Ask the Expert Question-and-Answer Archive

by Ron Joseph

March, 2009

Zinc Dust Primers on Machined Surfaces

Q. I am writing a paint specification for a wind turbine. Components of the turbine are made from cast, machined, forged, and fabricated steel, are all these surfaces suitable for use of a zinc rich primer? Do any of these substrates requires a specific type of primer? I have read that zinc rich promers are not ok for machined surfaces, why is this?

A. Zinc-rich primers are heavily filled with zinc powder and there is very little resin to hold the zinc particles together. Therefore, you must abrasive blast the substrate to provide enough of a profile to enable the primer to adhere. Usually, one machines a surface to a fine tolerance; hence, you would not want to abrasive blast it and destroy the machined surface, warp it or change its dimensions in any way. On the other hand, unless you have other reasons, you can abrasive blast cast, forged and fabricated steel. With regard to fabricated steel, you would not want to abrasive blast thin, or relatively thin sheets since you might distort or even penetrate them.

Immediately after applying the zinc-rich primer it is common to apply an epoxy primer followed by a decorative or protective top coat. Typical top coats include acrylics and polyurethanes. I strongly suggest that you apply the non-zinc primer within a day or two after applying the zinc-rich primer.

Finally, I suggest you find a well qualified and experienced painter to apply the zinc-rich primer. Because there is so little resin in the formulation, the painter must know how to properly mix and apply it. An inexperienced painted might apply it too dry.

Regards,

Ron Joseph