Medium Density Fiberboard, or MDF, is an engineered wood product that is used in cabinetry, moulding, shelving and furniture. It is made by binding together wood fibres with resin under pressure. MDF easily absorbs moisture, causing swelling, bending and delaminating. It must be primed and painted with the right products to seal out moisture and provide a provide a professional looking finish.
Sand the MDF with the 150 grit sandpaper. This will smooth out the rough sections of wood. Sand the edges of the board to remove splinters.
Apply an oil-based primer to the wood. Use a paintbrush for the end grain and inside corners. Use a roller for flat surfaces. Oil-based primers are better than water-based ones. The MDF will absorb too much of the moisture from water-based primers, leading to swelling. Oil-based primers seal better.
Apply wood putty to fill any gouges, nail or screw head holes. Wait for the putty to dry, then reprime the puttied areas.
Sand the entire surface with 220 grit sandpaper to remove wood fibres that may have raised when priming and create an ultra-smooth surface. Wipe off sawdust with a rag.
Paint the MDF. Use a clean paintbrush and roller to apply the paint. Apply multiple, thin coats of paint until the desired finished look is achieved. It may be necessary to lightly sand the surface between coats of paint.
Prime gouges, nail and screw holes before filling them with putty. Filling the holes prior to priming will draw the moisture from the putty into the wood, causing the putty to shrink and crack.
MDF dust particles are considered toxic. Work in a well-ventilated area and always wear a respirator-style face mask.