Thinning Opaque Finishes

Tips and tricks for thinning your formula when you go from clear to opaque finishes. June 17, 2010

I hope someone can help. I use Mohawk's clear CV with a 5% reduction with great results. I am now getting a white painted job using their ultra white CV. I started out with a 5% reduction and it sprayed and looked bad. I have practiced on scraps, increasing the reduction in 5% increments. I am now up to a 20% reduction that still has orange peel. I'm not sure if I should keep adding more solvent. I am spraying with a Binks Mach 1 HVLP and a 2 gallon pot. I also use a 1.4 fluid tip with a 94p air cap. My pressures are 6lbs for the fluid and 35-40 for the air.

Forum Responses
(Finishing Forum)
From contributor W:
What kind of thinner do you use? The right thinner will quickly reduce your viscosity with only small reduction. You can try to use buthyl acetate as a solvent. In my experience this solvent works for a lot of finishing materials. And always check the viscosity, whenever you do your reduction, until you find the right viscosity.

From contributor R:
What is the temperature in your shop? Temperature is very critical in relation to viscosity. The colder the temp, the higher the viscosity and more potential for orange peel. The 1.4 tip sounds too small to me. I think a 1.8 would be better. You can also increase your atomizing air pressure. Your pressure gauge for the fluid probably isn't very accurate at 6 PSI. What I would always do is turn off the atomizing air, trigger the gun and watch the stream of material coming out. It should only go 3-4 feet in an arc.

From contributor C:
You say you're using Mohawk CV with a 5% reduction - what is the solvent/diluent that you're adding and is it from Mohawk? (Check the can or MSDS sheet online.) Any pigmented finish will have a higher (thicker) viscosity than a clear of the same type. In nitro it's not uncommon to dilute the pigmented lacquer 50/50, not that this would be necessarily so with a CV.

Most CVs respond well to 150 flash naphtha to help lay out the pigmented or clear variety. I don't agree with contributor W about the butyl cellosolve or other ethyl ethers for thinning an alkyd amino resin based product. BC is the main lacquer solvent. It has been the standard since the 30's. Before that it was fusel oil amyl acetate or what's known now as natural amyl acetate.

Many cellulose nitrate diluents and thinners can be added to other than nitro lacquers with varying degrees of compatibility that may be acceptable as far as not knocking any resins out of solution into a milky mass (adding MS in nitro and stirring), but it doesn't mean it's the best choice.

There were millions of hours spent experimenting in the 30's and 40's, with lacquer as well as the bulk of the other coatings we now use. Regarding the effects on the resins, all things were considered and studied - molecular weight, boiling points, evaporation rates, vapor pressures, heat of evaporation in calories per gram, solubility of material per 100 cc's of water at 20 Celsius (and also the opposite), specific gravities, etc.

Then you have tolerance levels of any single given aromatic or aliphatic hydrocarbon that you can put into any particular resin being formulated. Too much of one or the other can affect the resins present in the mix in all the above categories, either positively or negatively.

It has long been known, for example, that alkyd resins reduce their tolerance of butyl acetate with other solvents and diluents for the largest part from 2.7 to 2.0 and with ones in which they don't - they increase the tolerance level from 2.7 to as much as 3.5. When using to thin an alkyd amino (that may contain small amounts of other copolymers and properly known amounts of other hydrocarbon mixes) - who knows?

Bottom line is, unless you know how the diluent/thinner is going to react in the coating, you're better off using those that are recommended by your supplier.

P.S. Contributor R is right on all accounts - take his advice. Also, Devilbiss sells a pressure gauge that's great for pots. 1 turn = 1lb increase/decrease. This will keep your air and readings extremely stable

From Paul Snyder, forum technical advisor:
I haven't used that product, but I have used other brands with similar characteristics. My preference is to thin the material until the viscosity is in the range that works well with the spray equipment I'm using. If you don't have a viscosity cup, you should be able to get a $10 Ford #4 from your coatings supplier. There's a description of how to use one at the link below.

I also use the Mach 1 with a 1.4 for a great deal of the work we do. We spray everything but primer with this gun, including latex paint. For primer, we use a gun with a 1.6 needle. The larger needle allows thicker material to go through the gun but doesn't atomize as finely as the 1.4.

6 lbs for the fluid sounds pretty low and you could go just a little higher with the atomization if you need to. We use about 20 PSI fluid and 45 PSI atomization for the thicker finishes. Like contributor R recommends, just adjust the fluid pressure to the flow rate you're comfortable with.

Measuring Viscosity

From the original questioner:
Thank you for the quick response. The thinner I am using is a blend from Mohawk called reducer/retarder. I think I might need to thin it more. I had earlier reduced it in 5% increments and the look improved. And it is kind of cold, about 65 degrees.

From contributor C:
Is that the recommended thinner for the product you're using? Or just something you ordered for other coatings as well like lacquers?

From contributor B:
Spraying an opaque coating is a little different than the clears you're used to spraying. Just check out how thick the Mohawk Ultra White CV is compared to the Mohawk Clear. Look at page 54/55 in the Mohawk Catalog. The Ultra White CV is a 68% solid by weight... Says it's not necessary to reduce, and it should read 47-49 seconds in a #4 Ford cup. On page 54 it says that the correct reducer for thinning is M650-1057 Conversion Varnish Reducer. Kinda confusing, isn't it? Should I thin it or should I not thin it?

In order to meet the 550 max VOC, you should use it right out of the can; if you add thinner, you exceed the max VOC limit. I suppose if you were using an atomic activated fire hose to apply it... it might work. In the real world, you really have to reduce the product until you're happy with the way it leaves the gun and the way it flows out, once it lands on whatever you're spraying it on.

Everyone has different distances that they spray and different speeds in which they spray and the temperature of your spraying environment might be different than someone else's. It boils down to experimenting until you are happy with the results. This product, like most others, should not exceed 4 dry mils. Dry mils are way different than wet mils, so you have some room for your testing.

Let's discuss the Ultra Clear Conversion Varnish. Those specs are on page 52/53. The clear has a 44% solid by weight, a viscosity reading of 16-18 seconds in a #4 Ford cup. If thinning is necessary you can use acetone M650-001 or M650-1057 Conversion Varnish Reducer/Retarder.

44% solids vs 68%solids is a huge difference and 16-18 seconds vs 47-49 is just as huge. My guess is, if you scoot up the air/material settings on your pressure pot and thin out the material some more, your results will improve.

From the original questioner:
Thanks again. You are right about the clear and pigmented not working the same way. I am positive that I have the correct reducer for the CV I am using. I just need to play with it a little more.