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Old 02-24-2015, 09:55 PM
N546RV's Avatar
N546RV N546RV is offline
Join Date: Aug 2010
Location: Brookshire, TX
Posts: 1,215
Default Primer report: Stewart Systems EkoPoxy

Background: I'm currently in the final stages of major wing work; basically all I have left are the ailerons and flaps. Up to this point, I've been using rattle can primer; I started with Dupli-Color on the empennage and later switched to Napa 7220 with the wings.

With the fuselage kit on order, I got to thinking about some long-term decisions, most notably what I wanted to do for the interior of the plane. I also figured that at some point I should get comfortable using a spray gun, since it seems like a skill that may be needed once I get around to doing fiberglass work. Finally, I'd been intermittently reading about the products offered by Stewart Systems, and I was intrigued by the not-so-toxic stuff.

So after thinking it over quite a bit, I ordered a gallon of EkoPoxy in Smoke Gray. I considered getting a quart to start with, but I felt fairly confident that this stuff would be good enough that I'd end up using it. Even if I didn't feel it would work as a top coat for the interior, it'd have to be pretty crappy for me to not want to prime with it at all. I also bought a Grizzly LVLP spray gun from Amazon. I went with LVLP after comparing what my compressor was capable of vs. what most HVLP guns wanted.

Finally, last Saturday was D-Day. I tinkered with the gun a bit, first shooting water and then thinned latex paint to get a feel for controlling spray pattern and such, then I decided to cut some scrap into test patches, mix up a batch of primer, and try it out. The results were...acceptable. I got carried away on one test patch and made some nasty runs, but the others I got a fairly even finish, though there's definite orange peel texture. Still, the semigloss finish and color look nice, and I think it'd work great for the interior in terms of aesthetics.

The best of all my test patches:

Tonight, after letting the patches cure for a few days, I did some durability testing. The first test was a brisk rub with an acetone-soaked shop rag. It was immediately clear that primer was being removed; the orange peel texture as well as the gloss vanished from the rubbed areas.

Upper portion of this patch is untouched; center area has been rubbed. Note the difference in gloss:

Ruboff on the shop rag:

Next I went inside for some scratch testing with a thumbtack. The areas rubbed with acetone definitely seemed softer than the untouched parts; the scratch almost immediately showed bare metal, and a little back-and-forth scratching revealed a large area of Al. The area where I hadn't rubbed with acetone was tougher; light scratches were barely visible, and heavier scratches didn't seem to go right down to the metal. I was still able to get down to the metal with some concentrated back-and-forth scratching, though.

Scratch test results. Left side is acetone-rubbed area, right side is untouched. Note how much more metal I was able to reveal in the acetone-rubbed area:

Finally, I went back out to the garage to do some more acetone rubbing. I suspected that with a little more attention, I could remove the primer entirely, and I wasn't wrong:

At this point, I'm wondering if the primer needs some more cure time. I looked a the can again, and I note that it says that after five days, the primer should be sanded before applying a topcoat. This leads me to believe that perhaps the primer isn't totally cured right now. (It's been about three days) Additionally, it's been unseasonably cold here in Houston, and these patches probably haven't been above 45F since Sunday afternoon. As such, I've moved the remaining three patches inside the house, where I'll let them sit for another 2-3 days before I do another series of durability tests. I'm hoping to see increased resistance to solvents and scratching.

Overall, right now I think this is still a decent candidate for an interior topcoat, though I worry about the solvent resistance. I don't plan on rubbing my interior with acetone, but who knows what I might spill or drip in there. Resistance to physical abuse is pretty good, perfectly suitable for interior use, I think.

