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Corrosion Protection Options for Wing Spars

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jonfilipa

Well-Known Member
Supporting Member
Joined
Jun 7, 2009
Messages
51
So I’ve got almost of the components for the wing spars built and am trying to figure out (1) whether it’s worth it to apply some level of corrosion protection and (2) if I do what corrosion protection makes the most sense.

For background, I live in southwestern Ohio and am planning on hangering my Sonerai when it’s done. So nowhere near salt water and (hopefully) not stored outside .

Options I see are:
(1) Two step Alodine + zinc chromate primer. Old school. Given my location this perhaps seems a bit excessive and I’m wary of environmental aspects of the zinc chromate. Particularly since I’m working in my home garage and I’ve got 4 young kids.
(2) Mar-Hyde single stage self etching primer. I like the single stage but $30-$40 for an aerosol can I could see getting somewhat expensive.
(3) Rust-Oleum self etching primer (or similar automotive style primer). Also single application but at $6 per aerosol can quite a bit cheaper than the Mar Hyde.
(4) Do nothing and start riveting.

I’m leaning towards option 3 (Rust-Oleum self etching primer) as I’m thinking it strikes a good balance of appropriate corrosion protection given operating environment vs time/cost/minimizing nasty stuff around the house. All that said, I’m open to any learnings and/or better ideas others have. Any and all feedback is appreciated!

Jon
 
I would recommend something. I did option no. 1 to the spars and ribs but nothing to the skins. Not sure if that was smart but that's what I did. I'm in Pennsylvania with a climate similar to yours. The worst time for corrosion is winter, when (relatively) warm moist air moves in after everything has been soaking in colder air. I went to the hangar on a foggy day in January several years ago and the poor thing was literally dripping water. Nothing I could do at that point but wait for the weather to change. I have no experience with (2) and (3). Maybe they are perfectly good.

Ed
 
I've had better results with the Duplicolor self etching primer than with Rust-Oleum. More uniform coverage and less clogging of the nozzle. But I used the two step Alodine + zinc chromate on my spars and ribs.
 
I used ACF-50 took about 1/2 gal for a 172 so a quart would most likely do fine I did it 3 years ago and is still there. is a hangered plane. I sold that plane 2 years ago to a friend I still have a set of keys and can use it any time I want. As I have mentioned before I have an L-17 Navion which was comate primed at the factory I also have found the nozzle on the dupa color is better and the preKote Idea sounds like the best
 
I concur with thought process to do some level of corrosion protection. At least for the spars. PreKote seems like a good surface pretreatment option per my quick review of what I could find on the manuf's website and/or on Aircraft Spruce.

Regarding picking a primer for internal aluminimum parts, I'm leaning towards spraying on a light coat of zinc phosphate. Less toxic than zinc chromate but supposedly still pretty good relative to corrosion protection. Also like the idea of minimizing thickness buildup for riveting and making sure spars assemble into the spar box. For me zinc chromate seems like the best option for internal wing spar components and epoxy seems like the best option for the basic airframe (compliant with fabric manuf of course). If others have experience refuting this feel free to let me know :)

Have read some good reviews on Corrosion X but my initial thought is this is more something to apply to external surfaces on an annual or semi-annual basis and not necessarily for internal areas you either don't have access to or don't want to have worry about in the future. As anyone may have guessed this is my first rodeo in trying to corrosion proof airplane parts so if I've got something wrong here let me know.
 
corrosion X has a nasty smell to it and it seems to stay for a while. ACF-50 actually smells nice the reason I used on my Cessna can be used on all internal aluminum surfaces. not sure how it is with fabric. I had to wait over a year before I could paint the plane after spraying it. It was still weeping thru the cracks and rivet seams, for at least 9 months.
 
Thanks for everyone's feedback. Really appreciate it. So I think I've settling on Prekote + 2 part epoxy primer. Regarding picking a 2 part epoxy primer, I see the following options:
- Akzo - green only
- Epibond (Randolph) - green or white
- Stits - green or white
- Superflite - white

My thought process is:
- I'd like to use the same primer for both the internal wing components as well as the fuselage. Simplifies things and avoids having to learn a new system. Although I'm guessing they all go on the ~same.
- I'd rather have a white fuselage than a green one, which means the Randolph, Stits, or Superflite primer.

Curious to know if anyone has a strong preference between any of the epoxies. And if the Akzo primer is for any reason significantly easier to apply or offers better performance I can get over my color preference.

Follow-on questions:
1) Anyone have a favorite HVLP spray gun at a reasonable price?
2) I'm estimating that the directive for putting primer on the internal wing spar components is to keep it reasonably thin to avoid any issues when riveting it all together. If I'm off base please someone let me know.

Jon
 
Your exterior primer should be whatever is recommended for the paint system you plan to use. Not uncommon to use green or yellow primer inside the wing and then the white primer recommended for the exterior paint system. Also, I believe Stits and Randolph both recommend finish paint within so many hours of priming. If you want the least amount of paint weight added to the aircraft, it'd make since to hold off on priming the exterior till you're ready to paint.

For, HVLP IF you're gonna go with polyurethane finish, you might want to consider one of the Paint/airline respirator dual turbine set ups. If you're using the "low-voc" paints, then there are plenty of choices out there, ranging from inexpensive ones from the hardware store to the super pro models from Eastwood. The only catch is if you go with a traditional compressor charged HVLP, you've gotta make sure your compressor can provide clean and dry air at the CFM rating required by the gun.

On my RV-8, I'm priming internal surfaces with SEM rattle can "self-etching" primer (the wing spar is anodized). I match-drill, de-burr, scuff and clean for a break-free finish. Then I spray, either outside (>70f) or under lamps, 2 to 3 wet coats. Then, let cure for 24hrs before riveting. All dimpling and countersinking done before priming. Everything goes together no problem.
 
On HVLP guns, especially for priming, you can just use a cheapo from Harbor freight. They work really well and are about $15. I painted my Sonerai with one and also painted this truck hood with one too. Both finishes are urethane as sprayed from the gun with no buffing. The truck hood was a base/clear, and the Sonerai was a single stage. Note the Sonerai wheel pants aren't painted and still in 29 year old gel coat. All of these paint coats were done with the same gun from primer to top finish. This is the one I have. Actually have 3 of them. https://www.harborfreight.com/20-oz-hvlp-gravity-feed-air-spray-gun-62300.html

IMG_20170704_075038.jpg

20200816_162718.jpg
 
BTW, I tried the rattle can epoxy primer that is 2-part and you push the button to mix and then shake. Worked fine, but I really wasn't that impressed. There didn't seem to be a lot of paint in the cans, and the nozzle was worse than some hardware store rattle cans. For small touch up they would be fine but if I were going to prime wing spars or skins, they are big enough that I'd just mix up some from cans and run it through the HVLP gun. My 2 cents.
 
Always good to hear the cheap option is a good option :) . And nice work on the paint job for both your truck and your Sonerai.

So question on quantity of primer to purchase. I see a 1 quart option and a 1 gallon option. Is it reasonable to assume that the 1 quart kit will be enough to do the wing spar channel/spar cap strips/angles/etc or should I just bite the bullet and buy a 1 gallon kit?

Jon
 
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