|Test your knowledge with this quick quiz|
1. False. For example, acetone is not classified as a VOC. It is commonly added to stains and finishes by manufacturers to bring their products into legal compliance.
2. False. Water-based lacquer is a misleading name used by some manufacturers to make you think their water-based finish is similar to nitrocellulose lacquer. In fact, water-based finishes are based on an entirely different chemistry and have very different characteristics than nitrocellulose lacquer.
3. True. These are the methods because the primary cause of orange peel is spraying too thick a liquid with too little air pressure.
4. True. With a reflection, you’ll see runs, orange peel and dirt, and can make adjustments before you have covered the entire surface with these defects.
5. False. The first coat of any finish seals the wood, so special products aren’t needed for sealing. So-called “sealers” have other purposes. For example, sanding sealers make sanding easier. Vinyl sealers prevent color shift when used between an NGR dye and a catalyzed finish. Vinyl sealers can also be used to get around the application window of conversion varnish so color steps can be added.
6. False. A washcoat is a thinned coat of sealer or finish (usually 10 percent solids or less) applied under a stain to reduce blotching, or between color coats to add depth and keep the colors from running together.
7. True. Wiping leaves more colorant in pores and soft areas so they show darker and are highlighted. Spraying and not wiping puts an even amount of color everywhere.
8. True. Most are thinned varnish that, unlike tung oil, cures hard so it can be built up to a thickness on the wood. Real tung oil is usually labeled “100 percent tung oil,” contains no petroleum distillate, and has a very distinct nutty odor.
9. True. Lacquer and shellac (evaporative) dry entirely by the evaporation of their solvents and can be redissolved by their solvents. Alkyd varnish, polyurethane varnish and all two-part finishes (reactive) cure by a crosslinked chemical reaction that leaves the film very resistant to solvents, heat and abrasion. One-part water-based finishes (coalescing) cure partly by solvent evaporation and partly by chemical reaction, leaving the film more resistant than evaporative finishes, but less durable than reactive finishes.
10. False. All stains cause blotching on hardwoods if the wood itself is prone to blotching (primarily tight-grained woods such as cherry and numerous “white” woods). You can reduce blotching on these woods by applying a washcoat under the stain or by spraying a “no-wipe” stain, which is a stain thinned three- or four-to-one with thinner and not wiped off.
11. False. The cheap guns don’t atomize as well, so orange peel is worse. These guns do work well, however, for spraying stains, glazes and paste wood fillers that you will wipe off.
12. True. You should apply no more than two or three coats of conversion varnish — not more than five dry mils (thousands of an inch) total — or you risk the finish cracking in random directions.
13. False. Catalyzed lacquer is an entirely different chemistry. It is based primarily on melamine and urea-formaldehyde resins with only a little nitrocellulose added.
14. False. Only the topmost coat is responsible for the sheen. Flatting agents work at the very surface of the finish by creating a microscopic roughness that reflects light randomly. The more flatting agent added to a finish, the greater the roughness and the flatter the sheen, but buried coats have no impact.
15. False. “HVLP” (high volume, low pressure) refers to any spray gun that uses a high volume of air rather than high-pressure air to atomize a finish. Most compressor spray guns sold today convert compressed air to high volume air and produce the same soft spray with reduced bounce back as do turbine guns. So these compressed-air guns are also HVLP.
16. True. Acetone is the fastest evaporating commonly available solvent for lacquer. The solvent evaporates very quickly, leaving a thinner film that then hardens faster.
17. False. It’s much quicker and less work to fill pores using paste wood filler. For oil-based fillers, apply stain first, then a washcoat and then the filler. Let it haze and then wipe off the excess across the grain.
18. True. And, unfortunately, there’s very little you can do about it.
19. False. It’s much more effective to slow the drying of the finish by adding some retarder. Overspray then has time to settle and dissolve into the finish before either dries.
20. True. The cause of a split spray pattern is too much air (pressure or volume) pushing the finish out to the ends.
Bob Flexner is author of “Understanding Wood Finishing.”