Once it has completely dried, sand edges smooth with 220-grit sandpaper. Fill any scratches on the face of the MDF with drywall compound as well, as any mars or scratches will be painfully obvious once painted.

How do I get a smooth finish on MDF?

Sand and Wipe MDF

MDF has a very smooth surface, but it tends to have rough, porous edges. For a smooth finish, you need to sand the edges of MDF down, but first, lightly sand the surface. A lightly sanded surface will give the MDF board a 'key' that the paint can cling to. Then wipe away any dust with a soft cloth.

Can you sand down MDF?

Sand the MDF after priming.

When sanding primer, use gentle pressure with your fine-grit sandpaper. When you are finished, the surface should be silky to the touch. Wipe dust from sanding away with a clean rag. The primer may lighten in color when sanding, but should still be visible.