Medium density fibre board, commonly known as MDF is a wood composite product with a highly consistent texture and a smooth surface. MDF panels are used for furniture construction and its consistency works well for prefab panelling and paint grade mouldings. MDF is primarily made up of wood particles, but is devoid of wood's natural oils, making it absorb paint more readily than natural hardwood.
Sand the main surface of the MDF with 150-grit sandpaper on a random orbit sander. It comes presanded, but a second pass is a good idea. Sand the edges as well, making two passes, since they come with the saw marks still on them. Use 100-grit sandpaper on the first pass and 150-grit sandpaper for the finish pass.
Prime the edges first with a soft bristle brush, working in long straight strokes, spreading the oil-based bonding primer as evenly as possible. Roll a coat of primer on the main surface with a medium nap roller. Spread the primer as evenly as possible to prevent runs and drips. Work the roller in a W pattern for even coverage. Allow the primer to dry for one hour. Apply a second coat using the same technique to seal the surface thoroughly. Allow the primer to dry thoroughly.
Apply two coats of semigloss paint to the surface of the MDF. Paint the edges first with a soft bristle brush, working in long straight strokes, spreading the paint as evenly as possible. Allow the paint to dry for the label recommended time before recoating. Use a short nap roller for a smooth coat on the main face of the board.
Apply the second coat of paint using the same technique. Spread the paint in a W pattern for adequate coverage. Roll the top coat on slowly to prevent bubbles in the finish. Allow the paint to cure thoroughly before handling the finished product.