Troubleshooting Dry Particle Problems with Conversion Varnish

Small whitish particles in CV straight from the can could be flatting agent, a temperature issue, or something else. Here are some tips on identifying and solving the problem. July 3, 2008

Previous to the last few years, I used MLC Krystal satin without any problems. But during the last few winters, my conversion varnish has appeared to have small particles of dried CV in it when spraying. If I open a new bucket of Krystal, similar particles appear to be floating on the surface. I cannot seem to filter these particles out. I have tried flow enhancer, standard lacquer thinner, and reducer. My usual spray environment is about 72-75 degrees at 25-60% humidity here in West Virginia. I have tried both compressed air and turbine air sources with HVLP and also compressed air for HPLV. Nothing seems to make any difference. When spring comes around, this problem disappears. Has my conversion varnish gotten too cold during shipment? Anyone else having similar problems? No MLC reps have been able to help. If I haven't given enough data, please ask away, as this problem has probably cost me $20,000 the last 2-3 years in lost production.

Forum Responses
(Finishing Forum)
From contributor C:
Are you using a paint tank/pot with hoses or strictly cup guns? Either way, do you disassemble the cup gun and clean it thoroughly (brush cleaning, etc.), or just run solvent through it? Again, if it's a paint pot with hoses, have you left the material in there overnight or longer? When not used, do you flush out the material hose with plenty of thinner and leave it in the hose until next use, then flush it well again? Though it may be a problem with a cold sensitive additive crystallizing, it also may just be that the equipment needs a real good cleaning. I usually change my hoses out every couple of years, which avoids these problems if they're due to buildup in the lines or guns. If you're positive it's only happening in the winter/cold months, though, it could well be a problem with additives.

From contributor C:
Have I misunderstood - are you saying that the material is arriving in that condition? It's that way when you open the can? Are the particles hard/crunchy, or do they smash up easily when compressed between the fingers? Have you tried to dissolve some again with the appropriate varnish thinner? Any coating that cost me 20,000 I would abandon in a heartbeat, and would find an alternative if the problem was not solved in a short time by the coatings company.

From contributor W:
Get a piece of glass, make sure it's clean, and then pour some of the finish on it straight from the newly opened container. Let it dry and see if you can see the same problem on the glass as your wood. If it's on the glass I would be yelling a hole in someone's ear after 2-3 winters with this problem and no help from the reps. If it's not on the glass, start looking for dirty or cheap grade thinner causing the problem. About 3 years ago I had the same problem two times with Magnamax. One time was a bad batch, and the other was bad thinner.

From contributor T:
Is it possible that you have a coatings product that has expired? Most have a manufacturing date on the can. I wouldn't use anything that's over the date on the can by 4-6 months. Most times it's the flattening agent in the can that goes sour. Ask your girlfriend for one of her nylon stockings and make yourself an inline filter for your pressure pot or spray gun. That nylon mesh is real fine and if you fold it in a few different folds, not much of anything except liquid can get through. Use a clear lock tie on the spout and you're good to go.

From contributor R:
There could be a couple of reasons for this problem, but since you mentioned that it goes away in the springtime, I tend to think that it is temperature related. The product could be cold from shipping or simply sitting on a concrete floor. If your flammable cabinet is located on an outside wall, it could also be several degrees colder than your shop. Pour a small amount, including the little particles, into a container and bring it into some place warm for a couple of hours. To speed things up you could set the little container in some warm water. Sorry, but I have to say this... do not use any exposed flame or heating device to warm the can or the container of water while the flammable finish is in it. I don't mean to insult anyone’s intelligence, but we all can get a little overenthusiastic at times. My guess is that when the finish warms up, with a little stirring, the particles will easily melt back into the liquid. If this is the case, you should start looking for the thermal bandit.

From contributor I:
If it's crusty when you open the can, insist on a new can from another batch.

From contributor R:
With this particular product, if it's cold, it most likely will be crusty.

From contributor I:
Never had the crusties here.

From the original questioner:
Thanks for all the responses. I have tried pressure pots and siphon feed. I replaced guns, both air and fluid hoses, double filtered, and everything else I could think of, some of which didn't make sense but I tried them anyway. I flush my lines and cups. I wipe the cups and then fill the cups with thinner, and leave thinner in the hoses when using hoses. I never leave finish material in hoses or cups overnight.

And yes, my material comes that way straight from my distributor. The particles are not hard in the can, but when sprayed and dry, they do feel rather hard. I have not tried to dissolve the particles with thinner.

I have put the material on glass and the same particles appear and I never use cheap grade thinner or dirty thinner.

About 2 weeks ago this problem surfaced again. Since this hadn't happened until about March 1st, I thought perhaps the material had been corrected since I had heard all the manufacturers had changed solvents a couple-three years ago. I met with a MLC rep and he told me the material that started the problem on March 1 had been manufactured in Nov 07, only about 4 months. He seemed to think the flattening paste was not dissolving properly. He said my distributor should shake the material more thoroughly to see if that would help. Thanks for the nylon hose tip.

I will see if warming the material will allow the particles to melt back into the liquid. I didn't understand what was meant by "start looking for the thermal bandit". Can you explain?

The material is not crusty, but I can see very small particles floating on top of and in the material.

From contributor C:
If the particles are not turning white, then I doubt it's flatting agent.

Form the original questioner:
When looking at the dried particle under the MLC rep's microscope, it appeared to be a white flake-like particle.

From contributor C:
Spray it on something black to make sure, but if it looks like a white particle under magnification, it sure could be flatting agent. If you use the method to strain, gather all the contaminant and let it dry out on something dark and see if it turns white. The thermal thing contributor R was talking of was an additive that would cause this to happen by thermal properties of the unknown problem component.

From the original questioner:
The pantyhose filter seemed to help immensely. I went into the shop Saturday between appointments and put two coats of Krystal on two different sheets of plywood and they did great (and this was using the same can of material that caused the problem). I'll make a few more tests to see if the problem is for sure gone. If the in-line panty hose filter continues to eliminate the problem, then you will have filled a prescription for me that is the equivalent of Viagra.

From contributor T:
I learned that quite a few years ago and have used it ever since on both the spray guns and pots. Sometimes that flattening paste can be a real bugger to get fully mixed into the coating.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
If conversion varnish is not at room temperature before mixing it and you get it ready to spray it will give you problems, especially in winter. Keep all containers in a warm room.