Flexner on Finishing: Finishes: They are A-changin’
Many years ago a friend explained to me the difference between woodworking tools and finishes. Woodworking tools, he said, are physics. You can see them. You can see that a band saw isn’t a table saw even though it has a table.
But finishes are chemistry. You can’t see chemistry. Varnish and lacquer, for example, look the same, both in the can and on the wood.
So there is much more opportunity for finishes to be confusing, especially when manufacturers misrepresent them and magazines publish contradictory information about them.
I think this description goes a long way toward explaining why the health problems associated with finish solvents are feared more than those that are obvious with woodworking tools (cutting off your fingers, for example). This, even though the infrequent, low-level exposure to solvents experienced by most amateurs is quite unlikely to cause any problems at all.
With this said, the particular solvents currently used in coatings (paints, finishes and stains) are changing, but you won’t “see” any differences. You will “feel” them, however, because they make the products dry faster, smell worse and may make them more viscous (thicker) – and more expensive.
So it will help your adjustment if you are aware of these changes so you recognize what is happening if a new can of the finish you’re used to behaves differently.
The impetus for the changes is to lower the volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) that are exhausted into the atmosphere.
All solvents are VOCs, which react in sunlight with nitrogen oxides to form ground-level ozone (smog). Nitrogen oxides are produced in high-temperature-combustion power plants and car and truck engines.
Some solvents, however, are so low in reactivity that they have been made “exempt” from VOC regulations. For coatings, these include primarily acetone, but also a few that are unfamiliar, including methyl acetate, parachlorobenzotrifluoride (PCBTF) and tert-butyl acetate (TBAc). You may see these listed on finishing products promoted as environmentally friendly.
Solvents that are considered health problems are called HAPs. Actually, it could be argued that all solvents are hazardous at some level of exposure, but some are more so than others.
Most solvents are restricted both as VOCs and HAPs, but there are some exceptions. The most notable is methylene chloride, the fast-acting stripping solvent. It is a HAP when used in large amounts, but it is exempt as a VOC. Therefore, high-volume refinish shops with employees come under OSHA restrictions, but everyone has access to high-percentage methylene-chloride strippers in small quart and gallon containers.
Articles: You’ll find many free finishing articles on our web site.
In our store: “Flexner on Finishing” – 12 years of columns illustrated with beautiful full-color images and updated, and “Wood Finishing 101.”
From the August 2012 issue #198
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