Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2003

Zinc-Rich Primer vs. Zinc Metal Spray

Q. We are building a steel bridge near the sea shore, (a C5 environment), and we want a long-life durability over 20 years. The coating system will be zinc primer + epoxy middle coat and polyurathane top coat, but we don't know which is better to use zinc rich coat or zinc spray coating?

A. Both the zinc-rich primer and the zinc metal spray should give you much the same corrosion protection, but the zinc metal spray (using molten zinc wire) is probably much more expensive and slower to apply. Either way, you will need excellent surface preparation (white metal, or near-white metal) and a certain degree of roughness in the abrasive blast profile. To the best of my knowledge the Golden Gate Bridge in San Francisco, which is exposed to a very corrosive marine environmental has a zinc-rich primer.