Hey everyone

Does anyone know where I can buy the brush on water based primer Zenair/Zenith uses

I called the factory and they said aircraft spruce sells it, call aircraft spruce and they dont know what I`m talking about

this is the link to the primer page...can anyone point me in the right direction?


Thank you

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Did you talk to Zenith in the USA?  The primer is called Cortec and normally they (Zenith) sell it by the quart, which is plenty for the whole build.



I found the manufacture and product page, I`m going to call them next week and see who sells it in Canada

I did already call zenair canada to inquire about buying from them but they dont seem to sell it. chemicals like these might be more trouble then its worth to sell, hazardous charges on shipping, things like that.


VpCI-373 is a water-based wash primer used for bonding
other primers and coatings such as
VpCI-386, to a variety
of metal substrates.
VpCI-373 is applied at an extremely
thin thickness of 0.5-1.0 mil (12.5-25 microns) DFT. When
used in conjunction with topcoats, this product can extend
protection significantly.

I think you'll readily find vendors for Cortec in Canada, but you'll probably find it is only available in 5 gallon containers (the next available size is 55 gallons!) and will be extremely expensive since you'll only need a quart at best. I did a quick Google and couldn't find a price for 373, but there are many other similar Cortec coatings and they run about $250-$350/5 gallons USD.  My understanding is that Zenith in the US buys it in industrial quantities and then repackages it in 1 quart containers (more than enough for a build).  You'll likely find it much more economical to buy the quart from Zenith and pay shipping vs purchasing 5 gallons.

Of course, if you've got 19 other builders who want to go in with you on a 5 gallon purchase, then ...   ;>)


I use Martin Senior Zinchrome primer 7222 in spray cans from NAPA it is a self etch product and works very well , 

Cortec is merely raw latex rubber.  You should thin with ammonia to keep it from solidifying.  If you add vinegar you will get a lump of polymerized rubber!  Great product which by the way can be removed after it dries with either acetone or lacquer thinner.  I used the product on all mated surfaces during my Cruzer build.  One can is plenty as John Austin says.  So go to the internet and see which craft stores sell raw latex.

John Minatelli

How did you arrive at the conclusion "Cortec is merely raw latex rubber" ?

Simple:  I have a PhD in organic chemistry and worked for Uniroyal for 11 years where I handled raw latex all the time.  They owned huge tracks of rubber tree plantations in Indonesia at the time and the polymerized form is still the major polymer in many tire formulations.   We kept the raw form (Cortec) in the liquid state by making sure the solution was basic (aka high pH) by adding ammonia.  When I first opened my Cortec from Zenith there was an instant flashback to the good old days at Uniroyal.


PS you can buy it at Hobby Lobby.  Ever wonder why that latex based paint you buy to put on your house walls smells like ammonia?  Now you know, it contains raw latex!  You can search the term “liquid latex” to see how easy this is to obtain.


John, how much ammonia per qt? And, if one does not add ammonia, what's the best/worst that will happen?

If the Cortec is getting on the stiff side just add 2 tablespoons of soap free household ammonia, however if it is free flowing as received and has the ammonia smell when opened you probably need to add no ammonia at all, only add it if the Cortec is thinking up Jason.  If you don’t add ammonia to keep it free flowing overtime it will simply get thicker and thicker until it is too stiff to easily thin out with a brush on each mating surface.  


Gotcha, thank you very much. My rudder skeleton is ready to rivet, so have been looking up more info on the qt of Cortec I have sitting here.

Caleb, the engineer at Zenith (years ago) said to simply thin the Cortec with water until you get a consistency that leaves a thin film and brushes easily.  I used disposable foam brushes. I would put a dollop (sorry for the technical terms! LOL!) in a plastic lab sample cup, thin it with some water, and recapped the cup when I was finished to save the thinned Cortec for next time.  As long as you put down a thin film (which is all you need), it'll dry relatively quickly thinned with water.  I've seen some recommend thinning with alcohol, but can't speak to whether that's a good idea or not.  I never found the drying time with water as a thinner objectionable. 

John M's comments about adding ammonia was interesting - so interesting, in fact, that I went out to the garage and got my can of Cortec that I used during my build years ago - the Cortec was at least 10 years old.  It "looked" OK but was gummy but not solid, so I added small amounts of ammonia and started stirring and sure enough, it regained a liquid consistency and I suspect would be perfectly good to use ... is that excuse enough to start another build? Ha!




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