Troubleshooting Micro Bubbles in Pigmented Conversion Varnish

Sometimes the simplest quick answer is to switch brands. May 16, 2014

We have been using ML Campbell for years without issue. For the past 3 months, we have had issues with pigmented topcoats, and they are really bad right now. Micro-bubbles are popping up after having a mirror finish when wet. We were using Resistant and switched to Stealth to see if it would help. The major bubbles are gone but now the entire surface has smaller bubbles throughout, creating a finish that feels smooth but looks like crap when held up to light after it sets up. I don't care what the problem is, I am not looking to point fingers. I just need it fixed. We have 0 issues with Claw-lock primer and clear coats. It is just the pigmented topcoats. I am at my wits end! Help! I thought it was a humidity issue since it has been really bad, but the weather broke and it is still a problem.

Same problem in both gravity feed and Graco and Kremlin pump guns. Same problem whether we put no solvent in it or a combo of solvents from nothing to 25%. Standard thinner, Care thinner, Care reducer, flow enhancer, it just doesn't matter. The problem just morphs to a different type of crap finish solvent pop/bubble issue.

Forum Responses
(Finishing Forum)
From contributor M:
I would try lowering the air pressure. A lot of times too much air is the cause for air bubbles in solvent based finishes. If that doesn't work, I would try a different product.

From contributor S:
- Humidity/ temperature/ barometric changes noted - do you have intake filtration?
- Are your delivery system(s) dedicated to pigment?
- Does the issue occur on vertical surfaces as well as horizontal; i.e. mil thickness/air flow velocity?
- Have you removed freshly coated product away from air flow and allowed to flash?

- How much time has elapsed between your standard mil thickness primer coating and scuff; and then pigment coating; might static electricity be an issue?
- As a test, have you tried a mist coat of pigment, allowed a quick flash, scuff/tack followed with a standard coating?
- Have you primer scuffed, done your standard dust removal - air blow off/tack, reprimed and done a light check?
- Have you revisited pigment jobs and done your visual light check?
- Have you done the light check with your clear coatings; checked with a magnifier?
- Have you consulted with a truly knowledgeable tech rep/lab person or sent off a sample - better yet, step sample to the lab?
- Have you created a potential cause list - including the most outlandish possibilities and then checked them off?

From contributor F:
I had the same problem with Resistant and then with Stealth. Identical to yours, in that they worked perfectly for years, then I started getting tiny bubbles. I was told to reduce by 10% with Care reducer. That didn't work and I had a deadline. So I quickly switched to Matador by Becker, which I had used off and on for a few years. As far as the MLC problem, I could never figure it out. If you have a crunching deadline, with all you already tried, I would just make a switch and get the job out the door.

From the original questioner:
We thought it was the humidity because it was very high. But the temp and humidity just dropped down to optimal levels and are still an issue. We have a heated and filtered air make up system. The heat is off just on fan mode.

Yes, dedicated gravity feed and AAA for pigments.

Yes, we've tried on vertical and horizontal surfaces. Have tried all combos of flash times and builds, all it does is alter the issues.

Some have stayed in the booth and other parts have been moved out to drying area (still air flow). Resistant we had very large bubbles and less of them that came to the surface almost immediately after coating, from seconds to no more than 1-2 minutes. Stealth lays out like glass at first, then as it dries over an hour, there are way more very small bubbles. It creates a pretty consistent visual texture throughout the entire surface.

All parts whether scuffed in advance or not are hit again right before coating.

Yes, we've tried a mist coat of pigment, allowed a quick flash, scuff/tack followed with a standard coating.

Yes, we've done both air blow off and tack wipe. We've reprimed and done a light check . No issues whatsoever with primer.

We've had no issues before approximately 3 months ago. We have no issues with clears.

We had a rep come to our shop to help. They recommended the switch to Stealth, offered no explanation of Resistant issues. Did not send to lab. We have cleaned and serviced everything used in the process.

I am thinking we should try one more thing, and that is to get the parts out of the booth ASAP, which we have not been doing with the Stealth. At this point we have lost thousands in labor and are just simply out of time - job is now overdue. We need it all out the door this coming week, no if, ands or buts about it.

From the original questioner:
Going to do another test, thought about this after typing the last response. Maybe left the Stealth in booth too long before moving. Going to shoot two samples side by side and move one immediately out of direct air flow. I am thinking because of it occurring so long after the fact that it may be we left in direct airflow too long before moving and the surface was flashing off before the solvents underneath had time to. We have two 14 booths side by side with huge airflow. Fingers crossed.

From contributor B:
Probably not the cause, but when something that worked fine becomes problematic no matter what you try, this is the point in troubleshooting where I start tearing my guns apart to check for problems, before a thorough cleaning. Also a good time to check lines, pots, regulators, and air supply, etc. I am sure you have probably done this.

From the original questioner:
We did do all the cleaning. We tried the direct air flow and out of direct airflow. No difference at all, none. So we are going to jump ship. Now that everything is primed with Claw-lock, do you think there will be compatibility issues with the Becker Acroma topcoat? I would rather not have to re-prime from a labor perspective and also total film build issues. But even more important I don't want any adhesion issues, so if we have to sand and re-prime, so be it.

