The relative wisdom of reducing nitrocellulose lacquer with the very hot solvent MEK is controversial. So… I thought I’d bring this up under it’s own heading.
I had reason to call Sherwin Williams this morning on an unrelated issue – the appropriate retarder to use with catalyzed vinyl clear. I ended up chatting with one of lab guys here in S/W’s Portland facility. I’ve talked to them before about my use of MEK in lacquer. But, it’d been quite some time so I figured I’d pose the question again just to see if they’d say something different.
Specifically, I asked if using MEK in any proportion would or could negatively affect any of the properties of nitro lacquer. I was told that reducing up to 20% with straight MEK was acceptable and wouldn’t affect any of the resulting film’s properties as designed to perform by Sherwin Williams. The S/W clear nitro lacquers are packaged ready to spray – meaning that no reduction is necessary. So, the acceptable 20% reduction with MEK would be above and beyond the solvents that are already in the lacquer.
Then I posed the same question albeit with the use of Acetone for further reduction. The lab guy was hesitant at this point. He didn’t give me an exact % figure (probably because I didn’t think to ask that specifically) but he did indicate that 20% would not be acceptable as it *could* affect the film properties. He was unsure and didn’t want to give me a concrete answer. I presume from this that, unlike with MEK, he had no practical experience using large quantities of Acetone with nitro lacquer.
Here’s the formula that I like to use with nitro lacquer: I reduce a total of aprox. 10%. Of that 10%… 70-90% is MEK and the remainder is PM Acetate (a slow drying solvent)… depending on the ambient conditions such as temperature and humidity. I have in the past reduced up to 20% using the same blend. But, I’ve found that the solids in the lacquer tend to settle out faster with that heavy of a reduction schedule and it requires stopping every half hour or so and restirring the lacquer.
Interestingly enough… the same MEK/PM Acetate reduction is acceptable with catalyzed vinyl clears too.
Anyway… my personal experience with nitro lacquers, both clear and pigmented, is that reducing it with MEK and PM Acetate is the single most valuable “trick” that I’ve ever learned. Once I got used to spraying lacquers with this solvent blend (MEK reduces the viscosity!), I’ve never, ever wanted to go back to using lacquer thinner. This stuff is sooooooo much more forgiving because of the inherent effects that MEK has on nitrocellulose.
Regards,
Kevin
Replies
wow! I think I am a wiser man today. I spray lac and have always used lac thinner. When you speak of Nitro lac are you talking about the same stuff you get off the shelf at paints stores and hardware store, like Deft.
When you speak of Nitro lac are you talking about the same stuff you get off the shelf at paints stores and hardware store, like Deft.
Well... yes and no. Yes, nitro lacquer is widely available in paint and I would assume hardware stores. But, the Deft lacquer, unless it's something other than what I'm thinking of, is actually an acrylic lacquer. That's why it doesn't yellow over time. And, since it's a brushable lacquer that means that they've already loaded it with some slow solvents. Acrylic and nitro lacquers without any slow solvents added should dry to the touch a little bit faster than the 30 minutes that Deft lacquer takes... something like 10 - 20 minutes @ 70 degrees (f) would be more typical of the lacquers that are designed strictly for spraying.
That said... the same solvent blend that I use with nitro lacquer also works very well with CAB (acrylic) lacquer. It will work with the Deft, but I wouldn't add the PM Acetate. Or if I did it would probably only be 5% max of the solvent blend being added. And I would try it out on something unvaluable first to get a feel for it. Being that the Deft is designed to also be brushable makes it a horse of a different color compared to the lacquers that I've used this blend with. It'd work. But, you'd definitely want to experiment a bit with whether to add the PM Acetate or not with that particular Deft lacquer.
The MEK is the solvent that's doing the real work on the lacquer. The PM Acetate is simply there to control and offset the less desirable side effects of using such a hot solvent.
Learning to adjust to using this solvent blend is part of making it work well and resulting in a great finish. I've learned to do what I like to call a "two-coat". What that means is that I'll spray the piece of furniture or cabinet or whatever with one medium wet coat. Once I'm done I immediately start over and respray it with a full wet coat of lacquer. The first coat is half flashed off before the second coat hits it and melts in. Being partially flashed off,the first coat will hold the second, wetter coat of lacquer in place. That means that in situations where a single full wet coat might result in sags or even runs, this two-coat procedure allows me to lay on that heavier coat without having to worry about it running or sagging unless I get carried away and put too much on of course. In all honesty this two-coat technique is half of my "trick" with lacquer. And it works the best when I also reduce with this same solvent blend. It'll work with regular lacquer thinner. But, it's more prone to orange peel and/or overspray problems when used with a lacquer thinner blend.
For anyone who has ever sprayed lacquer with a commercial heated airless system, this solvent blend is the closest I've ever come to replicating the way that a heated airless system will lay on those thick, flawless finishes without having to spend the $$$ that it would take to own a heated airless system.
Regards,
Kevin
That's great information! I will look forward to your future posts.
Jim
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