On to spraying the colour coat now, things aren't going too bad, bit of orange peel but it looks factory that way. However, I am having a problem with tiny bubbles in the paint. As soon as it hits the panel, tiny bubbles appear. It seems to be mostly located where I have put more paint on, but still it is all over the panel. I'm pretty sure they are air bubbles rather than a reaction/contamination as the panels have been thoroughly prepared.

I'm using 2K but with a non-isocyanate hardener (Valspar Unibinder). This worked ok with the primer, but did need significantly more thinning to go on properly (35-40%). So I've thinned the topcoat paint down a similar amount. I'm using a 1.4 needle too and the envurionment is well controlled for heat and moisture. I have several theories to the problem I'm having

Too much pressure - the gauge says around 60, but when I pull the trigger, it drops to a more respectable 40ish. Regarding this and the recomended pressure, should the gauge read 43psi (the recomended peressure) with the trigger open or closed? The increased pressure is causing aeration of the paint.

Paint too thin - again, allowing aeration to occur

Solvent pop - caused by too much thinners/paint being put on to thick

Moisture/panel wipe trapped under the paint - the bubbles look like microblisters, but with the 'dome' still intact. Just wondering whether the porousity of the primer may be holding onto moisture. I did thouroughly dry the panel over a heater but could this still be a cause? The heater was so warm, I could see the moisture receding across the panel

Or could there be another reason? I've never sprayed with an HVLP gun so I'm still learning, or the Unibinder. When I used my traditional suction gun with proper 2K i had none of these problems, so It's hard to say which is causing the issue.

Thanks

Edited 9 April, 201313 yr by prankstar2003

Sounds like trapped solvents to me when did you spray your primer

Edited 9 April, 201313 yr by doyler

when you lightly pull the trigger air will come out of the gun but no paint- this flow should be 30/40psi based on what is the manufacturers recommendation for a 1.4 nozzle on that gun - i always paint an old panel first to ensure the paint sprays right first and adjust the pressure to suit. you will want more pressure if the paint is thick and less pressure if its thin. its all about the feel and how it sprays- get an old panel to set it up on first.

how are you thinning the paint down? are you using 2K thinners? or standard thinners?

what distance are you holding the gun at from the panel.

and last off - was the panel hot when you sprayed it?

Right, thanks for that kiz, I'll check those pressures. The panel wasn't hot no. Spraying around 6-8" from the job with 2k thinners (as per instrictions). From what I've read since posting, it's likely a pressure issue.

Regarding feel, although I initially had issues with paint being too think, I thought I'd gotten the technique when doing the primer.

Doyler: primer was done 3 days ago, and it's been stored in the warm since. So I doubt it's trapped from that

when you say stored in the warm - what do you mean?

you would tell if the primer was not right when you wet flatted it- did you panel wipe it after that or use thinners to clean off the wet flatted paint?

Just room temperature, nothing too warm. I use panel wipe whilst prepping

You can still get trapped solvents in the primer as in if you didn't let it flash off properly before you apply anther coat which then will effect the top coat

Edited 9 April, 201313 yr by doyler

right, I see. Wouldn't that have bubbled the primer though?

right, I see. Wouldn't that have bubbled the primer though?

No it would of only become apparent when you apply the top because your adding more solvent and the trapped solvent can't breathe

Ok, what do you suggest?

Ok, what do you suggest?

It all depends on the extent of the solvent pop the remedy is similar to microblisters in worse case strip it right back bare and start and again and if its not that bad flatten it seal it and reply the topcoat

seal it? how would i do that? I think i should get away with rubbing it back

seal it? how would i do that? I think i should get away with rubbing it back

Base coat sealer or thin your 2k primer out so it has the conisentcey of a wet and wet primer

not much more i can add to that. id wait a while and flat it back - wouldnt go as far as going back to bare- as once its gone off and you have flatted it back you should be fine

Pin eyes from what i know can be from sylicone in the paint/atmoshere irrc ..

Dont know if its the problem your having but sylicone is a no no in bodyshops etc .

Spot on. Silicone molecules every time!

If you have ever sprayed an aerosol lubricant or anti-seize in the viscinity that will be the cause.

You can get an additive to counter this but it's very expensive.

My mate used to flat back 'soapy' using 1000 grit in warm water and rubbed on a bar of fairy kitchen soap then washed off with cold water, air dried then spray again ASAP. That seemed to work.

I prefer cellulose and use the bar of soap method with that and never get any sort of contamination.

what kind of hose are you using si? some cheaper air lines can have trace amounts of silicone in them, which can cause issues with paint contamination. also what kind of compressor are you using? does it have a good oil and water trap on it?

Yeah, oil and water trap are there. And surely the silicon contamination would have been present in the primer layer too? It's on several panels as well, one being brand new (so no chance of silicon exposure). I did the second panel to rule this, and other contamination out. I'm pretty sure it is due to attempting to put on too much paint at once at too higher pressure.

How long to wait until I flat back then? I'm not touching it today, Thursday be ok, or longer?

it wont be that as you would have got it in the primer- I'm fairly sure this is due to how the paint was applied.

how did you spray it- step by step including times between ect ect.

Trapped solvents are not just a case of paint being put on to think or 2 much thinner there's a vast number of reason

Solvent or air trapped in film escapes during drying leaving pop marks.

Incorrect spray viscosity, spray pressure, flash off time, or improper drying.

Incorrect choice of hardeners and/or thinners. Use of fast-dry thinner or reducer, especially when the material is sprayed too dry or at excessive pressure.

Excessive film thickness. Insufficient drying time between coats and too heavy application of the undercoats may trap solvents causing popping of the color coat as they later escape.

Incorrect drying of primer / fillers.

Improper surface cleaning or preparation.

Infrared facilities too close.

Baking was started too soon after application.

Baking temperature too high

It's sounds like trapped solvents to me as your an inexperienced painter your spray pattern/method may need practice you need to think as your self as a robot when painting you need get in a habbit of being uniform and learn how to adjust you gun accordingly Etc it just takes practice watch a few videos on YouTube watch the way the move the gun and there technique

Hope this helps

Edited 10 April, 201313 yr by doyler

thats what i was getting at doyler- its going to be one of these reasons- to much paint for the flash off times, no dust coat, high air pressure etc etc - spraying at home isnt easy at all as theres a lot more factors to consider compared to a bodyshop. i can imagine that without proper extraction the solvens were in the air around him and that has an impact on the solvents evaporating.

oh and dont have a fag in there

Thanks for the advice. The bubbles came up practically instantly if that helps narrow this down. I did a guide coat however, but the paint went on as one coat, as in the finish was so 'good' and thick it didn't LOOK like it would need another, saying to me it's too thick.

I'm overlapping fans 50% to get an even coverage but I have found a few saga/runs which again is an indication of too much paint correct?

What's the recommended time to leave between coats then?

Again, thanks for all the advice. With an old suction type gun I got reasonable results, so I think my technique is ok, I just need to get used to this hvlp system. It's a pleasure to work with ib that it lays the material on uniformly and overspray is minimal, just a few creases to iron out

sounds to me like you are whacking it on! solvents trapped by how thick the paint is on the panel.

Suction guns and hvlp are completely different in the way the spray etc just a heads up

I'm beginning to see that