Biggest cause of solvent popping?

[Scott Gardner]

I'm trying to figure out what the causes are for solvent popping (those little bumps you get in clearcoat that become pinholes after you've wet-sanded and buffed it).</cr>
On my first couple of jobs, I thought it was inadequate flash time between clearcoats. Later, I found that I could get them even with just a single coat of clear, if I put the clear on too heavy. The maddening thing was that I would try to be consistant from one part to the next, and some would get pops, while others wouldn't. Also, it seems like the pops only occur on the horizontal surfaces of the parts.</cr>
The last two jobs have been pop-free, though. On one of the two, I over-reduced the clear by about 50%. On the next, I used the recommended amount of reducer, but used the next higher temperature range reducer. (It was 75F in my booth, and I used the recommended reducer for 80F-95F.)</cr>
On the tank where I over-reduced the clear, in addition to not getting pops, the clear seemed to flow out a lot flatter than when I used the recommended amount and went with a hotter-temperature reducer.</cr>
So the question for the experts is, should I always over-reduce the clearcoat and just be extra careful not to get runs? How about the reducer itself? Should I get in the habit of using one temperature range higher than recommended? How about over-reducing AND using a warmer reducer? Newbie minds want to know.</cr>
Thanks a bunch,</cr>
Scott

 

[TAZ]

Scott,
Solvent pop is caused when too much paint is applied or coats are applied on top of each other too quickly. When this is done, gases from the reducer from the lower portion of the clear, are trying to escape, but they are trapped because of the paint thickness or the coat that was applied on top of it, thus creating the bubbles known as solvent pop. This is why you have a tendency to get the solvent pop on the top surfaces easier (or on cars/trucks on the edge of the jams), because clear is usually applied heavier on the tops surfaces. Applying too much material could also be caused by an improper set-up on your gun. Check what the paint manufacturer recommends and what you have on your gun. This could be another culprit for solvent pop.

Reducer does nothing more than to help the clear flow. Since you are making the clear thinner, it goes hand-in-hand that your clear is laying on flatter. Keep in mind, at the same time, your are not putting on a "true" coat of clear since quite a bit of it is reducer (so be sure and add a couple more coats to compensate for this). I would suggest using the correct reducer or one grade hotter if you can work with it. With the PPG 894 (not 893) mentioned below, it is virtually impossible to use medium while doing a tank set even though my booth temp is currently 100. I still use fast with the 894, but have to use slow with the 893 (and it still will pop easily).

What clear or paint line are you using-PPG?
I have found that PPG 893 is the most sensitive clear to solvent popping.
I consider this clear to be very un-painter friendly. If you use the PPG894 clear, this will not solvent pop, but stays wet forever and you have to pace yourself with this clear.

If you are using a polyurethane basecoat system, you might want to try the House of Kolors clear. It is *very* painter friendly. Very hard to run. I have never seen solvent pop with this clear. It also dries very quickly. I can pull the parts out of the booth within an hour and a half after painting (keep in mind, it is 100 in the booth) This is they type of clear, you go with the proper reducer. I use slow with the "exempt" hardener (uk-150). It is a little hard to buff though.

 

[rex]

Like Scott said check your gun setup.When PPG came out with the higher solids Concept clears I didn't change my gun,a DeVilbiss MBC.I could get a nice job but I was on the verge of popping,so once in a while I'd misjudge the reducer and get a little pop.If you decide to over reduce find out what the manufacturer recomends if they do.You have to remember the more reducer you use the more risk you run of the clear dying back later on and buffing again won't always cure it.I think your best option is go with a slower reducer to keep the top open longer.You can also blend the reducers together.If you do stay in the natural progression though for best results,like blending medium with slow,not fast and slow to make medium-that screws up one of the drying stages usually.Reducers have staged drying and slow and fast are made up differently chemically.Usually there's 3 drying stages to a reducer-a carrier solvent that evaporates in the air before the paint hits the part(this can be forced into the if you spray too close and can cause problems),a solvent that controls the initial flashing and a solvent that controls thru drying.Mixing fast and slow together screws one or more of these properties up.What gun and brand of material are you using?

 

[Verwokkfrpew]

Very good and informative exchange .. Thank you!