On a steel bridge in Central New Jersey used for testing 47 various coating systems, only 3 of the 12 epoxymastic type systems tested graded at 8 or above according to ASTM D610 after eight years of exposure. In the same test, 10 of the 14 systems tested with zinc-rich primers scored 8 or better, and 13 of 14 scored 7 or better.4 (ASTM D610 “8" = 0.1% rust; “7" = 0.3% rust)
In marine exposure testing, epoxymastic coatings from various vendors showed significant underfilm corrosion from intentional defects after as little as 18-months. Similar underfilm corrosion results were found on SSPC SP-5 test panels exposed to laboratory accelerated tests.5, 6
In the FHWA-sponsored “PACE” study, the epoxy primer coating systems tested showed poor performance compared to other generic types of coatings evaluated under similar conditions. This study showed epoxy primer systems failing due to underfilm corrosion.