Help with UV Clear Solvent Pop

nokin

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I need some help solving my solvent pop issue with UV Clear with very slow activator. I've been spraying with this combination for about 3 years with great success.

Last week, for the first time ever, I started getting solvent pop, but only in the first coat. If I wet sand with 1500 to get all the bubbles and craters out then clear again, there is no solvent pop.

I've tried spraying over solvent base, water base, and even an unpainted speed shape, and the results are all the same, solvent pop only in the first coat. Every subsequent coat comes out fine.

I'm stumped, hoping someone can give me some insight, thanks!
 
I'm stumped with you as solvent pop normally happens in 2, 3rd coat.
Only two ideas.
Do you have a desiccant system or a refrigerant system on your compressor?
Only other thing are you using W&G remover on the base before clear.
 
Hi Barry, no desiccant system or a refrigerant system, only 2 moisture traps, one at compressor and one at the wall. There is barely any water in the second trap.

And I've tried both with and without wax and grease remover, same result.
 
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My tiny pinholes problem ended (knock on wood) when i stopped using other brand reducers.
I don't spray often so washing out gun with spi reducer is no bigge.
I use very slow activator & medium reducer.

You also mentioned craters..happened to me using top shelf of a major brand reducer to wash gun a couple summers ago.
 
Are you using an old open can of activator? If it has absorbed moisture you will have all kinds of problems.

Don
 
Are you using an old open can of activator? If it has absorbed moisture you will have all kinds of problems.

Don

That was actually one of the first things I thought off, even though I use bloxgen everytime I open and close the activator. A brand new can of activator did the same thing.

What has me confused is why it is only in the first coat, and it happens on solvent, waterbased, or unpainted.

Just got a desiccant dryer, I hope it solves the problem!
 
Solvent pop on first coat is limited to only a couple of things and I believe you are getting vapors through the air line, so your new system should solve that problem and never use W&G on base before clear unless you had to make sanding corrections and give it time to get out if you do.
 
Welp, I'm out of ideas. Installed the desiccant dryer and still getting the same solvent pop in the first coat.

What else can I try? Retarder? Reducer? I'm already using very slow activator, but maybe the heat and humidity in southern california right now is causing it flash too quickly?
 
You haven't mentioned what sized needle,what kind of air cap (conventional,RP, HVLP), what pressure you're using,booth conditions, spray distance,the name of your dog,how long are you letting the base flash.
There's just so many factors that could affect things.
 
you know i had a crazy solvent pop/fisheye issue many years back. took me months to figure it out but it ended up being my mixing cups. it would not show in primer or base i guess because they are either too thick or flash too fast but when ever i mixed clear in these cups i would have the problem. got rid of the cups and never had another problem since. not saying its your cups but it really could be anything bizarre like that. if your using 2.1 voc uv clear reduce it 10%. i know many 2.1's are thick and dont atomize as well and you will get air entrapment which ends up looking like solvent pop or cloudy areas but its micro bubbles. almost every 2.1 i ever used always required a 10% reduction even if its not in the tech sheet.
 
I think I may have found the culprit, it's a faulty pressure gauge at my wall regulator. It's reading 5 to 6 psi lower than it should and was over atomizing the clear. Was cleaning the filter in the water separator when I decided to check my gun with a regulator attached as I usually spray without one, and it was way over what I used to spray at.

I spray small parts and use a mini gun, the devilbiss gti pro lite with a RP 1.2 tip. Dropped the pressure at the wall 6 psi, and problem was gone! At least I have all new air hoses and a desiccant dryer now = )
 
Guess I spoke too soon, problem is back even with the correct pressure at the gun. I'll try your suggestion Jim C, hope it works!
 
Take a gallon can like a reducer can with one side of bare metal showing, DO NOT CLEAN or SAND, spray one wet coat with gun 5" away like you want it to run but one coat only.
DO NOT do a second coat and tell us what it did. A picture is best of course.
 
I'm subscribing to this thread because it's a really weird problem, and I'd like to know what the fix is when it's discovered.
 
Agree, very weird and not real common for clear to do this in the first coat.
Reasons I know it.
Excess solvent in base as not had times to flash (unlikely)
Washing base with wax and grease remover and not out of base yet.
Co2 gassing caused by moisture in the air line.
Spot fisheyes.

I'm out of answers but the can spraying will get us to the right area of the problem.

Epoxies are a different set of issues and only talking about clear.
 
i mix in straight sided containers . i've had far too many mixing cups that were kaka for mixing a full qrt .
 
Okay, here are some pictures of the gallon can sprayed. Using a Devilbiss sri pro lite with the RP cap and 1.2 needle at 29 psi, full fan and fluid was 1/4 turn in from wide open. 1 single pass over an uncleaned and not sanded gallon container.

The pictures as uploaded:

IMG_0919.JPG IMG_0921.JPG IMG_0926.JPG IMG_0927.JPG IMG_0928.JPG

1. 30 seconds after it was sprayed
2. 5 minutes after, you can start to see bubbles forming
3. 15 minutes, even more bubbles, the ones around reflection of the lights are ones that have popped
4 and 5. 10 x magnification of the bubbles.
 
No, if's or buts about it, that is a co2 gassing, water from the airline or over atomizing the clear to much with the 1.2 and cramming humidity into the clear.
And what you are seeing is Isocyanate clumping where the tin is forcing too much moisture into the isocyanates.

What ever the cause is from the 2 listed first thing I would do is the same test with a 1.4 as bad as it looks I would say that will take care of the problem but if it does not then we need to look at compressor filtration and perhaps not wetting the floor, this is why we recommend a 1.4 tip.
 
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Hi Barry, the gun I use is a mini gun, would a 1.4 be too big? I thought a 1.2 on a mini gun would be sufficient, as I've been using the same gun / compressor setup for the past 3 years without a problem.

Would adding retarder help?

And out of curiosity, how come this iso clumping only happens on the first coat, and not the ones sprayed on top of it?
 
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