Stewarts System Paint Problems

[Mruffatto]

Hello all,
My buddy and I are really struggling with the stewarts system ekopoly paint. We are painting a kitfox. I was planning on using stewarts on my bearhawk but I'm really having second thoughts. Solvent pops is our problem. We've tried changing as many variables as we can ie gun settings, tack time, spray technique, mixture etc. No matter what we do we never get a definitive difference. We can get good color saturation and gloss but always end up with some popping. We've looked under a microscope and it looks like a little volcano. We are painting in an inflatable booth, temps in the mid 60's, low humidity, recommended gun, large compressor. We've talked with Andy and another painter at Stewarts and they reassured us our setup should get better results. All while wasting hundreds of dollars of paint and time.
So I'm wondering if anyone has had this problem and successfully figured out what to do different?
Thanks,
Mike

[Chewie]

Mike,
I have not experienced this but find it very interesting. You tried changing several variables, did that include different air pressures? A good tack, light coats with ample dry time between, and higher pressure solved a lot of initial issues I had with ecocryllic on ecoprimed steel. Mid 60s seems a little cool for Stewarts but still doable if your mist is atomized. My 2¢.

[TimTall]

I had similar problems at first with Stewarts System. More time between coats solved the problem. I was waiting almost an hour before the final wet coat by the time i had it figured out. I had the temp in the booth at minimum 70, probably closer to 75 most of the time too,

It's still not an automotive quality paint job but it's pretty good. I was aiming for it to look good from 6' but it's closer to a 3' paint job.

[whee]

I was told the same thing. If the follow coats go on too soon you get solvent popping. Stewart’s is definitely different than anything I had sprayed before but i like the rest of the system so much I’ll use it again. Plus the paint is practically bulletproof once cured. Once I figured out how to spray the paint I thought it looked really good.

[rodsmith]

Not an issue I have ever had. I do wait longer between coats than Stewarts says is necessary. I follow the recommendation of the previous coat not transferring color to a bare finger before spraying again, which for some reason is longer than when color stops transferring to a gloved finger.

[AZBearhawk272]

I had a similar experience with tiny bubbles / pinhole popping. I am spraying in dry warmer Arizona.
After mixing catalyst wait at least 30 minutes for the paint to fully induct and then thin, I went a little thinner than recommended, faster quicker tack and application coat, longer dry between coats and popping was not an issue. Too much, too soon = popping........

Kevin D

#272 KCHD

[Battson]

A friend painting a Super Cub had all kinds of problems because the Stewards paint had expired (past shelf life). Unsure if this was anything like your problem, ultimately the paint peeled off spontaneously some months later, no paint stripper required... I would suggest the shelf life must be respected for Steward Systems paint.

For comparison, I find you can practically ignore the shelf life for Polyfiber products. In some cases I have doubled the calendar time and they still work great. Nasty MEK based paints may be a little more resistant to aging.

[robcaldwell]

The only problem I ever had using Stewarts was my own fault.

1). I did not etch my wing struts properly. I can take my finger nail and the paint will come off. I will re-do those at some point.

2). I painted my right wing when it was too cold. It has some orange peel.

My paint went on very well and I attribute that to having the right equipment, which Stewarts insists, and sounds like you did too. High capacity compressor, high flow lines, DeVilbiss paint gun, Air Dryer, etc.

But I do believe the key to Stewarts is increasing the wait time between coats. I don't think that is an issue with solvent based paints.

[Bcone1381]

Another viewpoint to builders should consider is the possibility of surface contamination. I'm sure you are familiar with this document from Stewarts that I linked to below. Bullet point number three demands shooting Stewarts with new clean non-silicone air hose to avoid contamination.

Silicone contamination is a concern for me. My wife uses dryer sheets in our household clothes dryer which all have silicone in them. So, I only use brand new rags in the shop to avoid all silicone contamination. My understanding is that the dryer drum can spread silicon contamination onto rags even without dryer sheets being used in the load.

https://stewartsystems.aero/wp-conte...structions.pdf

[BradW1062]

I know this is a year behind, but it came up in the search for Stewart Systems, and I am very curious.

