Q:

I just moved into a new house with hardwood floors throughout. I’ve heard that it’s important to tailor cleaning methods to the type of finish on the floor, but I have no idea what finish was applied by the previous owner. Are there any tricks to finding out?

Meg via email, None

A:

Finishing expert Peter Gedrys replies: One of the first questions I would ask is about the age of the existing finish. If the floor was installed and finished or simply refinished within the past 10 years, it’s probably covered with a polyurethane of some type. That said, it could be an oil or waterborne urethane, the latter of which have become popular for their lack of solvent odor and fast-drying properties. A few other possibilities would be a varnish, shellac (although you rarely find floors refinished with shellac anymore) or a thin wiping varnish commonly known as a danish oil.

There are a few common solvents that you can apply to the existing finish to help determine its type, but your first priority is to clean the test area thoroughly. Find an inconspicuous area, and wash the floor with some mild soap—dishwashing detergent works well—and warm water. Wash and dry the area until your paper towels no longer have any dirt residue on them.

To test the finish, you’ll need a little mineral oil (baby oil) and three solvents: denatured alcohol, lacquer thinner, and xylene. Using these solvents requires gloves and good ventilation, and it doesn’t hurt to have on a pair of safety glasses, either.

To begin, put a few drops of mineral oil on your cleaned spot. If the oil tends to soak in, it means your floors are finished with a very thin wiping varnish. If the oil readily beads up and wipes away easily, then you have a film finish such as shellac or a varnish. The type of film finish will be determined in the next steps, using the solvents. These solvents must be applied in a specific order (from least aggressive to most aggressive).

Start by applying a few drops of denatured alcohol to the surface of the floor. If the surface softens and gets sticky to the touch within a minute or so, your finish is shellac. If nothing happens, wipe off the alcohol and apply some lacquer thinner, which softens both shellacs and waterborne coatings but won’t have a pronounced effect on an oil-based coating such as a urethane, alkyd, or phenolic varnish. If the lacquer thinner softens the finish, you can follow up with a more conclusive test by applying a few drops of xylene to another spot. If the xylene removes the coating, then your floors are finished with a waterborne coating. If it doesn’t, you have an oil finish.