Black stains on a hardwood floor usually means replacement. If the planks are square-edged, removal with a hammer and chisel followed by nailing down new replacement boards is as complex as it gets. If the damaged material is tongue and groove, use a circular saw to rip and remove about one-half inch of the center of the plank to be replaced. With the center of the damaged plank out of the way, pry the remaining pieces toward the center and away from their respective tongue and groove. To install a new piece, simply remove the lip below the groove, insert the new tongue into the old groove and hand-nail into place. Sanding and staining and a clear protective finish are all that is needed to complete the job. And that's the On The House tip for today.