Hard wood floors were not in bad condition. Light sand with a 120 grit sand paper & a buffing machine.pass over surface enough times just to scuff the surface.All areas of floor must be completely free from trash and dust before adding clear polyurethane.
Second coat must be buffed using a 120 sanding screen.The best way to get up dust is to use a vacuum or a shop vac & a dust mop.Apply second coat of clear coat using a bucket or paint pan. Must use a lambs wool cloth and fine stain brush for edges. For third coat repeat the process. All coats need at least 6 hours or more to dry. fumes will be strong so ventilate properly with open windows and fans can also be used.