Bottom line, if I see improved durability after a few more days of curing, I'll be good with this for the interior. If not, then I'll probably think about shooting a separate topcoat. We shall see.
-8 fuselage in progress (remember when I thought the wing kit had a lot of parts? HAHAHAHAHA)
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Old 02-24-2015, 11:05 PM
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JanRV6UK JanRV6UK is offline
Join Date: Jul 2009
Location: England
Posts: 470

Any of the "water based / Water soluble" primers / paint need a long time to cure ... 3 to 5 days .. or even longer ... I have used JetFlexWB in the cockpit ... temperature when spraying was not ideal ... 15 DegC ... then I had to go away for a few weeks ... when back ... could rub with MEK .. no issues ... I have used the Dcup from system from Devilbis and find it so easy to push out the air .. and keep the paint in there for later use .. I used it with my non Devilbis spray gun .. just get the right adaptor.

Slooow RV6, no hole, builder in UK
Paid up for 2015 ...
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Old 02-25-2015, 06:48 AM
YellowJacket RV9 YellowJacket RV9 is offline
Join Date: Oct 2012
Location: Clearwater, FL KCLW
Posts: 1,374

I have primed my interior with the stuff; the cockpit area is painted over as well. I have found that it is MUCH tougher after a week or so.

Chris Johnson
RV-9A - Done(ish) 4/5/16! Flying 4/7/16
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Old 02-25-2015, 09:19 AM
ReidVaitor ReidVaitor is offline
Join Date: Jun 2006
Location: SoCal
Posts: 194
Default Stewarts Systems

I painted my complete plane with the Stewarts system. I found that even with my lack of experience with spray painting that the paint cured slowly (1 week) Since than the paint has held up very well after 4 years.
My suggestions is called Stewarts and ask for Dan. He will spend as long as you want answering any questions and best ways to use their primers and paints.
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Old 02-25-2015, 10:39 PM
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wjb wjb is offline
Join Date: Nov 2012
Location: Half Moon Bay, CA
Posts: 1,168

I've been using the non-epoxy EcoPrime from Stewart Systems for the inside surfaces of the bird. It does take a long time to fully harden (about a week), but when done it's quite tough -- none of the abrasion tests you used would take it off. It's not solvent proof, so acetone or MEK would dissolve it slowly. However, I don't plan to fly through many MEK cloudbursts, so no worries!

The outside of the plane will be done in some fully compatible system; don;t know what yet...
Bill Bencze
N430WB RV-7 @KHAF, Flying 200+ hrs
VAF 2022 donation happily made
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Old 03-03-2015, 10:27 PM
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N546RV N546RV is offline
Join Date: Aug 2010
Location: Brookshire, TX
Posts: 1,215

Update: Tonight I grabbed another test patch for some abuse. At this point, the primer has had about ten days of cure time. Acetone resistance did seem to be improved, though a good brisk rub did still remove some primer.

As before, the dull area can be seen in the center of this patch:

Doing a second acetone rub after some scratching reveals bare metal as before:

However, scratch testing on primed areas that I didn't hit with solvent turned out quite well. Tapping the primer with the point of a thumbtack revealed no visible damage, and light scratching with the thumbtack made marks that were only visible under careful inspection.

It took quite a bit of repeated abuse with the thumbtack to make these scratches:

Overall, I'm quite pleased with the durability and appearance of this stuff, so I'm sticking with my plan to use this as an interior topcoat.
-8 fuselage in progress (remember when I thought the wing kit had a lot of parts? HAHAHAHAHA)
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Old 09-01-2019, 11:29 PM
GPV GPV is offline
Join Date: Apr 2019
Location: QLD, Australia
Posts: 47
Default Mixing Mate

Is anyone successfully using ekopoxy with mixing mate paint lids? I hear it's really thick so was wondering if this would cause issues when mixing and pouring (perhaps too thick to pour).


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Old 09-02-2019, 06:00 AM
Reflex Reflex is offline
Join Date: Jan 2015
Location: Kansas
Posts: 230

I've been using EkoPoxy since the beginning of my build. My belief is/was that EkoPoxy is not as robust as Akzo, however it should have no problem serving it's purpose as Van's doesn't require priming the inside of the aircraft.

