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Finally getting good results with Stewart

andrewtac

Well Known Member
I am building a 10, and wanted to paint as I go. I also am trying to get away with painting outside (no booth) with just a 3m respirator. I painted my mustang years ago, did the priming outside and ended up renting a booth. It turned out nice, mostly due to prepping the primer well and wetsanding the finish. Painting outside, I expect to get some bugs and dust but plan on wetsanding either way.

Anyways, I wanted waterborne to reduce the VOCs, I also wanted single stage for simplicity of repairs and doing a little at a time. I am not painting a show plane, I want it to look decent and hold up. I ended up picking Stewart.

Last paint I used was traditional BC/CC sherwin (not waterborne). It was a learning process, but came pretty quick. Stewart does not lay down like what I have used in the past. The primer nor the topcoat. The primer is more difficult to spray well than traditional BC/CC topcoats, at least in my experience; and the Stewart topcoat is even more difficult than their primer. However, neither take a PhD in painting, just some practice. Watch the videos numerous times, really think about what they are saying, and what to expect.

I would recommend the finishline gun, as I found known settings; this helped. Use a paddle in a drill to stir, don't shake the can.

My first attempt at spraying primer, I ended up with a really rough spotty finish. I prepped the metal according to them, but didn't spray according to them. I sprayed just like the AZKO I started with. Just tired to lay it down. Next time I did what they recommend, fog or tack coat, then laid down paint. Much better, however I tended to make more runs than desirable. What I ended up figuring out later was I needed to adjust the needle. I had the needle wide open and used distance from panel and speed of gun to regulate the spray onto the metal. This sort of worked, and I had good result sometimes; usually ended up with runs.

Top coats. I was really excited to spray the top coat, I start with some small panels and emp fairing. Well again the needle was full open. Results were horrible, ran like a race horse. When the white top coat runs it tends to bubble and the bubbles seem to propagate back to the primer. The bubbles are tiny, almost looks like intense solvent pop (and I think this is what it is). These runs are almost always not repairable, you end up sanding past the coat into the primer to get rid of the bubbles. So several re-attempts, still using my technique of speed and distance to regulate spray amount; never really worked. Finally, I did some googles and realized folks were starting with the needle almost all the way in, and backing it out a little at a time for each fog coat and final wet coat. I don't remember seeing this in the videos, and don't really remember doing this when I painted BC/CC; but I was at a rented booth and had help (they might have done this). Anyways, what I found was start at 3/4 needle out, move up 1/8 of a turn each coat to end up at 1&1/8 out for the 4th and final coat (wet coat). These settings seem to work really well for me, no runs doing this. I think I could maybe go 1&1/4; but no runs after a week of sanding off runs and multiple attempts makes me happy. Another important thing I found was the previous coat needs to be tacky but no longer transfer paint when touched. This was something on the video I ignored and just timed about 5-10 minutes. Some coats have taken up to 30 minutes to not transfer paint, 5-10 minutes doesn't work. I have used these things I've learned and the primer sprays well too now. I usually only do two fog coats, and open the gun a little more; also the fog coats dry quickly (no paint transfer to touch) compared to the top coats.

Bottom line, must do light coats building up to a wet coat, coats must be tacky but not transfer paint, and start gun at 3/4 needle out and adjust 1/8 turn out on each coat to spray final coat at 1&1/8.


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Since you are on the other side of town, have you been painting in this Texas heat and humidity? I waiting for the 2 days of fall to do it but I’m itching to get my interior painted.

Jay
 
Since you are on the other side of town, have you been painting in this Texas heat and humidity? I waiting for the 2 days of fall to do it but I’m itching to get my interior painted.

Jay

Absolutely, I asked them in an email and they said it doesn't hurt it, it does better with humidity. I think the spec sheet says up to 70%. I have painted higher. However I do have AC and dehumidifier in my hangar, once I put the wet coat on I bring it in the hangar. I almost got hit by a scatter storm this morning, got inside just in time. I do tend to try to paint in the morning or late afternoon, when it is a little cooler and the wind is down. Also, helps me avoid direct sunlight.
 
Thanks for posting your experience. Couple of questions. How long for the paint to dry so that bugs/dust aren't a problem? Do you know what air pressure you are using at the gun with the trigger pulled? Are you spraying with the fan full wide open?
 
