Painting MDF Interior Doors

Sand the door with 150-grit sandpaper to remove dirt and provide a suitable surface to which paint will stick. MDF comes from the factory pre-sanded to 150-grit fineness. If your door is factory fresh and has a clean, even sheen, wipe it free of dust and skip the sanding.

Prime the door with a solvent-based primer such as oil or alcohol (white-tinted shellac) primer, using a 3-inch brush. Unfinished MDF absorbs water, so avoid water-based (latex) primers, which can raise MDF's papery fibers and prevent a smooth finish. Allow the primer to dry according to the manufacturer's instructions.

Sand the door with 220-grit sandpaper to remove dust and knock down any raised fibers. Vacuum away the dust or wipe clean the surface clean a barely dampened cloth.

Apply the top coat of paint with a brush. Load up the brush for even coverage and stroke the brush in the direction the grain would be if the door was genuine wood. MDF doors often have an embossed grain texture than can serve as a guide. If the door has a paneled appearance, paint the inside panels first, then the shorter horizontal rails. Finish by painting the vertical stiles and door edges. Allow the paint to dry overnight.

Add additional top coats if needed. Sand between coats with 220-grit sandpaper, but do not sand after the final coat. Allow each coat to dry overnight.