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prkaye

Well Known Member
From what I've read on other posts, this is a controversial topic... so please forgive me. But... an issue I must decide is whether to prime the insides of all my bits as I build the plane. I live in Ottawa, which is very dry in the winter, but can be somewhat hot and humid in the summer. Not near any ocean, so that may reduce corrosion risk.

1) If I decide to prime, this will add to weight and construction time... but how much? how much weight, and how much extra time?

2) If I decide not to prime (and just cover up scratches and rivets with what they call an "Alodine pen" (whatever that is)), will my airplane rust away in 10 yeras, 20 years, or will the airframe still be in good shape in 50 years?

3) If I do decide to prime, what is the typically suggested product and method of application? Can I use the same 20Gal compressor I use for rivetting? What sort of paint spraying attachment thing do I need (HVLP?) ?
 
I Primed

Here's what I did and MY reason(s):

So far the empennage is complete and I'm working on wings. I have primed, and plan to continue priming all internal surfaces with Akzo 2-part epoxy primer. That is TOUGH stuff!!!!

Why? I'm young, don't know for sure were I'll live, or where my plane might want to live after me, if anywhere. I view it as an insurance policy, planning for the worst, hoping for the best. If I move to a seaside environment, I'm ready. If I don't...so what. If for any reason I am no longer able to fly, or decide to change planes and the prodpective buyer finds it important, I'm ready.

How much time does it take? I do all the work I can until I can't do anything else without riveting something together. Then I alumiprep, alodine, and prime everything internal. (The external is still Alclad.) If I remember, the alumiprep and alodine weren't expensive (if you can pick it up, DON'T ship it!! $$$$$$$ Hazmat fees!!! The primer was about $130 for a gallon kit, but will also incur HazMat fees if shipped. I will likely need another gallon kit of primer before all is said and done. (1 gallon primer, one gallon catalyst.) For the Emp kit, the prep and prime took 2.5 days, 1.5 days alumiprep and alodine, 2 half-days priming. I use a cheap-o touch-up paint gun from Home Depot. I think it cost $20. This thing is going to take several years and several thousand dollars for me to build. That's noise both in time and expense.

Ultimately, it's YOUR plane and YOU are building it for YOUR purposes. Build YOUR plane. Learn what you can about the options, weigh the pros and cons based on what's important to you, **** the torpedos, and fire up the compressor.

Hope this helps
 
Insurance

I look at it this way: if 10 years+ from now I get corrosion even though I've primered, then well it was going to happen (and probably will here in the Waikato). If, however, I hadn't alodined and primed as I have and got corrosion, then I'd be wondering (while I'm trying to fix it) whether priming would have prevented it. Sure extra effort, extra expense, a little extra weight; no problem. Rather have the 'feel good' about having done it. Resale probably easier too, if I ever get that far.

Cheers,
 
Here's the part I don't get about folks who prime every part? Why EVERY part?

Take the baggage compartment covers, for example. Why prime a part that's not showing when (a) it's unlikely they'll corrode and (b) it'll add extra weight and (c) if they do corrode to the point where it's a serious concern, you can just buy the part, stick some nutplates on it, and slap it in there?

I get the whole "I live near the ocean" thing but some parts are so small, easily built, easily replaced, easily accessed, and not structural that I don't see what the problem is that requires taking on so much time and weight.
 
I'd be interested in finding out if there is anyone out there who did not prime things kike the insides of the wings, and then later had a corrosion problem and wish they had primed?

I'd rather not prime just for the "feel good" aspect of it... but only if there is good real-world evidence that it should be done.
 
Welcome to the greatest addiction on earth - airplane building! If you think that the priming decision is tough, wait till you ask about tailwheels and nosewheels....

Seriously though, do a search on "Primers" and Priming" on the board, and you will find a tremendous wealth of information already here. Don't expect to find "THE" answer...because there are many different shades of opinion.....Fortunately, I have yet to hear of an RV that was scrapped or crashed due to corrosion, so whatever folks are doing probably works....

Paul
 
prkaye said:
1) If I decide to prime, this will add to weight and construction time... but how much? how much weight, and how much extra time?
Click to expand...
Relatively speaking...
2-part epoxy over alodine = lots more time
Self-etching rattle can primer = a little more time

prkaye said:
3) If I do decide to prime, what is the typically suggested product and method of application? Can I use the same 20Gal compressor I use for rivetting? What sort of paint spraying attachment thing do I need (HVLP?) ?
Click to expand...
Assuming you are spraying primer with a gun... you typically start and stop the gun frequently because you are only priming small pieces, and usually you aren't so concerned about runs or other quality issues you might care about if you were spraying paint. Therefore, you can get away with a smaller compressor that you could if you wanted to spray finish coats (paint). Your compressor should be fine for priming, and yes HVLP is the way to go. I picked up a Sharpe Finex HVLP spray gun new on eBay for $60. It is a great gun and replacement parts (seals/o-rings) are readily available.

FWIW, I am currently spraying PPG 2-part epoxy with a gun, but if I were to do it again, I would just buy a case of self-etching rattle can primer such as SEM (or others).
 
I started out acid etching, alodining, and spraying with PPG self-etching primer. I started with a regular spray gun and switched to a HVLP gun. If you are going to spray, I definitely recommend going the HVLP route. Much less overspray. I bought mine from Harbor Freight for about $50 and it works great.

Now, I just clean the parts and use rattle cans of self etching primer. I have used PPG and SEM. Both work fine. I just bought 12 cans from NAPA when they were on sale. Many on this site have said they like the NAPA rattle cans. On sale they were less than $4 a can. The good part about rattle cans is there is virtually no setup or teardown time. This makes it feasible to prime small batches of parts.

Also, now I mainly only prime mating surfaces.

As has been said, this is one of things everyone ends up having to decide for themselves. If you ask 5 builders their opinions you will get 8 different answers. :)
 
I am priming, but if I started over, I probably wouldn't or would go with a self etching primer. There was an article in a recent RVator that discussed a test they did leaving 3 pieces out in the weather for 2 years. If my memory is correct, here's what they did. One piece was unprimed, one was primed and the third, I believe just had a self etching primer, which provides minimal protection and is what Van's puts on the QB's. Only the untreated piece had significant corrosion.

Also consider: Your plane will most likely be hangared.
Waitin for the right weather to prime could slow your building progress.

I got my zinc chromate primer (good stuff!) for almost nothing, which is the main reason I am priming. It will probably add a little to the resale value.
 
A couple quick notes regarding Akzo. This stuff is tough as heck and dries REALLY quick. By quick, I mean that if you live in a reasonably warm place you can prime and assemble in the same day. Probably within about an hour of spraying actually! Secondly, I think this business about primer adding weight is a bit overblown. The Akzo goes on very thin (.0005, IIRC) so I can't imagine it piling on too much weight. Things like PPG DP primer goes on a lot thicker, as do sanding primers, but this stuff is quite thin. One of these days I'm gonna get a gram scale and weigh a before/after piece to settle this once and for all, but in the meantime I'm gonna continue to believe that the weight penalty is ounces. Come to think of it, I bet you could probably just do a back of the envelope calculation using the weight of a gallon of paint, the transfer efficiency of the gun, and the amount of solvent that evaporates off while drying to get a good estimate. JMHO.
 
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