Polyurethane is the modern way to finish a hardwood floor. It’s basically a plastic that is kept in suspension with a s solvent; once it’s applied, the solvent evaporates and you have a plastic coating on your floor. The older way to finish was with oil. Typically, that was a natural oil such as linseed or tung. Those are penetrating oils that work their way into the wood and provide a waterproof coating. Oil was used frequently until about fifty years ago. At that point, the switch to polyurethane began. However, oil has since experienced a resurgence. That means it can be difficult to determine if you have an oil-finished floor or a polyurethane floor.
Is It Smooth?
If your hardwood floor has been properly maintained, it should be smooth regardless of what the finish is. However, a polyurethane floor will be smooth like a piece of plastic. An oil-finished hardwood floor will feel like sanded wood. The difference is noticeable if you know how to compare them. For comparison, you should run your hand on a wooden cabinet or a kitchen table, as long as those aren’t unfinished wood. They’re likely coated in polyurethane. A wooden desk would suffice as well. Then touch your floor.
Does It Absorb Oil?
You can also choose to drop a tiny drop of oil in a hidden place. A linseed or tung oil finished hardwood floor will absorb linseed or tung oil. If you drop the oil on the floor and it simply beads up, you likely have a polyurethane or a lacquer finish on your floor.
What About Dish Soap?
Dish soap and oil do not mix. In fact, dish soap emulsifies the oil, which is why it’s so effective at cleaning greasy dishes. If you find a hidden spot of your floor, you can apply some dish soap with a sponge and rub it in. If you have a polyurethane finish on your floor, it won’t have much effect other than cleaning one spot of the floor. If it is an oil finish, the floor will feel rougher or drier than it did previously. That means that the dish soap has cleaned away the top layer of oil from your floor.
Lastly, you can use a tiny bit of nail polish remover. It won’t affect a polyurethane hardwood floor. A shellac or a varnish will turn tacky over time. The oil will get cleaned away by the acetone.