Solvent Pop

[Model1VH2]

Hey guys,
I need some help preventing solvent pop in my clearcoat.
I have no idea what I could be doing wrong ...
I'm using Dupont Chromaclear with a high temp activator in order to slow the curing process in order to prevent solvent pop. I'm waiting 30 minutes between coats, which should be more than enough time for flash, and I spray in a climate controled environment with low humidity and I run a water/oil separator at the gun and drain any condensation from my tank before each use.

I've read some hot rod forums where they are using the same stuff and someone suggested shooting the clearcoat without the activator.

Have you guys heard of this?
Will the clear cure properly (just maybe take longer?) and still be as durable?

[DrDoug]

I am only experienced with Sherwin-Williams Ultra 7000 paint systems, but it is a 2K (two component) system too. Solvent pop is related to the speed that the top of the finish forms its surface/cross links. Once this happens, any solvent under it will be trapped. What you need is to use a retarder and a slow reducer, and stick with the hardner (2K system). If you do not use a hardner, it will never harden fully.

Mixing the clear is a balancing act based on humidity and temperature. Higher temps mean a slower reducer, and vice versa for lower temps. Also, you do not want to overdo the hardner as this can also lead to solvent pop by skinning too fast. Measure carefully! Use of a retarder will keep the surface from forming its cross linking too fast, allowing the solvent to fully evaporate.

The best thing to do is to use the right reducer, and then let each coat stand about 3/4ths of the max recommended between each coat. This will allow the maximum solvent escape before applying the next coat. Also, do not apply too much for each coat, this can cause solvent pop too!

When I shoot the color, I let it stand the maximum time before I apply the clear system. I get perfect results this way, and it gives me more beer time between coats...lol

What reducer were you using, and how hot was it when you were applying the clear?

[Model1VH2]

Thanks DrDoug.

Sounds like I'm doing all the right things ...
I wait at least a day after spraying basecoat before spraying clear.
I wait about 30 minutes to allow for proper flash.
I use a high temp reducer which has a retarder in it.
I spray in low humidity, climate control conditions.

To the best of my knowledge, I'm doing everything that is recommended and taking precautions to prevent everything I've been told to avoid.
Still, I'm having these problems.

I don't get it.

[Newc]

Maybe it's reacting to the paint under the clear?

[Model1VH2]

Maybe it's reacting to the paint under the clear?

Same Dupont acrylic urethane underneath.
Nothing different.

You guys have no idea how frustrating this is.

[mm2002]

Are you sure it's actually solvent pop? Can you post a picture? It definitely sounds like you're doing all the right things, even some a little over-kill (flash time). I had a solvent pop problem one time, and it was simply because I was an idiot and grabbed the wrong can of hardener (fast, in hot weather). Otherwise, I shoot base and clear the same day, and all within about a 2 hour window.
If it IS solvent pop, and the problem persists try this: Mix your clear and hardener, then reduce that 10% with slow urethane reducer. You won't get as much build this way, so it will take an extra coat or two, but the solvent popping should not happen. Also, make sure you're not spraying it on too wet. Are you getting any runs?

[69dodgecharger]

this is stupid, but how wide of a fan are you using when you spray, and what is your air pressure at? Maybe your are just trying to lay on too much clear, that will give you solvent pops, and other issues as well.

[Model1VH2]

Are you sure it's actually solvent pop? Can you post a picture? It definitely sounds like you're doing all the right things, even some a little over-kill (flash time). I had a solvent pop problem one time, and it was simply because I was an idiot and grabbed the wrong can of hardener (fast, in hot weather). Otherwise, I shoot base and clear the same day, and all within about a 2 hour window.
If it IS solvent pop, and the problem persists try this: Mix your clear and hardener, then reduce that 10% with slow urethane reducer. You won't get as much build this way, so it will take an extra coat or two, but the solvent popping should not happen. Also, make sure you're not spraying it on too wet. Are you getting any runs?

Sorry, no pics.
When you say " reduce with 10% slow urethane reducer", do you mean a retarder?
I actually considered doing this, but I figured if I couldn't get decent results with a high temp activator than I should probably look at something else I may be doing wrong.

I do have a helluva time trying to get a nice even spray with my gun.
I seem to get more "spitting" than I do shooting my basecoats which almost always come out damn near perfect!
The clearcoat is alot thicker in viscosity than the basecoat and it's been really hard trying to dial in a good setting on my gun.
It either comes out dry or it spits ... no happy medium.

I'm using about a 5" wide fan and running it between 35-40 psi at the gun with a 1.4 nozzel.
I drain my tank of any condensation before each session and I use a water/oil separator.

Maybe it's just time for some new guns.

[mm2002]

Well, you just answered your own question! You say the clear "seems" thick, and you are using a 1.4 tip. The reason it seems "thick" is that the gun isn't atomizing it properly. The result of that is you are laying it on too heavy attempting to get a smooth gloss (causing the solvent pop). Use the reducer (not retarder) to thin the viscosity of the clear, crank down your fluid volume a tad, and it will spray just like the base color. No more solvent popping! Try it, you'll like it!

[DrDoug]

I agree with mm2002, you answered your own question. If there is 'spitting' going on, your mix is too thick and it needs to be thinned (reduced) to atomize properly. Upping the pressure will not do the trick, you need to have a proper viscosity and pressure combination to spray clear so that it lays down thin and smoothly.

The 1.4 nozzle, a thick viscosity mix and high pressure are the problems. You probably would have less spitting using a 1.6 nozzle, but you would be laying down too much clear with each coat.

Keep the 1.4 nozzle, reduce your clear and drop the pressure and you should see immediate results. If you are using an HVLP gun, you should not have any more than 24-28 psi at the hose/gun junction (to compensate for line pressure drop when spraying). I run mine at 22 to 24 psi for clearcoats. I crank my compressor up and use a cheater valve at the gun to control pressure. It works great and I can make pressure adjustments on the fly.

Good luck! Once you get the combo figured out, you will never forget it! I enjoy special projects like this, and I am planning on doing the same to one of my guitars soon. Nothing cooler than being able to do your own custom paint work!

[Model1VH2]

Thanks so much guys.
You've all been a great help.