Trouble with a Translucent White Finish

      White flecks are separating out of a heavily thinned white pigment finish. Finishers try to troubleshoot. May 17, 2005

Question
I am trying to spray a very translucent white. My formula is as follows:
1000ml of Nitrocellulose Dope (manufacturer recommends thinning by at least 1:1)
2000ml of manufacturer's thinner
150ml of manufacturer's universal retarder
50ml of white pigment

When I spray this, it leaves a transparent build, but dries clearer and with small white specks. From 3' it is not noticeable, but at 1' it becomes apparent. It was cold (high 40's) last night when I sprayed. The lacquer was mixed for every batch shot out of a gravity gun. The lacquer did seem like it would not atomize well. More air just made it go on dry. What should I do differently?

Forum Responses
(Finishing Forum)
From contributor W:
It could be that the pigment was over thinned. If a mixture with a pigment gets too thin, it will run out when it no longer can bind together. Some dyes and stains do the same thing when they are thinned too much. You might try a fast drying pickling stain (PPG/Monarch makes a nice one). And then shoot a water white clear over it so it won't yellow.



From contributor J:
You say you didn't want it to settle out? Or is it what you expected without the white specks being left in suspension? If the mix was doing all that you wanted except for these white things left behind, I would guess that A). The titanium being used is not compatible in the solvent used and is falling out. B) The use of the retarder in combination with cold temps is allowing settling to occur and needs a hotter, faster thinner or to leave out the retarder.


From the original questioner:
I thought that I might have thinned too much. What does run out look like? I want a very transparent white, uniform, not speckled. It could have been that the retarder and temps allowed this to settle (or clump?). Or the pigment was not compatible. How can I verify this? Could I take more mixture, not as thin, and add less pigment? Say, cut the pigment and the thinner by 50%? If they are not compatible, then I will still get clumping, right? If it does, how much could I thin a white lacquer primer without it beginning to separate? I think the pickling stain may be too opaque. Can I thin this without effecting the dry time? Also, could I use a conventional gun to get better atomization? I don't think that my airless will give me the control that I want.


From contributor R:
What type of universal tinting color did you use? If you used a product designed for water based paint (like CalTint), it will not stay in suspension properly and you will get speckles.


From contributor J:
Why did the manufacturer sell you retarder or did you ask for it? Buy the cup strainers that they sell at automotive paint stores and double up about two of the finest mesh ones you can get. Mix the white up with the thinner in a separate can and stir it up well. Pour this into the strainer into your pot or gun, then add the dope in and mix gently so you're not getting too many bubbles mixed in. Let this sit for 10 minutes or so to settle down a little. I'm also curious if you're seeing the white specks correctly and assuming it's pigment flake instead of tiny bubbles that didn't break the surface for release.


From Paul Snyder, forum technical advisor:
Sounds like you either have insufficient atomization or the pigments aren't a good choice. I'd use some quality micro-ground pigments (that are compatible with lacquer) and make sure the spray gun is atomizing very well.


From the original questioner:
I'll probably be going in a little later today. I'll check the pigment. It was something he supplied, packaged for guitar use.


From the original questioner:
How about this: using ICA white dye in this mixture instead of a UTC. Supposed to be smaller particles, but alcohol based? Is this right?


From contributor D:
You are adding 5% colorant to your lacquer. That should be okay. The threshold is usually 6.25% (2 oz. per qt).

First things first. Add the colorant to your reducer (let it down in your reducer). Then, after that is thoroughly mixed in, add that to your lacquer. After all, you are going to reduce that with this amount anyway - might as well make the reducer colored. The color will mix better with the lacquer and you already have enough binder per colorant regardless of how much you reduce. The binder to colorant ratio remains the same.

Next, you must strain your mix through a fine mesh filter. Then you must make sure that your gun is really clean. Clogged air holes and fluid passages are no help to anyone, let alone you.

If you are getting speckling after all that, then you have incorrect settings on your gun. Do you have enough CFM to power your gun? Is your needle/nozzle set the right size for the viscosity and rate of fluid flow for the material you are spraying? Have you dialed in the right amount of fluid to deliver to your gun using the fluid control knob on the gun? Is your colorant compatible with your lacquer and solvents? I am assuming that the problem has to do with the gun settings. Mixing the colorant in the reducer is something that will also help.



From Paul Snyder, forum technical advisor:
There's no such thing as a white dye. It's really a micro-ground white pigment that's ground so fine it behaves like a dye. ICA and ILVA are a couple suppliers. Just make sure you get one that's compatible with lacquer thinner/acetone. If it is, it should work well with good atomization.