Mruffatto, a couple of questions:

First, what do you (and others) mean by "solvent popping"? There is no "solvent" in SS paint, it is water-borne - so where does this come from? I am assuming you are talking about what we used to call "fish-eyes"? Where a small pin-hole like crater forms that is completely free of paint? I am assuming this is different from just an air bubble that pops, right?

If so, then I think that is most likely due to oil contamination, in this case anything oil-based that is immiscible with the water in the paint. I know another fella that had this problem years ago when this system first got started. Any oil, whether mineral-based, synthetic, silicone, even the natural oil in your skin from handling the part, can cause this problem on water-borne paint. And you never know where it will be. Like Bcone1381 says, even dryer sheets and fabric softener in your clothes can cause it. It is difficult to remove, especially in the air supply since compressors and some of our tools are oiled on purpose, and depending on where that oil goes in it can "contaminate" everything downstream. Getting an exceptionally clean oil-free air supply can be a hard thing to do. I fear this problem, and it is one of the reasons I am considering abandoning the SS product. I had started with them on my Bearhawk back in 2008/09, but now that I am finally getting back to it, with covering approaching, I need to find out if it's still a good method. Even though I may use their glue, I may not use their finishing coatings. Trying to figure this out beforehand...

Second, have you had any luck since the original post? Did you figure out what to do to stop this? I had used acetone to wipe down the parts that I did (seats, rudder, elevator) before EkoFill, and I didn't have any problems with that - but I haven't finish-painted anything yet.

[TimTall]

I used Stewarts System with good results. I had some solvent popping in the first parts I did because I wasn't waiting long enough between the 2nd to last and last coats. You've got to let it get to the point that it's almost dry to the touch before the final coat. Once I figured that out it went very well. I did it in my garage with a cheap compressor that had the minimum recommended output. I did use the biggest fittings I could get on my air line and minimized the length of hose. I made an air dryer for the air which was definitely critical, especially in the humid weather I was painting in.

The water is the solvent in water based paints isn't it?

[BradW1062]

Tim, thanks for the reply - good to know that is worked for you. I can see that maybe this is some kind of bleed through from the first coat? I do remember the manual saying that the previous coat had to be tacky but not where it could be lifted with a fingertip. Maybe if it isn't, then the remaining water in the first coat builds up and "pops" through the next coat?

The water is the solvent in water based paints isn't it?

Well, I guess that is sort of a matter of semantics in some ways - but no, I don't think it is. The water carries the paint polymers, which then cross-link as the water evaporates, allowing them to come into closer contact. But it doesn't dissolve and thin the materials like a solvent does in your traditional non-polymer paints like dope or lacquer or something. I was meaning by my statement that there wasn't any lacquer thinner, mineral spirits (naptha), MEK or anything like those traditional solvents in the Stewart Systems coatings - so it really is not "solvent" popping, right? I don't think that is proper use of that term in this case, so I am questioning it. Is it "water popping"? Maybe, but I've never heard of such myself, that's why I am trying to see what this is about.

[SpruceForest]

Have done a lot of water-based finishing, and agree that surface and equipment contamination is a constant battle... to the point where we ran a second downstream filter and regulator for our HVLP conversion guns and separate guns for the turbine systems. Fisheyes are usually due to either silicone or other oil mist on surface or entrained in the airstream altering local surface tension... lacquer is a little more tolerant than other finishes, and WB stuff is absolutely intolerant. A supposedly clean-but-still dirty gun will also do the trick... especially if some idiot shot lacquer with fisheye eliminator added prior to understanding what fisheye eliminator might be made of (hint... all that stuff is is yet more silicone to more uniformly reduce coating surface tension). FWIW, we run good quality PVC or urethane hoses and clean the end fittings of manufacturing gunk prior installation and use. Guns get cleaned with full disassembly prior to use and regularly thereafter. Even the 20 ounce Harbor Freight HVLPs we toss after epoxy primer duty (cheaper to toss than clean at $8 per) get disassembled and cleaned prior to use.

