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Permalink Reply by Dan Hill on September 19, 2021 at 9:06am

commonly between mating surfaces before final assembly. Many are using water based  Cortec which can be supplied by Zenith in small quantities. I use Duplo self etching primer in spray cans for several reasons. Do a search here and you will find lots of threads about priming and corrosion protection. Dan.

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Permalink Reply by Bob Pustell on September 19, 2021 at 9:17pm

Unless you live in a very corrosion prone area or are going to operate on floats, most folks on this group seem to agree that full corrosion proofing is not really needed with our birds. The 6061 alloy Zenith uses is inherently corrosion resistant (while the more commonly used alloys for aircraft construction are much more corrosion prone). So, most here suggest applying some type of corrosion proofing (Cortec or a good self etching primer) to the mating surfaces before assembly, but don't bother putting it on the entier interior surface of the internal structure. All you are doing is adding weight and addtional work to treat a surface that is inherently corrosion resistant to begin with. A significant minority of this group suggest not even bothering with protection on the mating surfaces, just rely on the 6061 to resist corrosion and trust/hope for the best. You will need to make your own decision after checking out the positives and negatives of the various options. I have decided to go with Cortec on the mating surfaces only, myself.

If you plan to operate in a salt air environment or on floats - protect it all, inside and out.

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Permalink Reply by Daniel Niendorff on September 20, 2021 at 2:14am

Lots of opinions exist on the topic of what when and where to prime.  If you want to see pretty much all of those opinions, then jump over to the vansairforce.net site and click on “never ending debates” then scroll to the primer section.  The knowledge base is applicable to Zenith aircraft.

Since you asked if there was something newer and better than zinc chromate,  I’ll put my two cents in.  I’m particularly fond of Akzo Nobel epoxy primer.  It is very easy to use…..  shoots very very well.  And it’s extremely tough.  

There is no one answer to your question.  You will need to investigate your options and decide what you are comfortable with.  After reading the “never ending debate” you will be in a good spot to make choices.

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Permalink Reply by François Balaux on September 21, 2021 at 11:52am

Hi Daniel

I don't totally agree when you say that "The knowledge base is applicable to Zenith aircraft."

Vans aircrafts are made of 2024 which does not have good corrosion resistance. Zenith aircrafts are made of 6061. 

I do not live near salt water and my non-corrosion protected, 12 years old 701 still looks new.

Regards,

Francois

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Permalink Reply by Daniel Niendorff on September 22, 2021 at 5:13am

Hi Francois,

Glad to hear that your aircraft looks good 12 years into its flying life.  Many folks make the same decision you made - not to prime at all.  Others review the data and their own circumstances and make a completely opposite decision - to prime everything.  It is a very individualized decision, based on many things such as your location, your shop/painting setup, the alloys involved, anticipated useful life of the airframe, later resale, etc.....  Of great importance to many is the expected life of the airframe.  Everything corrodes at some rate - how long do you plan to use it?  Some also are concerned that corrosion may develop where it cannot be easily found at inspection, and could present a risk later - so risk tolerance is part of the decision as well. 

My point was only to offer a resource where the topic is thoroughly discussed, and all of these points are considered.  It sounded like to OP was looking for such a resource.

Just to clarify though - Vans aircraft are not all one alloy.  They do contain 6061 parts.  Thoughts on priming 6061 is part of the discussion.  And while it is true that bare 2024 has poor corrosion resistance, 2024 ALLCLAD (which is what the Vans skins are) is more corrosion resistant than 6061.  So the discussion of whether to prime skins is still very pertinent to Zenith builders.

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Permalink Reply by John Austin on September 22, 2021 at 9:05am

Lots of good advice given!  My location in East Tennessee is not a particularly highly corrosive environment, so I did Cortec on mating surfaces.  The exterior was painted with epoxy primer and epoxy top-coat - still looks new almost 10 years later!  I had a pro paint my aircraft, but did learn a bit about epoxy or "2K" catalyzed paint.  It is very toxic during application but almost indestructible afterwards - gasoline, etc, doesn't faze it at all.

At the time of my build back then, I found that Rustoleum made a true, 2K epoxy primer in a rattle can and used that on my engine mount, cabin frame, etc.  It's pricey stuff - I think it was about $25-$30 per can.  You activated it by depressing a button on the bottom of the can to mix the 2 components inside the can and as I recall, had about a 24+ hour pot life.  However, the price was worth it as there was no complicated measuring/mixing and no spray gun to clean afterwards.  To make the most economical use of the expensive rattle can, I prepped more parts than I thought I could possibly paint and kept priming until the can was nearly exhausted.

I now see that Eastwood has a whole line of 2K rattle can paints including primer and color coats.  The prices appear to be similar to what I paid.  I have no experience with them, but I suspect they would be ideal for primering and even top-coating corrosion critical areas.  Way back when I got the Rustoleum, I "think" it was really intended for more industrial-type applications but obviously the Eastwood product is intended for automotive use and likely provides a good finish.  If someone has experience with the Eastwood 2K products, I'd like to hear about it!

BTW, Presta makes a product called "Scuff Stuff."  It looks like a rubbing compound and you can prep a bare metal surface with it using a gray scuffing pad.  It gets in around rivet heads and scuffs - if you use a pad alone, many times you'll get a "halo" of unscuffed metal around the perimeter of the rivet head.  It washes away easily with water and doesn't stick in the rivet head hole where the mandrel breaks off.  Great for scuffing and prepping exterior surfaces prior to primer application.

John

N750A

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