Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2006

Painting Over Zinc Plating

Q. I have read several articles about duplex systems (paint over galvanized steel). I am looking for information about what types of paints are compatible with zinc plating (I assume painting over zinc plating is similar to painting over galvanized zinc)?

A. Generally you can use the same paints on zinc plating as you do when you paint over galvanizing. I strongly suggest that you first pretreat the surface with either an iron or zinc phosphate process. Alternatively, you can apply a vinyl butyral wash primer, but the phosphating process is generally considered to be preferable to the wash primer approach. Moreover, the VOC content of wash primers is high (often >650 g/L) and many state agencies have outlawed this type of product.

Alkyd and alkyd modified coatings should not be used in direct contact with the zinc as they tend to saponify upon contact with zinc in humid environments. On the other hand, an epoxy primer followed by any of the following topcoat; alkyd, acrylic, epoxy or polyurethane, should perform well.

Select the appropriate coating system based on the type of exposure to which the painted product will be exposed.

Best wishes,

Ron Joseph