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Chromate Free Epoxy Primers - Any Experience?

StressedOut

Well Known Member
I'm currently using Akzo Nobel 2-part epoxy interior primer on my RV-14A build. I've had a few priming sessions, but I'm still not entirely comfortable with using a chromate based primer. There are some water-based single component primers, but I understand they aren't as durable as epoxy primers and can be wiped off the certain solvents.

I recently discovered a chromate-free epoxy primer made by PPG Aerospace. It seems to be just what I'm looking for, but it's pricey ($327/gal on SkyGeek) compared to $189/gal for the Akzo Nobel stuff.

Has anybody had any experience with this primer? I'm mostly interested in its durability compared to the chromate-based stuff. I'm willing to pay the extra money if the associated cancer risk can be significantly reduced or eliminated.
 
I have not used that PPG primer but I have used Stewart Systems EkoPoxy which is water based, non-toxic, and carcinogen free. It has worked well for me so far. I have found that EkoPoxy starts to get really durable after curing for about 48 hours, but before that time has elapsed I can scrape it off with a finger nail. I haven't used any other epoxy primers so I can't comment on how durable it is compared to others.

Once or twice now I have decided that I sprayed the primer on some parts much thicker than I intended and wanted to remove it and give it another try. After the parts had dried over night I was able to remove the primer with a rag and lacquer thinner but it took a lot of elbow grease and a good chunk of time to remove. So even though I was able to remove it, I wouldn't worry about it coming off easily.

My biggest complaint about EkoPoxy is that it doesn't seem to lay down as smooth as I would like. However, this is probably entirely my fault because I didn't have any experience with a spray gun before I started to use this stuff, and I'm probably not spraying it on quite the way it was intended since I'm trying to keep it thin and light. Also, with my last batch of priming I managed to do a pretty good job of spraying it on in a thinner layer than I usually do on some parts. The primer on those parts seems to be a little less durable though than other parts where it went on a little thicker. So it may be that this primer needs to go on a little thick to be as durable as it can be. It could also be that I've reached the end of the shelf life for the gallon I ordered. I think it's supposed to be good for a year and I've had it for a year and a few months.
 
I use this stuff:

http://us.ppgrefinish.com/PPG-Refinish/Products/Automotive-Refinish/Shop-Line

Pick your primer to fit your needs or desires - top coat (using their epoxy primers) can be anything you want.

The Shop-Line setup sure sprays good for me! I an using Klass Kote for the top coat. http://www.klasskote.com/

I used the Stewart products on the B25 I used to fly - it sure worked on the fabric surfaces!

I think we primed with PPG epoxy, as that is what I had here. I used a 4-2-1 mix to get the thin coat it sounds like you want. (4 primer/2 activator/1 thinner).
 
Hi Art,

I had the same opinion as you regarding the chromates. Why build an aircraft that will last 100 years if you don't because you've been sucking on chromates the entire time. I used Stewart Systems Ekopoxy for the majority of the build, and a good quality zinc phosphate etch singlepack for the remainder of the components. The Ekopoxy seems quite durable, however I can not talk to the long term corrosion resistance of it. The zinc phosphate self etch (Wattyl aka Valspar superetch) is not quite as durable, but is easily touched up as it comes in a rattle can (or I use cotton buds dipped in it) and again, in theory (at least according to the Valspar datasheets) it is corrosion resistive, but I can't speak to it's long term performance. Both can be removed with acetone, however neither can be removed with Automotive Wax and Grease Remover, so this is what I use before I stick down adhesive standoffs etc. I was looking at a Cessna that was going through corrosion inspection the other day, and noted that the areas of corrosion always appeared between the faying surfaces, and not just on a random surface. Thus I am even more convinced that if you don't want to screw around with corrosion, the key to a corrosion resistant aircraft is sealing moisture out of these faying surfaces. I used a polyurethane sealant to fay seal my fuselage belly (in addition to priming using Ekopoxy). Polyurethane sealants however still contain isocyanates and a lot of other nasty solvents, so even these aren't good for you. I think the key is using a modified silicone sealant, as these are generally solvent free, contain no isocyanates and are neutral curing (non corrosive to aluminium). The only issue is finding one with a long enough working time. The working time on the Sikaflex Pro I used was amazing (hours) and sometimes this is what is necessary when joining major assemblies. I prefer to rivet when still wet, rather than waiting for things to cure with the clecoes in, as it leaves the minimum possible amount of sealant in the joint. They added weight of the sealant was negligible (a few grams) as most of it oozes out and can be cleaned off. Thus, when I build the next one, I'll be doing some hunting for some long working time Modified Silicone Sealant and will be using etch primer on just the 6061T6 components.
Tom.
 
I recently discovered a chromate-free epoxy primer made by PPG Aerospace. It seems to be just what I'm looking for, but it's pricey ($327/gal on SkyGeek) compared to $189/gal for the Akzo Nobel stuff.

I think the key feature is resistance to liquids we don't use, like Skydrol.

I'd suggest ordinary PPG DPLF epoxy primer, two cross coats. Lead and chromate free.

DBC basecoat under DCU2021 clear has been very tough.

http://us.ppgrefinish.com/getdoc/f46758f5-5282-402d-9541-9c917e6fe8bb/Deltron.aspx
 
Compatibility

Nothing to add about primers but I would recommend thinking forward and talking to tech support for whatever final interior paint you plan to shoot. Nothing worse than finding out after that first coat, the two paints are incompatible and it has to be sanded down to bare metal. Nope, not me.
 
I don't know first hand about that primer, but Azko Noble epoxy primer has a well-earned reputation for being tough, durable, strong and effective.

Dave
 
Epoxy Primers

I've sprayed several different epoxy primers over the years. PPG and DuPont (now Axalta) included. Most recently a friend recommend I try the epoxy primers sold by Summit Racing. Very reasonably priced and they seem to work great! They can be thinned for better spraying with Laquer thinner. You might want to give it a try....comes in a few different colors.

Ellis
 
Read these:

http://www.vansairforce.com/community/showpost.php?p=1007375&postcount=1

google this and read: AFRL-RX-WP-TP-2008-4012

Conclusion: primer only - use strontium chromate , Full system with top coat: use non-chromate, magnesium rich with all the specified components of the paint system, just dont mix brands. (per testing and reports)

Nearly any primer works for non-2024 alloys, so use what sticks, but for 2024, be careful if you want serious proven protection.

Except for marine zones (under 3000' and/or within 20/30 miles of the coast), any good primer (and good surface prep) that sticks should work.
 
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