Problems spraying conversion varnish

      Troubleshooting cleanup and viscosity/load problems. September 2, 2002

Question
I have been spraying SW Kemvar for over 10 years and have never been able to resolve a couple issues. I spray with a pressure pot outfitted with a high pressure regulator set at 15 to 20 lbs based on mixture viscosity, a cheater valve on the air line, and run it through a Binks 2001 gun with a correctly sized fluid tip, needle, and air cap for conversion varnish. I tried a brand new Accuspray gun for a while but it sprayed a heavy band just below center, which was impossible to feather in reliably and I would get stripes on my finish, so I went back to the Binks. All material that goes in the pot is strained. I measure catalyst using a syringe graduated by the ounce. I am mainly having two problems, which may be related.

First, when reduced and sprayed per the SW spec sheet, I am getting what appears to be different viscosity loads even during the same spraying session. This problem is remedied if I over-thin, which I don't want to do as then I have to spray additional coats to achieve millage. This also causes sheen variation. My typical load is 1500cc Kemvar + 500cc lacquer thinner + 2 oz catalyst as the seal coat, then 1700cc Kemvar + 300 cc lacquer thinner + 2.5 oz catalyst as the topcoat. This is as thick as I dare, and as stated before, some loads seem thicker that others. I can be spraying a topcoat load and have everything working fine. Then when I reload with another topcoat, the gun will hardly spray it or won't spray it at all. Sometimes this problem clears up if I can keep spraying.

Second, it is impossible to keep the equipment clean. I use a pot liner (which did improve things), but everything downstream from there is a real battle. The sticky vapor gets up in the spring and ball in the regulator, causing it to malfunction (possibly why it won't spray), and the fluid hose keeps throwing off goobers which end up either in the tip, screwing up the fluid flow or atomization or both, or on the finished product. When I am done spraying I flush with lacquer thinner and then leave enough in the setup so there is a continuous column of thinner to the tip. I have even gone so far as to completely flush and clean everything between pot loads.

I have heard of people spraying Kemvar undiluted. Is this possible? It is not to spec. What benefit does it have? By the way, I used to thin with xylene but switched to lacquer thinner two years ago because it is a hotter solvent and I hoped it would help to keep the equipment cleaner.

Forum Responses
From contributor D:
You don't thin SW conversion varnish with lacquer thinner ever. You thin with Xylene. The other solvents present in lacquer thinner (primarily alcohols) are not compatible with conversion varnish. Also, I would not thin CV more than 15%. I don't use pressure pots so I can't comment on them. For CV, gravity feed guns are perfect, as the leftover CV is never a problem.



The above is right.

I used to spray the SW CV with a pot (no agitator), but stopped. The material settled out too readily in the hose and pot and I got different sheens unless I made a point of manually agitating. Possibly this is some of what is going on, especially if you are thinning so much. As stated, only with Xylene (or maybe High Flash Naptha 100 in warmer weather) and only 5% to 15%. I usually thin the SW CV about 5% with Xylene (or High Flash 100 if it's 80 or warmer).



Sounds like you're using a 2 quart pressure pot. That doesn't work so great with CV. Go to a 2 gallon pot and if you can afford it, spring for the agitated version. Anytime you spray CV with a pressure pot, eventually you get buildup in the fluid lines, which comes off in a grit and usually waits till you're spraying topcoat to come out. You can clean them successfully a few times, but eventually you will get buildup. What I do if I have to use the pressure pot for a big job is flush out the line real well when done, replace with a new fluid line and use the old one for primers or oil finishes.


Never used that finish, but as far as the pressure pot goes, I had the same problem. Take the regulator off of the head of the pot and put it on the other side of air infeed. This will keep blow back and vapors from freezing up the regulator.

Also seems like all the conversion varnishes settle quickly, causing sheen differences. We make sure only to mix enough to spray immediately. If sitting for more than 45 minutes, we take the time to pop the lid and agitate again. It's worth the 5 minutes to re-agitate than to spend the hours to re-shoot it.



The above is right about the lacquer thinner, and if memory serves me right, SW was very specific about using xylene with their product, also suggesting that I not use acetone either. I used acetone with another vendor's product, and was told I probably could, but that they didn't suggest it with theirs.

This stuff should not be allowed to settle for very long, as mentioned above. I am a real chicken when it comes to spraying CV, and shoot only qt. cups, stirring the brew constantly. And yes, forever flushing the gun and wiping tips and siphon tubes. Worse when using sealer.

I too usually use the stuff direct from the can with no thinning. Hasn't been a problem for me... yet.



