How to test finish on Wood Flooring-Before Refinishing

If you plan to refinish your wood floor you’ll first have to determine what type of wood finish your floor is coated with. There are several candidates including polyurethane (most popular), shellac (least common), wax, lacquer and varnish.

Polyurethane
Use a cotton swap to apply acetone to the floor. If the acetone beads, you’re probably looking at a polyurethane finish. You can also test for polyurethane by using a coin to scratch a little of the finish. Polyurethane finishes will crumble as they’re scraped up

Shellac and Lacquer
Shellac and lacquer aren’t used in modern floor finishing, but floors that are older than the 1960s may have these finishes. To test your floor, use a coin or butter knife to scratch its surface. If the finish comes up in flakes, you’re probably dealing with shellac or lacquer. To distinguish which, rub a bit of denatured alcohol onto the area. If it dissolves quickly you’ve got a shellac finish. It may not dissolve all the way, instead becoming tacky and in that case you might be looking at a combination of shellac and lacquer. Test for the combination by applying a 50-50 mixture of lacquer thinner and denatured alcohol. If the finish completely dissolves, you’ve got a combination finish. Another way to test for lacquer is to apply a little lacquer thinner, if the flooring is lacquer finished it will turn rough and then become smooth again.

Wax
Apply a few drops of water onto your floor and then leave it for 10 minutes. If you come back to white spots under the drops of water, your floor has a wax finish. To remove the spots, dip steel wool into floor wax and gently rub the spots. If you don’t want to clean up the wax spots, there’s another test you can use. Just put a drop of mineral oil on the floor and wipe it up with a clean cloth after about three minutes. If there’s a brown-yellow residue on the cloth and it feels waxy, it’s a wax finish.

Varnish
Varnish cannot be fully dissolved, but you can test for its presence using denatured alcohol, which will partially dissolve the finish. Another test is to rub on lacquer thinner, which will cause it to crack and wrinkle up. If that happens, you’ve got a varnish.
o Use a cotton swap to apply acetone to the floor. If the acetone beads, you’re probably looking at a polyurethane finish. You can also test for polyurethane by using a coin to scratch a little of the finish. Polyurethane finishes will crumble as they’re scraped up.