Stewart Systems EkoPrime, Topcoating

Bartman

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#1
Always check revision dates to be sure you have the most current information! :)

EkoPrime Instructions sheet
https://stewartsystems.aero/wp-content/uploads/EkoPrime-Instructions.pdf

So, I messed up and figured what better way to take my medicine than to tell everyone about it!

The instructions above say that EkoPrime can be topcoated after a few hours. In the larger Stewart Systems manual it says that primer that has been allowed to sit for more than about five days must be sanded and then cleaned before being top-coated.

I woke up Saturday with that feeling that it was time to paint. No more sanding, no more patching, no more delays, just perfect weather and time to go. Areas of the existing white paint were uneven due to sanding to remove goose bumps and runs in the finish. There were also a few small patches that had been sealed with the darker gray EkoFill (UV protection plus weave filler) so they needed a lighter gray primer coat so they wouldn't be as visible under the white top-coat.

My plan was to apply the EkoPrime more heavily on the bottom where the paint was very thin and then lighter around the sides of the fuselage and on the gear where we just needed the variations to be muted out a little. It was about 83 degrees in my garage with the fan on pulling in fresh air.

Where the primer was applied more heavily it laid out better, where it was thin it left a rough surface, the warm temps probably had a lot to do with that. My conversation a few weeks earlier with Andy from Stewart Systems led me to believe that the results might not be quite as glossly and smooth without sanding but that I should be ok so I had planned to wait about four hours and go straight to the white base coat of EkoPoly.

I'd like to say the results were mixed but I should have stopped to sand and clean the primer before moving to the base coat. I've got spots where the white is glossy and smooth and spots where it's still rough like very fine sandpaper. Aircraft left is all pretty good, aircraft right is not good enough so I've got to sand the roughness out, clean it and repaint it.

Overall the primer is great to work with, it gets diluted with up to ten percent distilled water and sprays very nicely. The EkoPrime primer is compatible with both fabric, metal, and fiberglass. It isn't resistant to solvents so solvent based top coats aren't compatible.

Like other Stewart Systems coatings, you spray light base coats to develop the proper rough surface while also building color. The roughness of the first few coats helps the heavier final coat to hang on and stay stuck. If I were doing this again I'd still have varied how much primer I used in different places but would have scuff sanded everything before top coating so I'd be moving on to trim lines today instead of more sanding! Doh!
 

Bob Turner

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Apr 4, 2018
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#2
My buddy Ed is having the same problems with his Cub. My impression is that if you shoot the Poly on a dead-smooth surface you get better gloss, but I will never know for sure. It is either Ceconite/dope or Stitts for me.
 

Bruce

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Dec 22, 2018
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Knoxville TN
#4
Thanks for sharing I did go to the paint class at sun and fun, I made great progress at first and have everything ready for fabric except the fuselage, then I had to put the whole project off for the last four months. Now I’m hoping to get started on that mid next month with covering the fabric scratching my head about putting it in primer and then storing those parts and working on the fuselage so I can paint it all basically one time. Will any of the paint surface show in photos if so would you consider sharing those. Do you think the sandpaper like surface is because of the heat coming up during the day and the pain trying to quickly do you think it was the thin primer coat?
 

Bartman

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#5
IMHO, it was a combination of the warmer temps and the thin coats. if slightly heavier fog coats had been applied they might have laid out a little before drying.
 

Bruce

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Knoxville TN
#6
Ok in the class I thought lighter fog coats allowing to be tacky to the touch till color saturation then the last coat was heavy for the gloss. I guess I need to re read the instructions and will make a test panel to Learn on
 

Bartman

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#7
@Bruce

Light fog coats are the best, the goal of the fog coats is to slowly develop the color while creating the right texture for the top coat to stick to. If you get too aggressive with the fog coats you'll develop slight orange peel and then you either have to stop to let it cure so it can be sanded out or you just live with it. I got a little of that in my red top coat because I went too aggressive with the second fog coat but it's not bad so i kept going.

With the primer, I went really light with the fog coats trying to just obscure the colors of the old paint job. Looking at my N-numbers visible under the red top coat it's obvious now I should have put more primer on. I'm kind of leaning towards figuring any primer coats will have to be sanded out before top coat but I'm not even sure that's true, it would depend on whatever you've got for texture once the primer dries, it might be different for everyone. Mine was definitely too rough to be topcoated in a lot of the places where I sprayed it on the fuselage.

It's possible if you do two or three fog coats of primer and then a heavier coat the finish will be suitable to paint over without sanding. I don't recall what I had with the wings when they were primed, I think the plan was to sand them regardless.