MDF, or medium density fiberboard, is raw building stock made from wood fibres compressed with adhesive. MDF has gained popularity as a building material among do-it-yourselfers because it is easy to work with and affordable. According to Ergo In Demand, a manufacturer of office furniture, MDF is also environmentally friendly, reducing waste from other wood products. The smooth surface of MDF readily accepts paints, stains and varnishes, but the exposed edges must be sealed prior to finishing to lend an even look to the finish.
Sand the exposed edge of the MDF lightly with 120-grit sandpaper to smooth any rough spots. Wipe down the edge with a tack cloth to remove any sanding dust.
Scoop a small amount of joint compound onto the putty knife and apply a thin layer down the length of the exposed edge. Holding the putty knife at a 45-degree angle, run the knife in one motion down the edge of the MDF, applying slight pressure to create flex in the blade. This leaves a smooth coat of joint compound and removes any excess.
Allow the joint compound to dry fully, several hours to overnight depending on how thickly it was applied.
Sand the dry joint compound smooth with 120-grit sandpaper. Wipe the MDF with a tack cloth to remove dust from the joint compound.
Wear a mask when sanding to prevent inhalation of fine particles.