To get a glossy finish on a piece of medium-density fibreboard (MDF) you need to take your time to properly prepare the MDF. To do this, you need to paint, sand and polish the MDF to obtain a glossy finish. You can easily obtain a glossy finish by applying high-gloss paint. However, this typically does not last as the finish can dull over time or get scratched. Keeping a high-gloss finish requires using clear coat.
Sand the surface of the MDF with 200-grit sandpaper. You can do this by hand or by using an orbital sander. Avoid putting deep scratches into the MDF.
Wipe the surface of the MDF with a damp cloth to remove the dust and sanding residue.
Apply one coat of primer to the MDF with a paint brush. Allow one to two hours for the primer to dry and then sand it by using 400-grit sandpaper. Wipe the surface with a damp cloth. Repeat this step two more times.
Apply a third coat of primer, then sand it smooth with 800-grit sandpaper. Wipe the surface with a damp cloth.
Apply three light coats of paint (black or other solid colour) using spray paint. Allow at least 12 hours for the paint to dry. Sand the paint smooth with 800-grit sandpaper. Repeat this step two more times. Sand the final coat by using 1000-grit sandpaper.
Spray a coat of the clear coat over the surface of the paint and sand with 800-grit sandpaper. Repeat this step two more times and sand the final coat with 1000-grit sandpaper.
Wash the surface of the MDF with a clean cloth and allow it to dry. Apply a final clear coat and set the MDF aside for seven to 10 days to harden.
Polish the surface of the MDF with a buffing compound.