Zenith Aircraft Builders and Flyers
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Corrosion protection
Just wondering what product builders are using for corrosion protection between mating surfaces during the build process?
Replies to This Discussion
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Permalink Reply by John Austin on
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Zenith recommends and sells Cortec primer. It's relatively less toxic than other primers, thins with water, and can be applied with a brush on mating surfaces. I wouldn't use it on an exposed surface that will be painted and where you want a nice finish - it's not a paint primer. Normally, most let the parts dry and then assemble, but you can assemble parts while the Cortec is still wet, but only do this on final assembly where they will not be taken apart again as it will glue parts together as it dries. It's only available in industrial quantities but Zenith repackages it in quarts - a quart will easily do the mating surfaces of your entire airframe. Prep the metal with an acetone wipe-down and a Scotchbrite abrasive pad. I usually put a glob (sorry for the technical terms, LOL!) in a small medical sample cup with a lid and thin it with water to the desired consistency so it will brush and leave a thin, smooth layer - I used disposable foam brushes. The unused portion can be capped and used later.
John
N750A
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Permalink Reply by Kim Dunford on
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Thanks a ton John! I’ll check and see if Zenair has any on hand or have Zenith ship it with my kit scheduled to arrive at Zenair the end of the month.
Best regardsKim
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Permalink Reply by Frank Stutzman on
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I just got my super duty tail kit last Tuesday - the journey starts!
Anyway, I ordered a quart of Cortec along with it. Seems like it was readily on hand.
I treated my rudder spar and doublers yesterday with it. Pretty much used the procedure John suggested except that I wiped down my parts with isopropyl alcohol and also thinned the Cortec 50/50 with the alcohol. I went with the alcohol as its a bit less volatile than acetone (small shop, don't want to get any more loopy than I already am) and should dry faster than water thinning. Got the idea from "sumguy on the internet". Counter opinions?
For what its worth, while brushing it on, it seemed really streaky (if thats a word). Despite working hard on it, I never seemed to get an even coat. Looking at it after it dried, it looks ok. It dries clear, which I'm not really keen on as I can't tell if I missed a spot.
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I "think" alcohol and even ammonia are OK to thin the Cortec, but Caleb, an engineer at Zenith years ago, personally told me to use water. You might try water just to see if it helps with getting an even coat - perhaps a volatile like alcohol dries too quickly and doesn't let the Cortec flatten out? I did find there was a learning curve as to how much to thin it to achieve even coating. Also, a thin coat, even thinned with water, will still dry relatively quickly in warm, dry ambient conditions. But, as previously mentioned, if it is a final assembly of mating surfaces of parts, it's OK to go ahead and rivet them with the Cortec still wet or tacky (again, according to the Zenith engineer).
John
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Well, I did some more parts yesterday. This time I thinned it 50/50 with water. Seemed to go on about the same, but looking at it this morning it looks like it dried a bit more smoother. The alcohol thinned ones seemed to have a bit more runs and bubbles. Not a lot, but I think there is a difference.
Going forward, I'm going to stick with water for the thinning.
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If you've not already tried it, also try a foam brush to apply the Cortec.
John
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Been using the foam brushes from the get-go.
I try to only change one variable at a time - Hey, this is experimental aviation!
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Permalink Reply by Bob Simmons on
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The Cortec sold by Zenith is VpCI-373 (https://www.cortecvci.com/wp-content/uploads/VpCI-373NEW.pdf). Note that the shelf life is one year (mine is therefore no good anymore). Also, don't let it freeze until after it has been used and cured.
Order from Zenith here:
https://www.zenithair.co/zenithstore/product/vci-373-cortec-primer/
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Permalink Reply by Daniel Niendorff on
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I used Cortec When I built my 801. It was completed in 2017, and I have seen no corrosion issues. However, for my next build I have been using Akzo Noble epoxy primer. It is a little more work to use, but I think the ultimate protection is better. It produces an extremely durable result.
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I used Cortec on the mating surfaces and epoxy primer on the exterior - that airframe is going to last a lot longer than I will! LOL!
John
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FWIW, this thread made me curious about the use of Rustoleum Selfl-Etching Primer as a corrosion preventative. Of course, self-etching primers are used to etch the metal substrate to provide a mechanical bond so the paint will stick. However, I believe it says right on the can that it prevents corrosion, too. I use it frequently on metal parts I'm going to top-coat and paint - usually I apply the primer, then a sealer, and then a top-coat.
I've seen it frequently used by others as a corrosion preventative on mating parts and also as a single-coat spray to paint the entire aluminum part such as brackets, ribs, etc. It always bothered me that I didn't think this was really the correct intended use - as previously explained, it's a primarily a paint primer. (Pun intended!)
I contacted Rustoleum to see what they said and the reply was this: "In regards to the Self Etching primer, yes, it is recommended that it be top-coated as it will break down and not last long without it."
I did not specifically ask about mating surfaces, so I don't know if the break-down will occur since these will be relatively protected areas, but looks to me Cortec or epoxy primer are likely better choices.
John
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