Originally published July 1997
What is a sealant and what is a primer gets pretty intertwined. You sometimes have to "go with what you can get." I try to make a distinction based on the purpose. If it is primarily to seal, it is a sealant. If the material is used to improved painting, it is a primer.
The grouping of various purposes are listed below. This is a portion of data sheet Table of Contents from Courtauld Aerospace publications. At least at my company, the perception is that if they don't have a sealant or a primer for a given purpose, then no one does. (Each Category may have 25 or more specific formulations for sale.)
Epoxies were a big boon in industry over Zinc Chromate when they became readily available. Then EPA was formed and they were really needed. Polyurethanes are even better and their cost is less of a factor now.
For a primer, I would go with a urethane compatible epoxy. At least with a low VOC epoxy primer. I don't know how this fits in with the Stits Process but I bet someone else can tell you.
Don't do like one of my idols, Steve Whitman, and fall into the "I have always done it this way" trap. I will always remember Steve Whitman for his accomplishments and how he help me dream aviation, but I am sure that he will have saved countless peoples' lives at the expense of his and his wife's by his one "mistake."
(The folks at Poly Fiber have a wide variety of primers available for your use. Stits primers are used exclusively at the Flying Snake Ranch. Poly Fiber has also developed a 4-step Composite Finishing Process that is completely NON-HAZMAT. It sounds really good for you plastic airplane buffs. George Gennuso owes The Leading Edge a report on his experiences with this system. Rumor has it that Poly Fiber will soon be releasing a NON-HAZMAT primer and fabric finishing system, but we won't see it until it has been sufficiently beta tested. Check it all out at http://www.polyfiber.com or call them at 800-362-3490 and ask for the free info pack. Or, shucks, just cruise down to Flabob and visit them at the plant. You might want to call and warn them first. Wear your distinctive Chapter 1000 Project Police Tactical Assault Force T-shirt for extra brownie points. -- ed)
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 -- 22 December 1997