[rodsmith]

I followed Stewart's instructions/cautions religiously and never had any issues. To get the required volume of air you will probably be using an oiled compressor.. I constructed a water separator like detailed at the Stewart's seminar at Oshkosh. I also used a Devilbiss filter separator to remove entrained oil and water It wasn't cheap and I had to replace the media a couple times at $50 a pop but it worked perfectly. Also its important to paint within the detailed temperature/humidity limits.

[Bcone1381]

I followed Stewart's instructions/cautions religiously and never had any issues. To get the required volume of air you will probably be using an oiled compressor.. I constructed a water separator like detailed at the Stewart's seminar at Oshkosh. I also used a Devilbiss filter separator to remove entrained oil and water It wasn't cheap and I had to replace the media a couple times at $50 a pop but it worked perfectly. Also its important to paint within the detailed temperature/humidity limits.

I concur with everything Rod said. I also concur that drying the air gets attention. So I get the filter "Best Practice" attention after every painting event....like a single wing being painted. (I wont go two wings)

I dissected a DeVilbiss filter from the filter dryer I show below. The bottom black part detaches to expose the $50-60 filter. After melting two filters trying to dry out the air inside the cartridge I changed my approach.

I got the top of the filter off with some (but not excessive) effort. Inside are two very simple discs; (I will call the disc an air filter the thickness of a nice paper napkin) one on the top and one on the bottom of about 1.5 cups of silicone beads. I dumped out the silicone into a cake pan, then heated it up for an hour at 225F in my turkey roaster. I temper the heat from the bottom of the roaster using small thin wood scraps to form a 3/8" airspace under the cake pan. After baking, I let it the beads cool then reassemble the filter element with the airfilters in place. The top will pop easily off now, so be careful when you re-install it.

If your like me you'll destroy (this is the education part of building) your first one, buy a new one, then get it right on your next attempt.

I also put a dryer, very inexpensive ($40), from Amazon, to catch some of the moisture prior to entering the QC3. I also have about 80 feet of copper tubing between the compressor and the first dryer with numerous water drain valves at every low point in the air delivery plumbing. These get emptied every day before I start painting.
Screenshot 2024-01-28 at 12.48.07 PM.png Screenshot 2024-01-28 at 12.50.53 PM.png

[BradW1062]

Thanks for the responses, guys!

I talked to Marty at Stewart Systems, and he confirmed that what everyone is calling "solvent popping" is the remaining water in the first coat (or two) accumulating and "popping" through the second (or finish) coat. He said that waiting long enough for the water to flash/evaporate enough that the first coat is tacky, but does not transfer to a knuckle-touch, is the right way to apply the paint, and will prevent this. That rushing the coats is the typical problem that leads to this. Of course, temperature and humidity level in the paint booth have a big effect on how long this takes, so your results my vary.

I had never heard of this problem before, and didn't have it myself back in 2008 with the little bit I used SS, probably simply because I didn't rush the coats, and pretty much followed the tackiness guideline. Didn't know why at the time, but it worked for me. And my previous experience 30+ years ago painting cars, etc., is that the solvent left in the first coat would "dissolve" into the next coat, or with lacquer the thinner in the second coat would slightly dissolve the first coat and you often used retarder to give it time to do this better so it would flow out. So I have never really experienced the solvent popping thing that I can remember, or have ever noticed. But then I haven't worked with these "new" epoxies or catalyzed polyurethane paints or water-borne paints much either.

Also, I talked to Marty about the filtration and such and it seems that diligence in keeping your hoses and equipment clean and free from cross-contamination with air-tool lubricants is key. Jus tas others have mentioned, keeping dedicated hoses and filter systems for the paint equipment is important. At this point I don't know if I have an oil problem or not. My compressor is new, and has a built-in aftercooler and an automatic tank drain to remove most of the accumulated water. I have a Parker-Watts QIX Filter-Regulator-Lubricator that I have had forever, and I removed the lubricator years ago. This system has a polypropylene conical filter element a lot like the QC3 filter that Bcone1381 posted above. I did find that I (may) can get a coalescing filter element that is supposed to be much better at removing any atomized oil, so I am on the search for that. Marty said that keeping dedicated hoses and such and using a good water-separator/filter system should be all you need to do.