UNDERSTANDING LACQUER THINNER
If you spray any type of lacquer – nitrocellulose, CAB-acrylic, or catalyzed – you use lacquer thinner for thinning; and cleaning up. Of all thinners, lacquer thinner is the most versatile and also the most complex. Other thinners, such as mineral spirits (paint thinner), naphtha, acetone, and methanol, are simply the single solvent, so their characteristics don’t vary. Lacquer thinner is a combination of solvents chosen by manufacturers from different solvent families to give each thinner specific characteristics.
Since types and brands of lacquer thinner differ depending on how they’re made, you will gain much better control of your finishing, and experience fewer problems, if you know how to choose between lacquer thinners.
There are two key variables in the make up of lacquer thinner the amount of each type of solvent used (dissolving and diluting), and the evaporation rate of the particular solvents used.
Types of Solvents
As you’ve surely noticed, it doesn’t take much of the right solvent or solvents to soften or damage lacquer. But it takes a lot of solvent to thin lacquer. Manufacturers take advantage of this characteristic to keep down the price. They blend the expensive dissolving solvents with cheaper diluting solvents.
The only thing you really need to know about solvents is that within each family they differ in evaporation rate. Manufacturers choose between these solvents to control how fast the lacquer thinner evaporates out of the lacquer film.
To thin lacquer, lacquer thinner has to be formulated properly. It has to have enough dissolving solvent to put the lacquer totally into solution or the sprayed lacquer will resemble tiny pieces of white cotton. This is called “cotton blush” or “kick out.” Lacquer thinner sold for clean up usually has too low a percentage of dissolving solvent to put lacquer into solution.
Lacquer thinner made from reclaimed solvents is also risky to use for thinning lacquer. Since the reclaimed solvents vary from batch to batch, the thinner may work well one time and not well the next.
Speed of Evaporation
All lacquer thinners contain solvents with differing evaporation rates so that running and sagging are reduced. But lacquer thinners vary significantly in the time it takes for total evaporation depending on the particular dissolving solvents used.
Over-the-counter lacquer thinners are commonly divided into three groups: standard lacquer thinner which evaporates at “normal” speed, lacquer retarder which evaporates more slowly than standard lacquer thinner, and fast lacquer thinner which evaporates faster than standard lacquer thinner.
Standard lacquer thinner and lacquer retarder should be available from all lacquer suppliers. Fast lacquer thinner is not so widely used for wood finishing, and is usually carried by auto-body paint stores.
In normal weather (75°and 40% humidity), standard lacquer thinner evaporates about right. In very hot weather standard lacquer thinner won’t give lacquer time to flow out level before it dries. The lacquer may even dry in the air before it lands on the wood resulting in a sandy surface called “dry spray.” If the weather is humid, moisture becomes trapped in the lacquer causing it to appear milky. This is called “blushing.” You can solve all three problems (poor flow out, dry spray, and blushing) by using lacquer retarder or by blending lacquer retarder with standard lacquer thinner. (If you live in a very humid climate and the brand of lacquer retarder you are using isn’t slow evaporating enough to prevent blushing, switch to a brand, like M.L. Campbell’s C163 36 BC Super Retarder.)
No matter which type of lacquer thinner or blend of thinners you use, continue with the same ratio of thinner to lacquer. The amount of thinner required for optimum atomization is not affected by the speed the thinner evaporates from the applied film.
[NOTE: M.L. Campbell is one of very few companies that provides an environmentally - friendly lacquer retarder – C161 1 Care Lacquer Retarder. This thinner is made entirely from premium-quality ester and glycol-ether solvents. No polluting HAPs, such as ketones or petroleum distillates, are added to reduce cost.]
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