I used EkoPoxy for the following reasons:
  • Environmentally/human friendly
  • Ease of cleanup
  • Ease of disposal
  • Uses distilled water for thinning (not reduction)
What I have found is:
  • EkoPoxy is like cookie dough out of the can and remains thick after mixing to the proper ratio. It must be thinned before spraying
  • Sprays like a dream if mixed with additional distilled water.
  • Is NOT acetone proof. Kind of resistant, but will not stand up to acetone long or even medium term. This makes acetone a good cleaner for spills, etc. In addition, I'm not planning on flying through much acetone.
  • It's "tough enough". It's not as tuff as Akzo, but protects nicely.
  • Cures quickly. I can turn parts while painting in about 1-2 minutes. I can dimple after 36 hours at 70 degrees and 40% humidity.
  • It's a nightmare to mix in it's own container. When trying to mix in it's container, you end up with a blob on the of a stick.
  • Consistency out of the can makes for a lot of waste when doing small batches.
A few hints use:
  • Purchase a couple of quarts. Then buy a gallon can and use a can opener to cut the bottom out of the EkoPoxy quarts and put the contents into the gallon can. Much like getting dog food out of a can. You'll end up with a half gallon of product in a gallon can. Makes mixing a breeze and minimizes waste.
  • When mixing, you'll need to add some water. The 5:1:1 ratio has never worked for me. Remember, EkoPoxy is waterborne NOT water based. This means that the paint "rides" on the water molecule and then effectively splatters when it hits the surface. Water does not reduce/dilute the molecule itself. I'm thinning to roughly 5:1:1.3.
  • Works well with the 3M Accuspray gun/system
  • I find that 1.4 mm tip with 12 psi at the cap works extremely well for spraying.
  • If you're getting orange peel, my opinion is that the primer is too thick.
  • Mix the paint and the distilled water at the proper ratio first, then add the catalyst at the proper ratio (5:1:1). If you're going to add additional water, do it after the paint has been mixed at the proper ratio.

Being easy on my body is my primary reason for use. I'd hate to get this contraption finished only to find out my health has deteriorated. I also love the way it sprays when mixed properly. Although my verbiage above makes EkoPoxy sound as if it's not very tough, the fully cured product is quite hard and impressive. I'm not sure why we all use acetone for a test, try MEK on some Akzo and see how it does. Short version: we can nearly always find a chemical that will cut paint.

The above is what works for me. Your mileage may vary.
Dues Paid for 2022
Emp Complete (including fiberglass)
Wings complete (including fiberglass)
Fuse Complete
Finishing Kit Complete
Avionics Complete
Working on FWF
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Old 09-02-2019, 06:50 AM
Larry DeCamp Larry DeCamp is offline
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 1,273
Default Thoughts on primer

I was told that the value of epoxy primer was its Corrosion resistance, not toughness. Ie. Two part finish coats are just as scratch resistant as epoxy. Not suggesting this, but I used the white single component primer and urethane gray on the interior and it is really tough. The primer is like milk, no mixing, you can save what you don't use for intermittent spray sessions.
Larry DeCamp
RV3B sold
RV-4 fastback in process w/ Superior roller 360/AFP/G3X/CPI/Catto3b
Clinton, IN
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Old 09-02-2019, 08:24 AM
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sprucemoose sprucemoose is offline
Join Date: Jan 2005
Location: MKE
Posts: 1,563

Originally Posted by Reflex View Post
[*] Mix the paint and the distilled water at the proper ratio first, then add the catalyst at the proper ratio (5:1:1). If you're going to add additional water, do it after the paint has been mixed at the proper ratio.
I agree with most everything you wrote but this stuck out at me. This is contrary to Stewarts directions and to my own experience. The exact mixing ratio will depend on the product, the gun, tip and to some extent the user preference, but I've never heard of adding water first. I do agree that in general the Stewart's mixing ratios leave things a little thick for my taste.

I'll admit that I never tried it, but in general it is best to stick with Stewart's recommendations.
Jeff Point
RV-6, RLU-1 built & flying
ATP, CFI, Tech Counselor, Flight Advisor & Past President- EAA Chapter 18
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