How Much Lacquer Thinner Should I Use?

Today, I was having a conversation with one of my customers about spraying a conversion varnish (Krystal, from M.L. Campbell) and the problems he was having with getting it to lay down nicely after it was sprayed. He said that he applied is wet enough to blend together and not be rough, but that he had a lot of orange peel in the finish. After discussing the possible causes of the orange peel it became obvious that he needed to add lacquer thinner to the mix, which he did not do.

This customer is new to spraying conversion varnish, which is a two-part mix that sets up and hardens chemically like epoxy, forming a super durable finish. The information on the can talked about the 10:1 ratio of finish to catalyst, but apparently didn’t mention a thing about thinning with lacquer thinner, so he used none. Even if it was mentioned, I assume that he was worried enough about getting the ratio correct (click here to learn how to easily get the proper mixing ratios) and not messing up the mix that he never imagined he could, or even that he should add lacquer thinner.

In this case, my customer was getting orange peel because the finish was too thick for his two-stage turbine. The kids at the finish distributor led him to believe that he shouldn’t need to add thinner, but they did not ask about the power of his spray equipment, assuming that he probably had a turbine strong enough to finely atomize the finish without thinning.

This Graco 2-quart pressure pot system I currently use is an older 2-stage model, but gives good results with proper thinning.

I continued to discuss the need to add thinner with my customer, and pointed out that a non-thinned finish requires more turbine power than he currently has. If he owned a 4-stage or 5-stage turbine, he could probably use the finish without thinner, but not with just a 2-stage. I speak from experience on this one, because my everyday gun is an older 2-stage model, and it requires at least a bit of thinning on almost everything I spray. I am okay with this apparent shortcoming because I am a proponent of applying multiple thin coats, as compared to fewer thick coats, which I believe are just inviting trouble.

As our conversation continued, he asked the million dollar question, “How much lacquer thinner do you add?” For me, the simple answer is, “Until it sprays good,” which is very ambiguous I know, but true. I have an advantage because I have sprayed more than him and I have an idea where I am headed, but I don’t truly know until I shoot a sample board with it and see how things are flowing (which I do every time before I spray the real thing). I spray a sample piece of wood standing up vertically to make sure that I can get a fully wet and flat surface with no runs or sags and to get a feel for how fast I need to move the gun to make all of that happen. If the sample surface looks good, I move on and spray the real thing. If I have issues, it is usually because the finish is a bit thick, so I add lacquer thinner until the finish sprays smoothly without orange peel and without runs.

A viscosity cup like this Ford 4 style, available from Highland Woodworking is a good starting point.

Another, more technical way to determine the correct amount of thinner is to use a viscosity cup. A viscosity cup is shaped like a funnel and determines how thick a fluid is by the time it takes to empty the cup. A thin fluid will empty in just a couple of seconds, while a thick fluid might take 30 seconds or more. When I started spraying and used a viscosity cup, about 15 seconds was the right amount for my gun, but it will vary from gun to gun. When learning to spray, I recommend using a viscosity cup and to follow the manufacturers recommendations. If nothing else, this will give you a good starting point from which you can make later changes and have a way to achieve consistent results. After you spray for a while, there will be less mystery, and you will know from one test shot what needs to be adjusted, even without the viscosity cup.

When my customer asked about adding lacquer thinner, I know he was worried about possibly adding too much, and after thinking about it, I don’t know that you can add too much. I can follow the logic that adding too much thinner may change the chemistry, but I mix the 10:1 ratio of conversion varnish to catalyst first and then add the thinner, so there should still be the same amount of resin and catalyst, just with more space between them, in the form of lacquer thinner which will quickly evaporate and let the two parts do their thing. Even with other lacquer products, which includes sealers, nitrocellulose lacquers and modified lacquers, I can’t think of any time that I have ever had a problem because I added too much thinner.

I’m sure finish manufacturers would disagree and warn you to not be so cavalier about it, but I sure wouldn’t worry about adding too much thinner. Simply add enough thinner until your spray gun is able to apply a nice, even and wet film that flows out flat and dries without sagging. Even if you do mix it a bit thin, feel confident knowing that you can always compensate by moving more quickly or reducing the amount of fluid coming out of the tip of the gun.

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About wunderwoods

Hi! My name is Scott Wunder and I am the owner of WunderWoods Custom Woodworking. We build wine cellars, built-ins and furniture from local woods, here in St. Louis, MO. Recently, I finished a three-year term as the President of the St. Louis Woodworkers Guild, which had me writing a monthly article for our newsletter. I love to write, especially about wood, and found that I still had more to say. Every day I run into something wood related that I realize some of my customers don't know and this seems like a great forum for sharing what I have learned (instead of telling the same story to each person). The main thing to remember is that I try to keep it light and as my wife always reminds people that have just met me, "He is joking."

11 responses to “How Much Lacquer Thinner Should I Use?”

  1. BKE says :

    Great blog scott. You ever talk about sanding swirls?

    • wunderwoods says :

      Thanks, Brian. I haven’t in a blog, but I am working on a finishing book and it will probably end up in there. Bad sanding is the #1 killer of otherwise good woodwork in the U.S.

    • mrz0420 says :

      Swirls are a result of your paper overloading or “damage” to the paper. Don’t be afraid to change paper constantly. Expensive I know but it works. Does it happen at all grits or just one size

  2. mrz0420 says :

    I have had the same problem we use RUDD brand from Sherman-Williams. And the rep says we should sand down to 180 only before spraying. He says the reason is that any finer sanding does not give the CV enough tooth to adhere to the wood and previous coats of CV it’s working for us we used to sand down to 320. So it’s a radical change in procedure for us but it’s working.

    • wunderwoods says :

      I sand no more than 150 (180 is acceptable) on raw wood and 320 grit between coats. 180 grit will definitely leave scratches between finish coats.

  3. Paintress says :

    Rather than using lacquer thinner , try using the flow addative which was designed for the conversion varnish & odd weather conditions. Many people are unaware of the 2 different flow addative’s 1 is for conversin varnish the other is for lacquers. There is NO flow additives for Cab Acrylics the Star addative is for the waterbased products. As for the polyuerthane & polyester line they vary depending on the weather. They aren’t as simplified as Ilva’s line is when it comes to those matters bet we all have our pro’s & con’s in life as I see it.

  4. Paintress says :

    Rudd lacquer & converson varnishes are NOT from Sherwin-Williams. They are an Seattle Washington independent Family owned company of over 100 years. I sold the line in Florida & spoke with the head of the sales dept, recently as Florida client wanted purchase to a 55 gallon drum of laquer. They are working with setting up a new distribution point in central Florida. It was a great selling product line, very high quality especially well suited to the extreme humidity and heat. Pricing levels were excellent as well. Lab support, customer support & service, were tremendous, can’t say enough wonderful things about them!

  5. Mike Robinson says :

    Is there also a conversion satin clear coat. That will give you that extra durable finish. Thanks Mike

  6. mrz0420 says :

    Well my partner says also that you MUST use a 1.1 atomizer and spray in fine coats a “wet mist” not flooding it. Has something to do with “melting” of previous coat and how it reacts at the chemical level. We spray 4 very light coats with about 10-15 minutes between before we sand ” between coats”. We are going to try to use retarder and see that works. I’ll keep in touch with our results.

  7. JLW says :

    ‘I am a proponent of applying multiple thin coats, as compared to fewer thick coats, which I believe are just inviting trouble.’

    Bingo babe

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