- 1). 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.
- 2). 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.
- 3). Apply wood putty to fill any gouges, nail or screw head holes. Wait for the putty to dry, then re-prime the puttied areas.
- 4). Sand the entire surface with 220 grit sandpaper to remove wood fibers that may have raised when priming and create an ultra-smooth surface. Wipe off sawdust with a rag.
- 5). 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.
Source...