recorded every 500 hours and scribe corrosion rated per ASTM D1654.

Results

Significant red rust corrosion product appeared on all panels — both treated and untreated — within the first 500 hours of ASTM B117 salt fog exposure. This is expected behaviour: ASTM B117 is an accelerated test specifically designed to drive rapid corrosion development, not a replication of real-world timescales.

The critical comparative measurement is scribe corrosion creep — the rate at which corrosion migrates laterally from the scribed line into the surrounding coated area. This measurement, rated per ASTM D1654, directly indicates how effectively the coating system limits corrosion spread from a damage point.

For both the white gloss and grey semi-gloss topcoat variants, Gentoo treatment significantly reduced scribe corrosion creep versus the control panels. The reduction in corrosion creep is consistent across both topcoat types, confirming that the Gentoo benefit is attributable to the coating itself rather than to any specific interaction with one paint formulation.