To prime or not to prime, that is the question

Just starting my RV-12 project and have seen a number of airframes primed inside and out. I've also seen an equal number that were not. I know this is going to open a big can of worms, but... Building in Florida if that helps.

First, welcome to VAF. And good luck with your build. I'd love to come help you but you're a bit far away.

Next, search "primer" or "primer wars" and you'll probably have hours of reading. This is a subject on which there is no consensus and opinions run from one extreme to the other. You'll just have to do your research, weigh the pros and cons, and then make the decision that feels most comfortable to you.

Thank you. Found the "Search" menu and wow. Wars it is.

Try this thread

Try this thread. I was trying to make that decision about 5 months ago and posted this survey. I was surprised at the results. A lot more people doing rattle-can self etching primer than I expected based on the posts in the various primer war threads.

http://www.vansairforce.com/community/showthread.php?t=69126

In having to make that decision, someone asked me if my 65 year old Ercoupe was primed at the factory. Of course it was not, and it is just fine thank you without the extra weight. Since I would not live another 65 years I decided to not prime.

The most "common sensical" I read about priming...

... with a solid sense of humor on top:

http://home.hiwaay.net/~sbuc/journal/priming.html

And I note you live in Texas. My first RV was intended to live in California near the coast, and is primed throughout. Now I live in Arizona, so the factor has changed and the -10 gets no primer. There are other factors to consider, too, like how well it will be maintained, will it be hangared or not, and so on. I don't think anyone's simple yea/nay response will work for another without some consideration of their own circumstances. The original poster lives in an area where even when the environment is not positively marine it is still humid. I might suggest not merely priming but also using a herbicide to keep the mold down. (I used to live in Hattiesburg, MS; I know what humidity can do.)

One thing I've seldom seen mentioned, because I think some people ask this question hoping to avoid having to do any priming tasks during construction, is that even if you choose not to prime alclad, you will still be doing some priming. Angle and bar stock is not clad and must be primed. In places you will remove the cladding (for example, if you bevel the wing skins for a transition) and will need to prime at least in that area. And I prime the thicker stock just because so much unclad edge is exposed. So the question now moves to phase II of the wars: what primer/method to use.

"Here's your rifle and helmet. The front lines are thataway."

I'll note that we primed most of the inside of 331RV with SEM Self-etching primer. I now think we wasted our time, and would have been better off not doing it!

The self-etching stuff never made it through the alclad (we opted to not strip it off), and there are a few places where we've worked and the primer has chipped off. It got NO penetration into the metal and was a waste of time.

Given my location and the enviromental issues I have. Throw the former military, anal retentive, perfectionist, my wife knows so well into the mix and prime it is.

Yes now it's off to the "which one" battle.

Thank you for all the input.

Primer for rust prevention?

There are very few primers that prevent moisure penetration. They are intended to provide a surface that paint can adhere to, and not primarily as a deterent to moisture. I don't recall the two that are moisture barriers right now, but if you do some searches you will see that primers used to prevent rust by keeping moisture out are not effective. Ony a very few are.

I guess the thing that always pulls me toward priming the interior components of my a/c. Is that in all my years flying to put food on the table, seeing many, many types opened up for various inspections. From small cessnas we have owned through numerous corporate jets and while at the airlines the "big iron". I don't ever recall seeing one not primed.

I know slightly different application. However, in that market weight is money and if they do it...

I do have to say, all the support available for a RV builder makes this task seem a lot less daunting.

Thank you all.

JohnF said:

There are very few primers that prevent moisure penetration. They are intended to provide a surface that paint can adhere to, and not primarily as a deterent to moisture. I don't recall the two that are moisture barriers right now, but if you do some searches you will see that primers used to prevent rust by keeping moisture out are not effective. Ony a very few are.

Click to expand...

As far as I know epoxy primer is the only primer that is a moisture barrier. As stated, all the others are merely for promoting adhesion to a topcoat and make no claims to inhibit moisture. This includes the self-etching industrial primers.