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To prime, or not to prime.

KellyA

Member
Okay, I know this is probably an ongoing debate but! I’ve just started my build on a RV8, I’m doing the horizontal rear spar and I’m wondering, do I need to prime everything? I live in Canada, not humid during summer, at least 1000 miles from any saltwater, airplane will be hangared. I have a 1966 Cessna 150 and it isn’t primed. So.....?

Kelly A.
 
1. Browse the opinions on VAF using the search function.
2. Flip a coin for your decision and move on.

You'd save a tremendous amount of time and finish the plane sooner by starting at step 2.

FWIW, I chose to prime and would do it again.
 
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Okay, I know this is probably an ongoing debate but! I’ve just started my build on a RV8, I’m doing the horizontal rear spar and I’m wondering, do I need to prime everything? I live in Canada, not humid during summer, at least 1000 miles from any saltwater, airplane will be hangared. I have a 1966 Cessna 150 and it isn’t primed. So.....?

Kelly A.

My understanding of the Canadian regs is the priming is a requirement. I was told this by several builders but never found the documentation on this. I did not look too hard as I had already chosen to prime.
I believe in your case the decision maybe more than just the pros and cons of priming. I would check with your local MRDA.
 
My tail feathers are primed mating surfaces only. They passed the MDRA inspection. Alclad provides corrosion protection for anyone asking. Certainly prime the non-alclad parts.
 
You can chose not to prime and sign the document with the MDRA inspector. That has been my experience. There are no real standards for priming and done incorrectly can cause more future problems then they solve.
An example would be a rattle can primer that is not resistant to 100LL. spilled fuel will get into the wings.
I have primed many of my planes and done others without. Kept in a dry hangar there is no reason that these aircraft will not be around as long as some of the unprimed Cessna 150s
If you live along the coast then you should probably prime with what the professional paint shops use.
 
LP3

I am sure it has been mentioned somewhere in the annals of VAF primer wars.
On my first build RV-8, I sprayed the inside of the wing with LP3. Its great for places that don't get touched. It dries like bees wax and stays "forever".
Excellent corrosion protection. You can apply it when everything is put together before nailing down the bottom skin, same for the empenage parts.
 
As others have said, this Q has been discussed ad-nauseum on the site. But I don't think I've ever offered my .02 so I will do so now :D

I live in the pacific north-wet so it made sense for me to prime and after much research and deliberation I did all my interior parts with expensive epoxy primer they use on Boeing airliners. The stuff is bullet-proof and gives me peace of mind since my plane is hangared 1/4 miles from the pacific ocean. 20 years plus and it's good as new.

HOWEVER if I were to do it again I'd be much less inclined to overthink / overdo - I would still prime but not worry so much about what it is, just get something on there, maybe even rattle-can stuff. People talk about the alclad being adequate by itself, but that thin layer gets scratched and scuffed pretty easily, and I've worked plenty on old Cessnas that have corrosion issues so I feel better with the primer.

One caution - hold off priming exterior surfaces or anything you might be some day putting a finish coat on. Because, a) the topcoat needs to be compatible with the primer, and b) finish paint should go over freshly primed not old.
 
Not wanting to get into a priming debate. I really don't know the answer to this.

Why does Van's prime the QB's and how did they get into recent corrosion issues if priming is not necessary.

Perhaps the voyage from the Philippines?

I also got some surface corrosion on the leading edge of my wing where it sat in a carpeted sling stand for only a couple of months.
 
Nine out of ten MDRA inspectors are probably going to insist on priming. I believe they are most concerned that there is a good primer later between mating surfaces to protect against any trapped moisture. Our EAA chapter Zenith 750 currently under construction has this and it has passed it all of its inspections (only final inspection to go before flight). I personally use a rattle can of self etching primer on my mating aluminum surfaces by first scuffing them up well with red scotchbrite, then a good degreasing/cleaning with naptha (Coleman stove fluid). Really easy to do, quick, and gives me piece of mind.

YMMV, batteries not included, objects in mirror are closer than they appear, etc...
 
Don’t shortcut to save a little time and effort

I used S&W wash primer as recommended by Vans a while back and it became second nature. It’s lightweight, easy to apply, transparent, drys fast and gives outstanding protection of bare aluminum hopefully for the life of the aircraft. :)
 
Prime or not!

Okay thank you everyone for your inputs. I'm going to wait, and talk to my MDRA inspector before I go any further. I've just started my build and working on the front spar of the horizontal stabilizer, no rivets yet. Once again thank you.

Kelly
 
Okay thank you everyone for your inputs. I'm going to wait, and talk to my MDRA inspector before I go any further. I've just started my build and working on the front spar of the horizontal stabilizer, no rivets yet. Once again thank you.

Kelly

Can you let us know what he says?
 
Remember: Your MD-RA inspector can have any opinion they want to on whether or not you need to prime. He can't force you, nor can he refuse to sign off your aircraft, when it's not required by the regulations. MD-RA does NOT write the law.
 
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