The prefinished hardwood floor is sealed with multiple coats of finish at the factory. The finish coats typically contain aluminum oxide, the second hardest substance next to diamond, to provide a hard-wearing protective finish. Unfinished flooring must be finished on site after installation takes place. Aluminum oxide cannot be used in the finish on site because the longer drying time causing the aluminum oxide particles to sink to the bottom of the finish. Site-finished floors usually are better at protecting against above floor moisture.