Stains on wood floors are typically water marks, caused by spills or over-watering house plants. The area must be sanded, sometimes bleached, and then refinished to match the rest of the floor, which is the trickiest part. It’s a good idea to hire a professional for this work, particularly if the stain is in a highly visible area.

Typically, the process is as follows:

1) Sand the area with a vibrating sander, first with 100-grit sandpaper and then with 150-grit sandpaper.

2) Vacuum the area.

3) Wipe the area with mineral spirits for an oil-based stain and water for a latex stain.

4) For a dark stain, apply bleach or an oxalic-acid solution to lighten the stain, and then lightly sand with 150-grit sandpaper.

5) Mix up a stain to match the existing floor color. This process usually requires testing possibilities on a piece of wood that’s the same species as your floor. If you can’t find replacement pieces, cut them from a closet or another inconspicuous part of your existing floor and then replace that cutout with newer flooring.