From the original questioner:
This has clarified some of my questions and made some others more confusing. What has been clarified is that the product needs to be agitated during spraying and the fluid lines need to be replaced frequently. What is unclear is the thinning and the equipment used to spray undiluted.

I have the Sherwin Williams product data sheet CC-F17A dated 5/88, which states "Catalyzation and Reduction: As a sealer - Catalyze with 3% catalyst by volume then reduce up to 50% with toluene or xylene. As a topcoat - Catalyze with 3% catalyst by volume then reduce up to 25% with toluene, xylene, or high flash naptha. The slower evaporating solvent is necessary for best flow and leveling on open grain woods such as oak and mahogany."

Is this data sheet at fault? I have tried to spray undiluted and the atomization is so poor that the material won't dry for days. What would be the difference between a 2 qt pressure pot and a 2 gal pressure pot? Is a Kremlin pump a better system for conversion varnish? Does anyone flush and store their lines with uncatalyzed product? Does that dilute the catalyst in the lines to the point of preventing buildup? What are your opinions on offering lacquer finish at a base price with the option of upgrading to conversion varnish for a substantial up-charge? Would your customers accept this?



From contributor D:
1988 was a long time ago. The current Chemical Coatings Catalog shows the reduction for use as a sealer to be 25% and for topcoat a maximum of 15%. You should be easily able to spray at packaged viscosity with sufficient air pressure. I can, using my SATA Nr2000 gravity guns (but I premix all of my C-V at a 15% reduction so that I can use it both as a sealer and a topcoat without thinking about it). Accounting for the reduction, I then catalyze at 2.6%.

An Airmix vs a pressure pot is like comparing a BMW to a Ford Escort.

If it's furniture, pre-cat is fine. If it's kitchen cabinets, you have to use C-V for the rigors of that application. There is no choice.



From the original questioner:
I just read a thread further down on the forum concerning the Astro guns. My situation is that of a custom woodworker and cabinetmaker doing high end work in a remote area. There are few finish shops and not enough money so I like to finish my own work to keep the quality high and the dollars in house. I have found that CV leaves a beautiful finish on everything I put it on and the Binks equipment works great. It's just the tenacious nature of CV, I guess, that causes the problems. As I am the manufacturer, I try to flat finish everything I can before assembly. The gravity feed guns would be hard on my wrist and shoulder, it seems.


Why not switch to a conversion varnish that does not have this tendency to settle out as much as the Sherwin-Williams conversion varnish does? Mixing becomes less of a worry.

I used CCI once (they are an RPM company from Hudson, NC) and not only did I not have to worry that much about agitation, the finish department at a major Kitchen & Bath cabinet company (DutchMade - sp?) told me that they never concerned themselves with the Aristocoat settling out either.

Pigmented coatings are different, as they will always need to be agitated. But coatings with flatting agent ground in them (like CCI's Aristocoat) were not a problem for me at all.

I understand that there's a difference between a coating that has flatting agent in it and mixed in suspension and a coating that has the flatting agent ground in to actually keep the flatting reasonably well dispersed in suspension.

Another possible option for you is stepping down (or over) and switching to a catalyzed lacquer like M. L. Campbell's Duravar or their non-yellowing conversion coating Krystal. Both of these thin with lacquer thinner and they just seem so off-the-shelf customer-friendly and easy-to-use.



The 2 Binks 2 quart pot has the little cheap spring and valve setup that likes to clog so efficiently. The 2 gal pot does not. I use Toluene with CV and have no problems.


From contributor D:
Toluene, Xylene and High Flash Naptha are all from the same chemical family. These are called the aromatics. They can be used interchangeably depending on the evaporation rate you need for the weather of the day. Tolulene has an evaporation rate of 4, Xylene's rate is 11, and High Flash Naptha (Solvesso 100) has an evaporation rate of 40. If you need more open time for flow out, you go with the High Flash Naptha. If you need a quick dry, then Toluene is the way to go. This is what's great about solvent finishes.


Then you are undercatalyzing. I understand - first to add 3% cat and then 15% thinner... or am I wrong?


From contributor D:
As you correctly state, it's a 3% catalyzation of the un-thinned material. However, if you pre-thin (as I do), you've increased the volume of the CV, but not its concentration. In 1 gallon of unthinned CV you would add 4 ounces (3%) of catalyst. If you thin the CV 15% first, then in a gallon of the pre-thinned CV you actually only have 85% of 128 ounces of CV. This is 108.8 ounces of CV. 3% of 108.8 ounces = 3.264 ounces of catalyst needed. However, the true volume of the *thinned* CV is 128 ounces, so 3.264/128 = 2.6% as the proper catalyzation of the thinned CV, since you don't catalyze the inactive solvent (Xylene) used to thin the CV mixture. Simple, isn't it?


