How to Apply Minwax Polyurethane to MDF

Sand the piece of MDF with 120-grit sandpaper. Smooth out any imperfections in the board and cover the entire area in circular motions.

Vacuum up the surface with a small hand vacuum to remove any dust and debris that is left over from the sanding.

Apply the first coat of polyurethane over the MDF. Coat it on with a paintbrush using smooth short strokes. Work over the entire board until everything has been covered. Allow eight hours for the first coat to properly dry.

Sand over the first coat with 320-grit sandpaper. Go over the entire area to smooth out any imperfections or dust that remain from the first coat. Vacuum up the debris left over from the sandpaper once again. Apply a second coat of polyurethane in the exact same manner as the first coat and wait eight more hours for it to properly dry.

Sand down the second coat with the same 320-grit sandpaper and vacuum up the leftover debris. Apply a third and final coat for a complete finish. Allow eight hours for the final coat to dry before using the piece of MDF.