Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2003

Non-Chromate Primer for Composite and Aluminum Surfaces

Q. Are there any primers that can be used in bonding composites to aluminum that are water based and zinc and chromate free that still have equivalent corrosion resistance as zinc chromate solvent based primers?

A. As you probably know, zinc chromate is not a corrosion inhibitor for composites, but only for ferrous and nonferrous metals. Therefore, you require a primer for composites that provide excellent adhesion. In the case of aluminum you must properly prepare the surfaces prior to the application of the primer if you are to enjoy good adhesion and corrosion protection.

Having said that I'm not aware of any non-chromate-containing primer that provides equivalent corrosion protection to aluminum as does the chromate primers. If you are willing to settle for less, then Deft Inc. sells a waterborne epoxy primer to MIL-P-53030 which is used on aluminum surfaces of military (army) hardware, such as tanks, personnel carriers, etc. The air force does not use this primer, because they want to avoid the formation of filliform corrosion.

You should be able to use the Deft primer on both composites and aluminum surfaces, but I urge you to perform your own tested to confirm this recommendation.