23 at the gun, full fan, I have started removing dust and bugs with a pint free and some 91% alcohol. Not sure if this is better than just sanding them out as it does remove some paint. I do this between coats once the paint doesn't transfer. I don't know how long before it is dry enough to not take in bugs or dirt, I'd imagine at least half an hour after the wet coat maybe an hour.
 
Cut & buff

23 at the gun, full fan, I have started removing dust and bugs with a pint free and some 91% alcohol. Not sure if this is better than just sanding them out as it does remove some paint. I do this between coats once the paint doesn't transfer. I don't know how long before it is dry enough to not take in bugs or dirt, I'd imagine at least half an hour after the wet coat maybe an hour.

Try Cut & Buff on a test piece. Usually it's best to wait till the paint is cured. I have no experience with water based but I cut and buff urethane the next day. 24 hours. Add a coat if you plan to cut and buff and stay away from corners and edges. Super easy to break though the top coat.
 
Try Cut & Buff on a test piece. Usually it's best to wait till the paint is cured. I have no experience with water based but I cut and buff urethane the next day. 24 hours. Add a coat if you plan to cut and buff and stay away from corners and edges. Super easy to break though the top coat.

Yep this is what I am doing, love the way it makes the paint look. I am not cutting as much as I would on BC/CC, and not adding another layer of paint. The Stewart lays down thick, and like I said I am not getting over aggressive with it. I usually wait about a day before I start the process. 1000,1500,2000,3000 then 3m compound, fine, ultra fine.
 
I have a love hate relationship with stewart systems. If you follow their technique and have the right equipment then it can lay down a smooth and glossy coat. Its also durable and holds its gloss for a really long time. The key is to have a ton of air; >15SCFM @90psi and use the devilbiss finishline gun with the recommended tip size.

Regarding technique, I used the following method:

After priming, sanding, cleaning etc in preparation for topcoat youll coat each part with 4 top coats. The first 3 coats are fog coats and the final coat is where you lay it on thick enough to flow out, adjusting the flow needle accordingly. The key is to start the next coat as soon as the tack develops at the start of your previous coat. The last coat is where you lay it on thick - the goal is for the gloss to develop a few inches behind the gun. I painted my RV-3B and later my sons pedal plane in stewarts smoke grey. The metallic green trim color on his pedal plane turned out really really well.

pedal-plane-front.jpg
 
I have a love hate relationship with stewart systems. If you follow their technique and have the right equipment then it can lay down a smooth and glossy coat. Its also durable and holds its gloss for a really long time. The key is to have a ton of air; >15SCFM @90psi and use the devilbiss finishline gun with the recommended tip size.

Regarding technique, I used the following method:

After priming, sanding, cleaning etc in preparation for topcoat youll coat each part with 4 top coats. The first 3 coats are fog coats and the final coat is where you lay it on thick enough to flow out, adjusting the flow needle accordingly. The key is to start the next coat as soon as the tack develops at the start of your previous coat. The last coat is where you lay it on thick -

That’s very close to what I ended up doing. Except I think I did closer to 8 tack coats (well 4 but alternating patterns) and no top coat. The paint is super weird stuff and moves around for at least 15 minutes after it is sprayed. The paint you lay down is not the paint you end up with!

When I followed their videos I got a really nice looking top coat that slowly fell off the wing. Massive amounts of runs and sags. We didn’t notice until it was too late and ended up having to rip the fabric off and completely redo the wing. Went easier the second time and checked it earlier and it still wanted to fall off the wing! Ended up saving that one with a wash down before the paint cured. I think it took at least 4 more tries to get something that worked reasonably and consistently.

It’s also just about the smelliest and stickiest paint I’ve ever sprayed!
 
Isocyanates ?

Just a reminder, waterborn paint makes tree huggers feel all better, but 2k paint still requires an appropriate respirator for you !
 
I painted with Stewart Systems 5.5 years ago and it has held up well. I thought "water born paint wont bother me" but I was wrong! I started with just a respirator. After a day or two my eyes turned red and burned like crazy and my ears blistered and actually started peeling! I quit for a week or so to get over this and acquired more protective equipment!
 

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I think spraying outside I am ok with the respirator. Unfortunately there is almost always wind when I paint. Makes it harder but cuts on the fumes. I wouldn't spray inside without more. I did have a full mask, but I ended without eye covering. I might go with some goggles.
 
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