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Epoxy Primer Brands (and mil-spec)

zsadecki

Active Member
It seems to me that if you're going to bother priming the interior structure, you're best off using epoxy primer. And if you're going to use epoxy primer, it might as well be the mil-spec (20%+ strontium chromate). This is a reasonable conclusion, right?

So, what different brands of epoxy primer are available? Anybody have any good or bad experiences with specific companies/primers/distributors? What about prices (~$100 to make 2 gallons mixed looks about average)?
 
I'm not a chemist so I can't address the importance of strontium chromate being one of the components of a stand-alone primer.

What I can add in a general way, is that the "dangerous" epoxy primers all have a goodly percentage of strontium chromate while the "safe" ones do not.

For example, the PPG DP40 epoxy primer contains around 10% or so strontium chromate while it's safer PPG alternative (DPLF) has no strontium chromate in it at all.
However, either of those two epoxy primers are suitable for any application where an epoxy primer is decided upon.

If you really must split hairs, and want a bullet proof finish coating from the standpoint of corrosion protection, then how about a coat of self etch primer (e.g. PPG 1791/1792) followed with a slightly overthinned coat of either of the PPG epoxies (DP or DPLF) and go fly?

Considering that you're starting with an alclad finish in the first place, I'm thinking that you might be losing way too much sleep over this. ;)


RV7-A
 
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Thanks for all the replys, Vern.. I'm not losing much sleep over this, just trying to make the best choice I can before I start building. I'm still waiting on tools, so I get to overanalyze things like primer ;)

AFAIK, the chromate chemicals are what are really supposed to give good corrosion protection to aluminum and aluminum alloys. But that same chemical is the toxic, carcingogenic stuff... go figure. I think that any epoxy primer will provide a nice environmental barrier, but from what I've read, if it is scuffed or scratched the chromate will keep that area protected even though the physical barrier has been breached.

After changing my mind on things several times already, I think I'm just gonna end up going the conventional route and etch/alodine/epoxy. It seems that most manufacturers mandate using etch primer only if you can't alodine for one reason or another, otherwise it seems to be just an extra step...

Hopefully my tools will arrive soon and I can start spreading all my (over analyzing) questions on other forums, too ;)
 
Primers

Zach,

I'm currently using the Alumprep/Alodine/epoxy primer method on my RV-8. It is probably overkill but it gives me a sense of security (and I like the green color!). When I get to my fuselage, I may change, but for the insides of the emp and wings where I can't inspect well, I am going to continue this way.

For primer I am using a 2-part water reducible primer from Deft that they make for Boeing. It is still a high Strontium Chromate primer but the fact that it reduces and cleans with water makes it easier to deal with and I don't have the additional solvents to add to the problem. So far it is working quite well.

I am doing some testing with Sanchem's product as a replacement for Alodine and may use that on my fuselage.

I think this is an area where there is no right or wrong answer, only the answer that makes you feel comfortable.
 
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