One other thought on the original post: If you are flushing your lines with lacquer thinner (not cleaning out completely), that could be causing the hunks of finish that come out of the hose. The thinner causes the CV to gel up on the inside of the hose and the flow of liquid works it loose. Running the right thinner should help that part of the problem.


You bet your life it does. Desperate measures today. Hot and humid, everything gunked up. Catalyzed in the cup and siphon. Don't do this at home! Had to run stripper through the gun to clear out everything.

Contributor D, you say you have had adhesion problems in the past. What was happening?



From contributor D:
The problem has to do with the high solids nature of CV. I always thin my CV 15% and the reason for this is to prevent bridging of the pores of the wood (a particularly nasty problem on red oak) and to force the CV to penetrate into the wood so that you get good adhesion. I've also had SW vinyl sealer suffer from adhesion issues. The key to the first coat is penetration. The coating can't simply lie on top of the wood - it has to bond to it. The problem is the coatings companies have to meet VOC restrictions. To do this they need to limit the VOCs (thinners) in the coatings. So they recommend (at least in print) that you don't thin their material so that you don't increase the VOC content. In reality you *must thin the material* or it sprays like crap and it doesn't adhere very well either. A sealer coat should never be sprayed at more than a 15-20 second timing in a Zahn #2. Anything slower is too thick.

I live in the hottest city in America. This is why I use gravity guns. You put the material into the cup. Add catalyst, spray what you need, pour the unused material out and put it in a refrigerator. Pour Xylene into the cup, swish around and shoot out for five seconds and these problems don't occur. When you want to spray CV again, you pour the Xylene from the cup into a mason jar, cap it, pour the refrigerated CV back into it and so on and so forth. I'm telling you - pressure pots suck. Gravity feed rules! Every decent auto body man in America uses a gravity feed gun. It's not an accident.



From the original questioner:
So you're saying that the only solution is to hold up a cup full of material at arm's length the entire time I am spraying. My typical job would have 60 to 100 doors and drawer fronts with misc trims. I went to a remote pot to get away from this. Also, I was having the problem of buildup with xylene - that is why I went to flushing with lacquer thinner, which improved things only slightly. I can't go back to lacquer because my finish is an integral part of what my customers expect from me. Just live with the situation, I guess. By the way, I put Kemvar over vinyl sealer once and had the finish lift after the application of a second topcoat. No more vinyl sealer for me.


From contributor D:
Have you ever used a gravity gun? True, they might look weird to somebody who's never used one, but they are *much* better balanced than a typical siphon feed cup gun. It's not as bad as you make it sound. They also refill far faster than cup guns. Don't knock it until you've tried it.


A slow high-quality lacquer thinner will clean equipment far better than a cheap hot thinner. We spray CV out of a similar 2 quart pressure pot with no problems. Gravity guns are the way to go on small to medium size jobs.


If you are doing the volume like I think, look at the Kremlin airmix. Have a demo from a rep. Once you see it in operation, you won't see how you made it without one. Of course, if you are using CV, flushing out is mandatory, as it is with a pot. Also, unless you have a stainless steel pot, you may experience yellowing of the CV or any acid catalyzed product. Not so with the Kremlin.


From the original questioner:
I have not used a gravity fed gun yet but I will be getting one of those Astros based on the posts about their abilities for small/quick jobs. It's the long spray sessions where I want as little weight in my hand as possible that I would like to keep using a remote pot. A bunch of friends all bought Kremlins and I have tried out one but I have found the performance similar to my current setup (control over fluid and atomizing air/overspray).


We have always used gravity guns with 1 qt stainless cups. Just a few ounces of thinner or xylene and a toothbrush to clean the tip and your cleanup is finished. 1 qt cup is a little slower, but not the hassle of pressure pots. Never did like a pressure pot for CV.


I believe contributor D does not do large volume jobs - that's why gravity feeds fill the bill for him.

100 doors will require a pump system or large pressure pots. Any type of production finishing I have ever seen has only gravity guns for "off line work" or in small polyester shops they use gravity feed guns also. It all depends what you require to get the job done.

Bob Niemeyer, forum technical advisor



From contributor D:
Bob, I agree with you with respect to large volume users using Airmix systems. My point is that 2 quart pressure pots to me are next to useless. My gravity feeds hold a liter, which is more than half of what a two quart pot system does. The SATA design is very well balanced. With the two quart pot you need to hold the pot in one hand and the gun in the other. With gravity, one hand is free. If I were doing production work, it's strictly Airmix. However, I maintain that if you are using catalyzed materials, pressure pots aren't where it's at, especially 2 quart pressure pots. Either go with the Airmix (clearly the best choice) or use gravity.


