Medium-density fiberboard (MDF) provides a strong, inexpensive wood alternative for your household projects. MDF is made from compressed wood fibres, which give the boards a distinctive texture. Unfortunately, this texture is not what most homeowners want on their finished product. Additionally, the fibrous nature of MDF absorbs paint if not properly prepared, making the paint highlight the texture rather than disguising it. To properly paint over MDF board texture, take the time to prepare your board properly.
Place a sheet of 120-grit sandpaper into a sanding block or powered sander. MDF contains formaldehyde, which is released when you sand and is hazardous to breathe.
Sand all surfaces of your MDF thoroughly, including the edges.
Wipe away all of your sanding dust with a rag. Keep wiping the surface with fresh rags until your rag comes away clean.
Apply a smooth coat of water-based primer over the entire MDF surface. Use brushes only for the corners and edges, then paint the main surfaces with a roller. Rollers with short nap (the fuzzy part of the roller pad) will give you the smoothest surface, but you need some length, such as 1/2 inch, to let the fibres work their way into the wood texture.
Sand the entire primed board after the primer thoroughly dries. Wipe the board down until it is free of dust after sanding.
Apply another coat of primer, paying special attention to the edges. Continue alternating priming and sanding until the board is as smooth as you want it, ending on a primer coat.
Apply one to two coats of latex paint over your primer to finish the board.
Experienced painters may achieve the best results by spraying MDF with the primer and paint, but brushes and rollers make applying paint easier for novices. Use only dry MDF for your products. Moisture can cause the wood fibres to swell and warp. Wear a respirator mask and work gloves.