From contributor W:
Same thing happened to me, 3 days ago. The only thing I have done different from in the past is started using their new cleaning thinner. Never had trouble before that and I tried all the things you did to remedy it and did not succeed.

From contributor F:
Sometimes you just have to bite the bullet, and get the damn thing done. You will not have any adhesion issues by using Clawlock under Matador - I used it for many years. Then I switched to Becker. But both work well.

From contributor J:
Clawlock is a fantastic product, probably the best MLC makes. You will not have any issues putting pretty much anything over the Clawlock.

From the original questioner:
Thank you all for helping me with a plan to get this job out the door. I would still like to diagnose it to see if it is something we are doing wrong, so we can fix it. After so many years and samples made I don't want to switch over the entire line if we don't have to. Contributor W, what is the solvent you used? We have 4 different solvents from them - standard thinner, flow enhancer, care reducer and care retarder.

From contributor W:
it is a 5 gallon can of fast cleaning thinner. None of the thinners you mentioned have affected my finishes until I started using this cleaning thinner 2 weeks ago. The cleaning thinner is half the price of k-120 and only used for cleaning.

From contributor S:
May I suggest that you have more reducers than you need? Standard (which can be used as a cleaning solvent, unless you use the air/solvent cleaner system, in which case use acetone) and flow enhancer should do it.

Perhaps air flow is more than excessive - if you can control it, a slightly positive air flow should be all you need, and then if combined with improper solvent or solvent ratio, results can be rejected.

Try 2 samples using just flow enhancer 5%-10% added. Coat right before lunch, one sample vertical, one flat. Turn booths/air intake off. No air flow! If air flow cannot be immediately/fully restricted, then cover samples with a cardboard box upon hanging up the gun! Sounds silly, no? Enjoy your lunch and have a laugh or two.

Send a step sample to lab. Write on the back species of wood, raw wood sanding process, plant conditions, primer used, system used, elapsed coating to scuff period, etc. Document as thoroughly as possible.

From the original questioner:
Just sprayed the first batch of Matador for the past 5 hours. It looks like a million dollars, no issues at all. Seriously, the absolute best pigmented finish we have ever put out. No other changes; same spray equipment and maintenance, same booth and intake air, same sprayer. Much higher solids and went a lot farther per square foot too.

From the original questioner:
I listed off all the thinners we have - they are not all used together. The standard thinner we use for cleaning and reducing Krystal and vinyl sealer and the Clawlock. The flow enhancer we were using on Krystal topcoat and the Resistant. We tried the retarder when we started to have the issues to make it stay wet longer, hoping the bubbles would dissipate and the finish would flow back together. The Care reducer was added to the mix when we started with the Stealth because that is what they recommended.

We did tests from 0% reducing all the way up to 25% in both Resistant and Stealth with pretty much every combo you can think of with the same or similar results. This Matador we mixed exactly what they said; 12% catalyst and 20% of their 219 reducer. It sprayed perfect.

From contributor M:
Glad to see you found a solution - stick with the new finish. You should not have to go through that much trial and error to try to get a CV to perform well. Any good CV should spray good without having to keep track of humidity, barometric pressure, rotation of the earth spinning, making sure the stars are aligned properly. The most I ever do is add a little retarder on very hot days in the summer. Other than that, I do nothing but spray. It comes out like glass every time.

From contributor V:
The last time I had a similar problem with a different CV product, I did a ton of testing and replaced lines, driers, guns, etc. The problem was a bad batch of finish, plain and simple. It was finally diagnosed by mixing up a fresh batch of finish and pouring it out on a smooth sealed surface. Glass was recommended, but I used a piece of melamine that was carefully cleaned before the test. Almost immediately, micro bubbles appeared all over the test samples (I did more than one). After that batch of CV, I've never had the problem again. About a year later I switched finish manufacturers for other reasons.

From contributor Y:
I switched from MLC CV products for this exact reason, and a host of other little ones. Here in the hot and humid south, some days, it was almost impossible to stop what you are dealing with. MLC is not a bad product per se, but it is manufactured and tested in Canada. They just don't get what it is like here, and I spray in a booth, but not a laboratory. We also used 5% BC Super retarder (MLC) as part of our chemical cocktail. If you insist on staying with MLC I can copy off some of the pages of our spray log that shows the different preparations we had to do to get MLC to spray right in different conditions, or let you talk to my finisher who figured all that out.

If you can get Becker CV, and good support, mixing, etc., it is the bomb! Same ratios every day, hot, cold, raining, desert. It just worked perfect, without having to have a chemistry degree.

My Becker distributor sold out here, and trying to get Becker and support is difficult, so I chose to go with SW instead. Some will argue that SW owns Becker (true, but only fairly recently) and they have adopted their chemistry. I beg to differ, a lot. Having sprayed them both, Becker is still better than SW, but the SW is far less finicky than the MLC. I will not spray MLC again, and I did so for about 12 years.

From contributor N:
I am currently spraying Stealth for all pigmented jobs but have been very interested in giving Matador a try. Looking at the product sheets, is the dry to sand time really 2-4 hours? Seems a good bit more than Stealth. Anyone had issues with this?