Ask the Expert Question-and-Answer Archive

by Ron Joseph

March, 2008

Zinc Chromate Primer and Topcoat Compatibility

Q: I understand that zinc chromate primers are difficult to come by but I have located some that are alkyd enamel based. What types of topcoats are not compatible with this primer? (lacquer, epoxy, oil based enamel,etc).

I intend to use is paint in a marine application on aluminum.

A:Alkyd primers can be top coated with alkyd top coats. You should not apply any top coat in which the solvents are too strong. For instance, if you apply an epoxy or polyurethane over the alkyd, the solvents in these coatings will lift the primer, much like a paint remover lifts a coating. Mineral spirits is a mixture of weak solvents and can be applied over an alkyd. Also, most waterborne paints can probably be applied.

Before making your final selection, I suggest that you first conduct some tests.

By the way, alkyds are not the best choice for protecting aluminum from marine environments. If I were painting an aluminum boat I would probably select a marine grade epoxy and polyurethane system.

Regards,

Ron Joseph