Nibs or Solvent Pop in Flow Coat

S

strum456

Oldtimer
Why do I always get little specks all over when I flow coat?

About a week ago I sprayed 3 coats of UV clear. I sanded it out this weekend with 400 and 600. Yesterday I washed the parts with Dawn. Then I went over them with 700 in a spray bottle. Tonight I tacked them off at least 2x. I was super cautious about dirt on me and on the gun, as I just had the same problem with a batch of parts a few weeks back. So anyway, I hit the first panel with clear, and tiny little specs all over. It looks like solvent pop, but how would it be? I'm using slow activator. Metal temp is 70 or so.

These "specks" easily sand out with 1500 or even 2000. Once sanded and buffed, everything looks perfect. Whatever it is, it's causing me extra work.
 
Exact same thing happened to me yesterday in my jams. 3 coats of UV, dry a few days, wet sanded, then flow coat with slow activator and tiny specs all over. I wet sanded again today, then sprayed two more coats without reducer and no specs, but some orange peel. Looks like I'll be wet sanding and compounding the jams.:eek:
 
DATEC said:
could it be overspray in the air falling down lying on the surface? how is your exhausting?
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I could see the specks immediately. I don't think there would have been time for anything to settle. I went out and sprayed a second coat after I made my first post. Some of it disappeared with the second coat. I'd really like to pin this down. I never get anything that looks like this on a first clear session. I've seen it quite a few times on a second session though.
 
Solvent Pop generally happens in pretty specific situations, temperature has to be high (95+) along with correspondingly high humidity. Usually happens when spraying clear and it is noticeable because as you are spraying you literally see a bubble pop on the surface. I would be suspecting some sort of contamination whether it's airborne or in your air lines. If it's even throughout look for contamination in your air lines.
 
After coser inspection this morning, it really does look like solvent pop. You have to look very close to see it, but there are tiny specks everywhere. Vertical and horrizontal surfaces are the same. Is there a type of contamination that would show only when spraying clear on clear? If I spray clear over base, this never happens.
 
This is going to sound strange, but I have had problems similar to that with flow coats, and also it seems very sensitive to any surface contamination as well. What I do now is start with clear that has been overreduced 50%, and put ONE coat of that on like a coat of base. Then wait 30 minutes and proceed with the flow coats. This has greatly decreased my risk of problems with flow coating, and it doesn't seem to make any difference in the final gloss or texture. Maybe it adds an imperceptible amount of texture, but I can't tell.
 
Same here, I assumed it was solvent pop. I stopped reducing UV clear for flow coat. I just spray it 1:1 even for flow coat, I just use a couple steps slower hardener. Hard to do in August in SC....
 
crashtech said:
This is going to sound strange, but I have had problems similar to that with flow coats, and also it seems very sensitive to any surface contamination as well. What I do now is start with clear that has been overreduced 50%, and put ONE coat of that on like a coat of base. Then wait 30 minutes and proceed with the flow coats. This has greatly decreased my risk of problems with flow coating, and it doesn't seem to make any difference in the final gloss or texture. Maybe it adds an imperceptible amount of texture, but I can't tell.
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Crash,

What gave you the idea to do that? If it works for you, I'll certainly give it a try.
 
Bartman said:
Same here, I assumed it was solvent pop. I stopped reducing UV clear for flow coat. I just spray it 1:1 even for flow coat, I just use a couple steps slower hardener. Hard to do in August in SC....
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No reduction. I never use anything but slow activator.
 
strum456 said:
Crash,

What gave you the idea to do that? If it works for you, I'll certainly give it a try.
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It's a procedure I came up with (with Barry's help) to avoid fisheyes in the flow coat, but I thought it might be worth a try in your case just in case your issue is something to do with the surface or surface prep.
 
be sure your activator is not old. if been opened before and you didnt put some inert gas in it before replacing the lid the activator will get moisture in it and look a lot like solvent pop or fish eyes either. i've had both to happen before
i spoke with barry and figured out what was going on. old activator can cause lot of problems if you dont flush out can with inert gas before storing. just my 2 cents
 
yes that is what i use. just a couple seconds is all you need unless can is getting low i never use more than 4 seconds though.
 
The activator isn't more than a month old. I don't do the inert gas thing, but I don't generally let activator sit around.

Good tip though. Thanks
 
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strum456 said:
The activator isn't more than a month old. I don't do the inert gas thing, but I don't generally let activator sit around.

Good tip though. Thanks
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Depending on how empty the container is and how many temperature cycles the container has been exposed to one month is long enough for the activator to absorb moisture....

Don
 
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