How to Seal MDF with a Rubberized Undercoating

Alexander Callos

MDF, or medium-density fiberboard, is a composite wood made from wood fibers that are glued together. It is used on interior applications including cabinets and shelves. MDF is also found on speaker boxes and molding. MDF is not able to withstand any moisture and will swell when it gets wet. This can lead to cracks and breaks in the boards. It can be sealed to help protect it from water. A rubberized undercoating is a simple and easy way to help protect MDF.

  1. Sand the MDF with 180-grit sandpaper. Move over the entire board in a circular motion to smooth out the surface. Continue until the whole area has been covered, making sure to sand the edges and sides. Wipe off dust particles with a clean rag.

  2. Spray a wet coat of primer over the entire piece of MDF. Spray from one side to the next, covering the whole surface with a thin coat. Allow it to air dry for 30 minutes.

  3. Sand the MDF with 280-grit sandpaper. Follow the procedure in step 1. Clean off the dust. Run your hand over the area to make sure it is smooth and there is no remaining residue from the sandpaper.

  4. Spray on the rubberized undercoating. Begin at one corner of the board and work side to side. Move up and down the MDF, covering the entire surface. Wait 30 minutes for the first coat to dry and add a second coat. Make sure to coat the edges of the MDF as well.

  5. Wait an hour for the second coat to dry. Inspect the MDF to make sure no spots were missed. Run your hands over the undercoating to make sure it is smooth and even.