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Old 05-18-2018, 01:29 AM
amerkarim amerkarim is offline
Join Date: Nov 2017
Location: Houston Tx
Posts: 28
Default Another priming thread - Advice please

Hi All,

I am now at the planning stages of my RV 10 build and because my airplane is going to spend its life near the ocean, I would like to prime it and protect it as much as possible. I am going to build a large dedicated spay booth for the purpose and have got some large tanks to allow dipping of things in Alodine etc.

My plan was to lightly scuff with a Scotch bright pad, wash with soap and water, then wipe down, dip in Alodine, then once dry, apply a coat of epoxy primer to all the surfaces and parts.

Also to do any dimpling after the primer has full dried.

Regarding the skins, is there any benefit in priming both sides of the skins at one go. I intend to paint the plane once its finished anyway. But it just seems like common sense to me that priming both sides of the skin will be easy in a spray booth and you wont miss any spots, and also protect the outside against corrosion during the build process and build delay. The outside and inside can then receive the final coat of paint once assembled.

Any suggestions, hints, comments or experience would be welcome

Thanks in advance

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Old 05-18-2018, 05:27 AM
rv8ch rv8ch is offline
Join Date: Feb 2005
Location: LSGG
Posts: 2,406
Default dimple then paint

Sounds like a good plan. I'd dimple then paint. I'd also let the painter do the outside. You'll get 999 other opinions on both in the next hour or two.
Mickey Coggins
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Old 05-18-2018, 05:53 AM
fixnflyguy fixnflyguy is offline
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 951
Default A couple things..before the war starts..

First off, The skins are "Alclad", a thin layer of pure aluminum which helps protect from the elements, but the edges are most vulnerable. Think of your skin as a sheet of plywood, and what plywood does when wet. I built my -4 to survive conditions of a seaplane, and fully primed inside skins,and all structure. The outside of the skins where primed at the time I applied paint. I took a slightly different approach to application that works very well and creates no mess on the inside of the skins, using 2 part urethane primer overthinned and applied with a smooth foam roller, after all countersinks and dimples are completed. Any bolt hole or rivet hole in the entire plane has been "swabbed" with a Q-tip dipped in primer to coat the edges. The rolling technique will pretty well cover the dimpled backside holes, and swabbing isn't needed. My internal primer coat is very thin, and added very little weight.It may sound a bit overboard, but 38 years of being an aircraft structural specialist for my day job has shown me the reasons why I did it. Be prepared for the war you may have started!!
Bill E.
8A7 / Advance NC
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Old 05-18-2018, 07:16 AM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 4,635

Originally Posted by rv8ch View Post
Sounds like a good plan. I'd dimple then paint. I'd also let the painter do the outside. You'll get 999 other opinions on both in the next hour or two.
+1 998 to go.

1st Flight 1-27-18
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Old 05-18-2018, 07:18 AM
RV7ForMe RV7ForMe is offline
Join Date: Jul 2015
Location: Europe
Posts: 413
Default I will second that...

Originally Posted by rv8ch View Post
Sounds like a good plan. I'd dimple then paint. I'd also let the painter do the outside. You'll get 999 other opinions on both in the next hour or two.
What he said!

I do deburr, dimple, scuff, clean then prime within a 2 hour window... 2K Epoxy pimer. Be ready for this to double your build time!
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Old 05-18-2018, 08:00 AM
PilotjohnS PilotjohnS is offline
Join Date: Jan 2016
Location: Los Angeles
Posts: 588
Default Priming fuse

I primed everything so far. The real hard part is priming the fuselage. There are so many brackets and stuff on the cabin bulkheads that need to be primed before assembly. And if you wish to paint before assembly, this adds another complexity. I’ll get thru it, but it isnt like the wings or tail where you can rough assemble, prime, final assemble and go. The fuse is where a semi permanent paint booth would be worthwhile.
John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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Old 05-18-2018, 08:23 AM
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agirard7a agirard7a is offline
Join Date: Aug 2009
Location: Newport, RI
Posts: 641
Default My 2 cents

Do you really want primer on the outside of the skin? That will need to be scuffed and re-primed again before painting? Finish paint needs to be applied over an epoxy primer within a short time frame otherwise it needs to be scuffed well before paint is applied.

Also, I’m in favor of priming after dimpling. It’s the edges of the debured, dimpled hole that no longer have the allcad coating. I have done this with SEM primer which is very thin. The one concern is that epoxy primer is thicker and may build up or settle in a dimpled hole. I think if you apply a thin coat of epoxy by tuning down your spray nozzle, it should not be an issue.
Al Girard, Newport, RI

Last edited by agirard7a : 05-18-2018 at 08:26 AM.
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Old 05-18-2018, 08:53 AM
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Carl Froehlich Carl Froehlich is offline
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 1,812

If you use a good two part epoxy primer, skip the alodine all together.

I do slow builds. After competing all part fabrication, fit up and dimpling, then it is time to prime. For prep I use Alumiprep and maroon Scotchbrite pads, then rinse with a lot of water. Prime the same day as prep. I alway prime outside with no paint booth so managing priming days around the weather is a factor.

The hardest part in all this is working sections of the build up to the part where you have to rivet something together. Here you have to stop, put the parts in the “prime bin” and then move onto the next section. At some point you get where you have to prime before moving on. The wings may need two priming sessions. The fusleage (current RV-8 project) needed four. I’m careful to not prime the outside skins or cabin skins that get interior paint other than the overlap areas. They will get done on final paint.

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Old 05-18-2018, 09:04 AM
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wirejock wirejock is offline
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 3,069
Default Alodine

I also prime after dimpling. Specifically debur, scuff, dimple, wash with Bon Ani and gray Scotch brute, rinse, dry, prime.
I Alodined the exterior. If I build another, it will be Alodined inside and out before assembly.
I found Alumiprep easier to use as a pretreatment for Alodine. Both Alumiprep and Alodine should be rinsed. Capturing the rinse is a challenge. I made a slice from a shower curtain. It drained into a huge storage tub. The tub was left to evaporate in my storage building till the liquid was almost gone. Transferred it to a stable plastic container and disposed at a Haz Mat facility. There's a Kitplanes Tip section with link on my blog describing it.
Larry Larson
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Old 05-18-2018, 11:44 AM
rvbuilder2002 rvbuilder2002 is offline
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,945

Originally Posted by amerkarim View Post

Regarding the skins, is there any benefit in priming both sides of the skins at one go.

The catalyzed primers used with with contemporary paint systems require them to be top coated within a very short time (sometimes only a couple days) or they must be sanded and then recoated with primer again just before spraying topcoat.

More work, more cost, more weight, no benefit.

Etching and alodyn in advance on the outer surfaces is fine.

Considering the health dangers and environmental impacts, and the personal experience of how protected alclad aluminum with even just a very basic sprayed on protection (washer primer) holds up in harsh environments, I personally would skip the etch and alodyn.
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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