A valued characteristic of unfinished hardwood floors, however, lies in the uniformity of the finish. Pre-finished floors are by definition on a board by board basis, and the finish which seals the board does not seal the minute spaces between individual hardwood planks in the same way. With an unfinished floor, the finish is added over the surface of a hardwood floor as a whole after the boards have been installed. This offers a generally more uniform finish and a somewhat greater moisture-proof seal. Many subcontractors choose to install unfinished hardwood floors for these reasons.