From contributor W:
You can use the Monarch/PPG fast drying pickling as a spray if you thin it with regular lacquer thinner. I think you can get the effect that you are looking for.


From the original questioner:
Thanks, I am aware that there is no white dye. That's what my supplier calls it.

I mixed up a new batch this afternoon and shot it with 2 different guns, an import gravity gun and an Accuspray 19 cup. The gravity gun was either hit or miss. It will either not atomize or will flash it. The Accuspray does a good job of laying it down. I want to see how it does when it is dry. Last time I sprayed, it looked good until it dried, then speckled. I will probably try the ICA white tomorrow with a new batch.

I may give that pickling a try, too. How is Monarch's tech support? I would like to know how much I can thin this.



From contributor J:
You know what we used to use for white washes and glazing bases or colorant when we didn't have any of the standard ingredients? Enamel paint. After all, what is a thinned stain whose base is M.S.? It's enamel (minus a binder, but that still is a Minwax type base). Go to the paint store and get the white base colorant and if you want it whiter than its present shade, drop in a teeny weeny bit o' blue.


From the original questioner:
Could this blotchiness be caused by too big of a setup (needle/air cap)? If I set the fluid on the low side, it mists, and if I set the fluid higher, it clumps as it dries - goes on wet and smooth. I have sprayed with 3 HVLP guns, an import gravity gun, Accuspray cup gun, and a Graco Delta with a pressurized cup. Would a conventional gun do better in this situation, or should I move more to an automotive gun?

I tried the Monarch Fast-Dry Pickle, and cut it by 50%. Works the best so far. But still clumpy/blotchy. If I increased the lacquer, would I get better results?



From contributor B:
What the heck are you talking about? Reread your last post and see if that makes any sense to you or not. You wouldn't be having problems with your coating if you had taken one of the bits of advise from any one of us. I say strip it and do it like it has traditionally been done and not with the modeling dope you're using.


From the original questioner:
This is what I have done so far. I mixed 2 different pigments with dope, one labeled as a guitar finishing pigment, the other ICA microfine pigment. Then I ditched the dope and mixed pigment with Valspar precat; I thinned Valspar white lacquer primer, and I shot Monarch Pickling (lacquer based). The only thing I haven't tried is to thin enamel.

The problem that I am having is that to get the transparency he is looking for, the material seems to dry splotchy. It is not a uniform coating. After spraying all of these products, I am still getting uneven coverage when it dries. I am at the point now that it is either my equipment or my technique, or some other variable with the product (i.e.- temperature).

My questions are:
1) Would a conventional gun be a better choice to apply this type of material?
2) Would I benefit from a gun that shoots a Class A finish? (My guns are set up for thicker wood finishes, i.e. conversion varnish.)
3) Would I do better to cut back on the pigment and use my regular guns?

This seems like it should be simple, but it's just not working. Is it equipment, technique, or product?



From contributor B:
Straighten me out here because I still am not sure if you're looking for a painted white that has depth to it or a stain, fairly white but still showing the wood beneath it.


From Paul Snyder, forum technical advisor:
I often use a white toner over a white pickled finish to brighten the color and even out minor variations. Sounds like you're trying to do the same thing without using a pickling stain first.

Very good atomization and very thin application (coats) along with good spray technique are key to getting good results. If you spray it too wet - meaning either too heavy a coat or the fluid flow is too high - you will get pigment clumping.

Use a small needle/nozzle appropriate for the low viscosity of the toner and enough air to atomize it well (just short of fogging). Back the gun away from the surface an extra inch or two to get into the finer/misty zone of the spray pattern. Lay down an even wet coat and overlap enough to avoid stripes. The coat should be thin enough to flash off quickly (I haven't timed it but I'd say it's easily under a minute).

As an alternative, you may want to apply a very dilute pickle stain to the bare wood and reduce the amount of color you're trying to get from the toner. That will reduce the pigment load in the toner and make it easier to spray evenly and avoid clumping at the same time. I find about an ounce of pigment per gallon of toner is plenty.



From the original questioner:
Thanks Paul. That is what I am talking about. I am trying to spray a toner, and when it gets too wet, it clumps. I will check into a smaller set. Meanwhile, I will decrease the amount of pigment. Toner... of course.


From Paul Snyder, forum technical advisor:
If you turn the fluid knob down pretty far, you can decrease the flow enough to atomize the toner well and avoid spraying too wet. Use whichever gun gives you the best/finest atomization.

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