When to prime?

Simple question (I hope)...

Is there anything wrong with priming interior parts after assembly? Isn't the point to create a chemical/mechanical vapor barrier?

I've searched the forums and there's a lot of varied techniques for when primer is applied; before dimpling, after, etc but I don't see anything wrong with priming after riveting where you can. If the exterior will be painted, doesn't that bar water intrusion around seams and rivets?

Thoughts?

question

Do you want an airplane that will last 50 years or 100 years?

My C-172, built in 1957 is still flying...no primer, half it's life tied down outside...

Welcome to VAF!

Some of the structure you simply can't get to, one assembled.

I woul fit the parts, disassemble them, alumni prep and alodyne them at night. In the morning I would get a few minutes early and spray them. By the time I got home from work, they were ready for riveting.

In reply to your question, the answer is yes. The most important reason to prime is to create a chemical/vapour barrier as you call it at the interface between riveted parts. For example between the flanges of the fuselage bulkheads and the skin, and between the flanges of the empenage ribs and skin and between the flanges of the wing ribs and skin. If you prime after riveting you can create crevices where the moisture can seep and start corrosion.

The ribs and skins are alclad which does a very good job of resisting corrosion. The interior skins on my 1966 C-150 are fine, as I think are the joints between the flanges. But, yes, I primed all my parts on my RV-9A and I do want it to last 100 years.

primer

I did prime my -10 as I built it. My point was that even if you do not prime, the aircraft will likely outlive the builder. Hopefully, my -10 will be a family heirloom, being passed from generation to generation for the next 100 years...

Priming does take a substantial amount of time. If I built again, I would likely Alodine everything instead of using P60G2.