Flexner on Finishing: How to Choose a Finish
By Bob Flexner
At some point as you progress in woodworking, you begin to realize that there are many finishes to choose among; you probably ask yourself if you are using the best finish for your project.
Choosing is not as hard as it seems because there are only seven basic types of finish used by woodworkers: wax, oil, varnish (including polyurethane varnish), shellac, lacquer, water-based finish and catalyzed or two-part finish.
It gets easier. You can eliminate wax for almost all projects except small decorative objects such as turnings and carvings that aren’t handled much. Wax doesn’t work well as the sole finish because when buffed out thin, it isn’t water-resistant (only water-repellent) and grime gets ground into it when touched repeatedly by hands. (Wax is an excellent polish over another finish, however, because it adds shine and creates a slick surface that resists scratches.)
With wax out of consideration, you can then eliminate two more finishes based on the application tool you use: rag, brush or spray gun.
If you use a spray gun, you wouldn’t apply oil or varnish because they are very messy. They dry so slowly that the uncured overspray settles on and sticks to everything it comes in contact with.
Moreover, the appearance and durability of oil and varnish can be easily matched with faster-drying finishes. For example, an oil finish can be imitated with one or two thinned coats of a satin finish, and the superior durability of polyurethane varnish can be matched with any catalyzed finish.
If you use a rag or brush, you wouldn’t apply a catalyzed finish and you would rarely apply lacquer because of the fast drying and the strong odor of both. (Brushing lacquer, which dries more slowly, could be thought of as an exception.)
So if you use a spray gun, the choices are narrowed to four: shellac, lacquer, water-based finish and catalyzed finish. If you use a rag or brush, the choices are also narrowed to four: oil, varnish, shellac and water-based finish. Notice that shellac and water-based finish are the only ones applied both ways.
Choosing within each group of four then comes down primarily to choosing for protection and durability, application ease and color – usually in that order of importance.
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From the June 2013 issue #204
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