Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2003

Surface Preparation for Zinc-Rich Primer

Q. What is the recommended surface preparation in the repair of damaged galvanized surfaces if I am to use zinc rich primer?

A.If you intend to repair a galvanized steel surface by applying a truly

zinc rich primer, such as an inorganic zinc coating, then you will need to abrasive blast the damaged surface to a white metal finish. If the primer is heavily loaded with zinc, you must provide the surface with a profile of approximately 1.5 mils (38 microns). On the other hand, if you are using a primer that has a higher percentage of resin and less zinc, then you should also prepare the surface to a white metal finish, but you might not need the blast profile indicated above. Instead, you might be able to achieve this by sanding with a fine abrasive paper.

Bear in mind that for corrosion protection (cathodic protection) the zinc pigment particles MUST come into direct contact with the bare metal surface. If you apply the zinc rich primer over rust, scale, a previous coating, etc., the zinc will not be able to perform its cathodic protection function and you will not get a benefit.