From the original questioner:
I put my 2 qt. pot inside the small cabinet I use as a pedestal for the lazy susan and run about 15 ft of lines to the gun, so I can use it one-handed. It is fast and easy, but the fluid line builds up debris, which is what started this thread.


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

Comment from contributor A:
When I have an extra worker around we can easily spray 40 doors in 20 minutes, with him taking them off the door rack and replacing them back. Alone I can spray 20 doors in 25 minutes unless I'm having the problems you seem to be having. The point is, the product doesn't sit in either my gravity feed gun or syhpon guns more than 25 minutes. All the advice is solid above. I've sprung for new guns (Binks) and new lines when I get the occasional $30,000 job. So what's a new line worth to you? A $20,000 job? A $10,000 job? I now have 2 good Binks syphon feeds and a new gravity feed gun for top coating and 3 Binks guns for first and second coating. Sounds extravagent? Not when you consider the time it takes either you or your employee to rub out and repspray a job. I have a friend who has a smaller cabinet shop that shoots CV a couple of quarts at a time through an airless sprayer. It's a nice enough finish for the average home, not good enough for an architect or owner who wants a really good finish.

Since you're spraying up to 100 units at a time, that's all the more reason to spend on new lines occasionally, or always on a job that size. You can afford it if your finish is your signature - you should put a premium on your end price. Not a substantial one, just big enough that you continue to get the jobs while people appreciate your superior finish.



Comment from contributor B:
I used to shoot a lot of conversion varnish, both clear and tinted. Both the sealer and the finish have different catalyzsts and different percentages to add. Always catalyze first and then dilute (10%). Remember, there is a pot life with this stuff. I think 24 hours? Also very important is temperature. If not at a constant correct temp, all sorts of things can happen. Also very important is atomization. I use an AccuSpray 240C, with a 10 cap and 51 tip. The 4 stage machine produces 8-10 psi.


Comment from contributor V:
Depending on the size of the operation, I feel a gravity feed gun is the best method. I work for a cabinet shop and have been using C/V for a while now. It gives a very durable finish with minimal coats. I have had similar problems with different sheens and almost always it is because of settling of the finish. As far as thinning, I do not. At times I will add Flash Off to eliminate overspray. I know that HVLP is the new rage, but I prefer a gravity feed gun with high pressure(60 psi to 80 psi) or the air assisted airless systems. Pressure pots with C/V are very tricky if you are using over a prolonged time.


Comment from contributor I:
Sherwin William's high flash naptha is the only way to go with Kem Var. Do not use regular VM&P naptha - you must ask for #100 Naptha, a.k.a. R2K5. I thin 25 - 30% and spray using HVLP equipment. Xylene's drying curve is way too slow and you get a dry, crusty, banded finish, whereas R2K5 levels out beautifully, yet dries quickly. This works in both hot, humid weather and even better in cold, dry air.


Comment from contributor J:
I have been spraying cv for about 15 years and although everyone is saying not to use lacquer thinner as a solvent I have had nothing but positive results. It's much less expensive and itís hot which keeps the line clean and it dries faster as well. I spray with a Kremlin 10-14 pump and a Kremlin SX gun.


Comment from contributor E:
I'm a first time user of SW Kem-var CV and I recently sprayed a large kitchen with a lot of cabinets, and all of my trim and casing, and doors. I'm doing solid oak 6" base 3/4" thick 1x4 casing solid oak doors. I mixed 64 oz of CV with 64 oz of xylene and 1.9 oz of cat. I'm used to doing all woodwork (15 to 20 years ago) with the Lacquer stain then sealer then two coats of finish. Lacquer has changed since then and I don't like the new stuff. Now I'm spraying CV with my Graco airless with a 211 tip and I like it. When I sprayed it worked out great, and laid out nice after mixing up 4 batches then cleaning it out with xylene through my airless. It seems to me this is how it should be. I'll probably mix my finish at 64oz cv to 32oz of xylene and 1.9 cat. The only drawback is it burns the eyes really bad.



Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?


Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Finishing

  • KnowledgeBase: Finishing: General Wood Finishing

  • KnowledgeBase: Finishing: High Speed Production

  • KnowledgeBase: Finishing: Refinishing

  • KnowledgeBase: Knowledge Base


    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.



    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2016 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB











  • WOODWEB - the leading resource for professional woodworkers


      Home » Knowledge Base » Knowledge Base Article