Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2005

Primer for Painting Aluminum Aircraft--Strontium Chromate vs. Zinc Chromate

Q. I have a customer who is building a homebuilt alclad aluminum aircraft and has asked whether zinc chromate or zinc oxide primer would be better?

He said he was told that zinc chromate primer will be phased out because of it being so toxic.

A. Thanks for your mail. Zinc chromate is better on aluminum than zinc oxide, but the surface preparation is critical. The air force and aerospace industry use strontium chromate primers, and it is not likely to be phased out anytime soon. However, chromates are toxic and painters MUST wear the appropriate respirators. Once the primer has been applied the dry coating film is not toxic until or unless it is sanded off at some time in the future.

An epoxy strontium chromate, MIL-P-23377 is the most common primer used for aircraft, but this type of primer is generally not available in hardware stores and must be purchased from industrial paint stores or directly from the paint vendors.

Best wishes,

Ron Joseph