How to Mask a Dark Stain on Wood Flooring

Set up your drum sander with its heavy sanding belt. Turn on the sander with the surface of the belt raised off the floor (either by tilting it back or raising the lever that holds it up, depending on your model of sander). Lower the belt to the floor and immediately begin moving the sander up and back with the direction of the floorboards.

Move the sander forward and back repeatedly while gradually moving to the side. Sand the whole floor, with the direction of the floorboards, taking up the surface gloss and some of the stain. Don't let the sander stand in one place while it's running, as it will gouge the floor. Vacuum up the dust.

Sand the floor a second time using the medium sandpaper belt, again keeping it with the direction of the floorboards. This should take off the upper layers of the stain, exposing the bare wood. (Note: If the darkest stained area isn't completely gone, don't try to sand down into it more, as you can ruin the floor. The new dark stain you're using will mask it.) Vacuum up the dust.

Sand the floor with the fine sanding belt to smooth out the wood. Vacuum the dust.

Brush dark wood stain over the floor with a paintbrush, working in sections of 4 to 6 square feet, starting at the furthest point from the doorway. Brush the stain on heavily, letting it puddle. Allow it to sit for one minute.

Wipe up the excess stain with rags. Continue until you cover the whole floor. Let the stain set for 12 hours.

Brush polyurethane floor gloss over the boards in a thin, even layer, starting again at the far side of the room and working with the direction of the boards.

Allow the polyurethane dry for eight hours. Use extra-fine sandpaper to de-gloss the surface, sanding it lightly by hand, just enough to dull the shine. Vacuum up the dust.

Apply a second coat of polyurethane. Allow it to dry for eight hours. Degloss it as before. Vacuum the dust. Add a third coat of polyurethane. Let it set for 24 hours.