Remove the nails from the floorboards by wedging a screwdriver under them and prying them up or using the back of a hammer to pull them out of the wood.
Wash the boards with a solution of warm water and liquid dish soap. Scrub the boards with a sponge to remove any dirt and debris then dry them with a towel to prevent excessive moisture absorption.
Adjust a planer so it is a 1/4-inch thinner than the thickness of the floorboards so you can remove the top layer of wood without significantly damaging the rest of the board.
Push each of the floorboards through the planer with a dowel rod. Avoid reaching your hand into the planer for safety purposes.
Readjust the planer by reducing the thickness by another 1/4-inch. Turn each of the floorboards over and run them through the planer again so the back of the boards also are prepared.
Cut the boards with a table saw, if necessary, to square them off. Trim the edges of any boards with irregular shapes. The boards are now ready to be adjusted, painted or cut, as needed, for any project.