Q:
How can I identify the finish on a piece of furniture so that I can repair it?
Jack Simpson, Abilene, TX
A:
To know which finish you’re dealing with, try to dissolve it. Test a hidden spot. You’ll know the finish by which solvent removes it.
First, remove any wax on the surface by rubbing it with a cotton cloth dampened with mineral spirits.
Next, in an inconspicuous spot, place a drop of denatured alcohol on the surface, wait a few minutes, and then rub the area with a paper tissue. If the finish is shellac, you’ll rub some off. If the surface stays hard, repeat the test with a drop of lacquer thinner. If the surface becomes sticky, the finish is lacquer or a water-based finish. The latter was rarely used before the 1990s, so lacquer is the only candidate on older pieces.
If the surface remains undamaged by the lacquer thinner, you have a reactive finish such as varnish.
In the case of a shellac or solvent-based lacquer finish, a fresh coat of the same finish will melt into the existing finish, making repairs relatively simple if the existing finish is in good shape.
A fresh coat of a reactive finish, however, won’t chemically bond to an old coat, so you’ll either need to sand the existing surface to create a mechanical bond or, if the existing finish is too badly damaged, strip it entirely and start again from bare wood.
Fine Woodworking Recommended Products
Diablo ‘SandNet’ Sanding Discs
Odie's Oil
Osmo Polyx-Oil
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