Originally published April 1998
MIL-C-8507 (Reference 1) provides instructions for the application of wash primer pretreatment coating compound, Specification MIL-C-8514 (Reference 2) prior to application of a primer. The Appendix is a proverbial textbook on how to clean and pretreat metals prior to priming. With all the new formulations of cleaners and primers, it looks like the detailed instructions made it technically out of date and led to its cancellation.
MIL-C-8514 covers one type and grade of pretreatment coating for use on clean metal surfaces of all types as a treatment prior to application of the coating system.
"The pretreatment coating covered by this specification is intended to be used as a treatment on aircraft metals, prior to the application of any primer, and is not intended as a permanent protective coating in itself. The function of this pretreatment coating is to upgrade the adhesion of the subsequently applied aircraft primer."
"Topcoating directly with lacquer, without prime is prohibited, since poor adhesion or poor corrosion resistance or both will result."
The above quote from Reference 2 indicates that "Wash Primers" were intended to provide excellent adhesion for primers and not for paint or for corrosion protection.
My opinion is that there is a very definite place for wash primers in industrial paint applications where low cost is important and corrosion is not the primary concern. Examples such as metal signs and control boxes for oil field equipment. Likewise, my opinion is that wash primers just add one more step in aircraft coatings because of the need for corrosion resistant systems prior to paint.
Thanks to Ray Lusby for sharing his experience with the contrasting requirements of the industrial and the aircraft paint systems. He has also used wash primers on oil field equipment and chem film and primer on airplanes. He contributed both to this article and last month's article.
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 12 April 1999