First, gently rub the damaged area with fine (220-grit) sandpaper. Don’t cut into the wood itself. Going too deep makes color-matching difficult: It strips off wood fibers that have changed color with age or stain.
After sanding, wipe away dust that could become trapped in the touch-up coat. Wipe well with a commercial cleaner formulated for polyurethane; these products contain ingredients that evaporate quickly so the moisture won’t affect the floor.
Reapply the Finish Coat
Brush on the polyurethane (use the same finish that’s already on the floor) with a foam paint pad, and then thin out the edges with a dry brush. Work outward from the center. Where the old surface wasn’t sufficiently sanded, some new finish may peel. A water-based finish will dry clear, while oil-based polyurethane will appear lighter at first but will darken with age. If the floor was stained, you will have to re-stain the sanded patch before applying polyurethane.
Wood Floor Problem: Light Scratches
Camouflage with wax sticks (available at hardware stores). They come in many different shades. Wood-stain markers (also at hardware stores) can be used for touch-ups.
Wood Floor Problem: Dark Spots
Remove minor ink, pet stains, and water marks with fine steel wool.
Wood Floor Problem: Chewing Gum, Crayon, and Wax
Cover the area for five minutes with a plastic bag filled with ice, and then scrape with a spoon or credit card. Follow with a commercial cleaner for polyurethane.
Wood Floor Problem: Oil or Grease
Wipe the area with a cloth dampened with a commercial cleaner for polyurethane.
Wood Floor Problem: Burns
Gently scrape away char with a putty knife, then spot-repair as you would for blemishes.