Many finishers prefer lacquer to other materials for finishing wood furniture. It is durable but more subtle than varnish or polyurethane, and -- perhaps its greatest advantage over curing finishes like varnish -- it re-softens when you apply lacquer thinner. This softening property makes it possible to correct some defects in a lacquer finish or remove unwanted stains or blotches without resorting to sandpaper, which almost always requires application of a new finish and makes a mess.
Types of Lacquer
Nitrocellulose lacquer is manufactured by dissolving cotton in a solution of nitric and other acids and suspending the resulting emulsion in a powerful solvent. Nitrocellulose and acrylic lacquer, which is carried in a similar type of solvent, are the two types of lacquer that were most likely used on your cabinets. These finishes harden when the solvent evaporates, but they don't cure, like varnish, and readily emulsify when you apply more solvent. Some finishers apply catalyzed lacquer to kitchen cabinets. Unlike acrylic or nitrocellulose lacquer, it does cure as it dries, and won't emulsify when you apply thinner.
Repairing Non-Curing Lacquers
A simple test will tell you whether the lacquer finish on your cabinets or furniture has cured or not: rub a little lacquer thinner on an inconspicuous spot, and if the finish softens, it hasn't cured. You can then use lacquer thinner to correct a number of defects, including impact damage, scratches and cracking. The principle is simple: Applying the thinner directly to the defective finish emulsifies it so it can level into a new, defect-free surface and blend with the area around the damage. You can spray the thinner with a spray gun or dab it with a cotton swab onto individual scratches.
Sanding Off the Finish
If the finish doesn't soften when you rub it with lacquer thinner, the only repair procedure available to you is stripping, sanding and refinishing. Even during this procedure, having a supply of lacquer thinner by your side can make sanding easier. Wash the piece down with lacquer thinner after you're finished stripping to remove residue and prevent it from gumming up the sandpaper. If the wood has a stain, you can use lacquer thinner and a wire brush to clean much of it off. Using lacquer thinner in this way ensures that when you do sand, you won't have to remove extra finish or color.
Lacquer thinner contains a host of solvents, including acetone, toluol, methyl ethyl ketone, xylene, alcohol and naphtha. Some of these evaporate more quickly than others, and manufacturers mix them in different proportions to get different leveling and drying characteristics. These ingredients are highly flammable, volatile and noxious. You should never store lacquer thinner in an open container, nor should you use it near an open flame. It's important to wear a respirator and properly ventilate the room when working with it, because the chemicals can damage your nervous and respiratory systems.