Tweaking Viscosity for Good Flow-Out with Conversion Varnish
Getting a CV to behave right takes a delicate balance between thinner proportions and gun tip size. Here, pros describe the trial-and-error process they use to get it right. December 1, 2005
Question
I'm spraying ML Campbell resistant pigmented varnish and am having problems with it. It seems like it is too thick and it is drying too fast and air bubbles are not popping out. I have added up to 25% flow enhancer #2 and still have these problems. I started spraying with a Kremlin Airmix MXV gun and then switched to a Binks Mack 1 HVLP gun. I tried playing around with the atomization on the Binks gun, but nothing seems to work. The paint just doesn't seem to be flowing out right. I haven't added any thinner, other than the flow enhancer #2, because the can of flow enhancer says that it is used in place of lacquer thinner (something like that). I don't know what else to do. Any help would be greatly appreciated.
Forum Responses
(Finishing Forum)
From contributor B:
Have you timed the material in a #4 ford cup? I am going by memory, but I think you want something like 22-25 seconds. Anything longer and you need to thin it.
From contributor C:
I've sprayed a lot of Resistant with the Binks gun you have. Here's what works for us: catalyze 10%, then thin 22%, retarder 5%. Use the 94 fluid nozzle.
From contributor G:
That's one of the reasons I'm not fond of Resistant. In order to get it to the right viscosity to spray with my HVLP, I had to thin it 50% with Flow Enhancer plus the catalyst, which causes pigment floating. I think 25% reduction would give about 35 seconds in a Ford #4 - way too thick. You may be better going to an AAA and using the right tip.
From the original questioner:
I appreciate the advice. I called a finishing friend of mine and he told me to try the Kremlin air mix MVX gun again. This time I added app. 5% lacquer thinner to the paint, which already had 20% flow enhancer added to it. I set the red knob on the pump at app. 17 psi and I set the grey knob at app. 50 psi. This definitely helped, but it hasn't totally taken away the tiny air bubbles. The higher air pressure to the gun definitely helped atomize the fluid better, but I'm not to the point that I need to be at yet. Again, thanks for the help and any more help and advice would also be appreciated. P.S. I'm going to check the viscosity of the paint now. I have a Zahn cup. Does anybody know how many seconds it should take for my cup? I know you all mentioned a Ford #4 cup, but is it equivalent to my Zahn cup?
From contributor G:
Try this...
http://www.furniturefinishwizard.com/viscosityandwetmils.htm
From the original questioner:
I really appreciate the information. It was a big help. I am going to start checking my viscosity more often and I'm also going to check with my Kremlin rep to see what the recommended viscosity is for the tip that I have.
I've got a few other questions. What do you do if you have checked your viscosity and it is still too thick and you have added the maximum amount of thinner that the paint manufacturer recommends? Do you add more thinner anyway, or do something else? Also, I'm using ML Campbell's Resistant and Krystal. If I have put the maximum amount of Flow Enhancer #2 (20%) into the finish and it is still drying too fast, is it okay to add more Flow Enhancer #2 or is it okay to add some retarder to the mix? If so, what would be the maximum amount? And, could adding too many of these additives cause finish problems too?
From contributor M:
Here's our Resistant mixture.
For 32oz of product
3.2 oz catalyst (standard)
4oz flow enhancer
4oz care reducer
Set your fluid pressure at about 20 and your air as low as you can without getting the wings. This should work with any of the more standard size tips.
From contributor R:
If you have reached the max on the amount of thinner you can add and are still not getting good flow out, then you need to go to a larger nozzle/needle/air cap combo for the HVLP, or in the case of AAA, a larger tip. You adjust viscosity to accommodate the current temperature and the equipment setup that you are using. The solvents and the quantities you use now will likely change as the weather gets colder, or if you change the flow through of your equipment by using a different tip.
From contributor T:
The post above is right. I use 1.7 needle and 93P cap on my Binks HVLP. My reduction is only 20% of #2 flow enhancer and it flows out like milk!
