Before You Begin: Tools and Materials

Installing MgO board is similar in many ways to hanging drywall or cement board, but there are key differences in cutting, fastening, and finishing. Gather the following before starting:

  • MgO boards (appropriate thickness for your application)
  • Carbide-tipped scoring knife or circular saw with a carbide blade
  • Self-tapping screws rated for MgO board (typically corrosion-resistant)
  • Alkaline-resistant fiberglass mesh tape
  • MgO-compatible joint compound or polymer-modified mortar
  • Drill/driver with torque control
  • Level, tape measure, and chalk line
  • Safety glasses and dust mask (N95 or better)

Step 1: Prepare the Framing

MgO board can be fastened to steel or wood studs. For interior walls, standard 16" or 24" on-center framing applies. For exterior applications, ensure framing is plumb and true — MgO board will telegraph any irregularities in the substrate.

Important: Maintain a minimum 1/8" (3 mm) gap at floor level and perimeter edges to allow for slight movement and prevent moisture wicking from concrete slabs.

Step 2: Cut the Boards to Size

MgO board can be cut using two methods:

  1. Score and snap — Use a carbide-tipped knife to score the board at least halfway through, then snap cleanly over a straight edge. This is the preferred method for straight cuts and produces minimal dust.
  2. Power cutting — Use a circular saw with a carbide or diamond blade for complex cuts, notches, and curves. Always cut outdoors or in a well-ventilated area and wear respiratory protection.

Step 3: Fasten the Boards

Use corrosion-resistant, self-tapping screws specifically rated for use with MgO board. Avoid standard drywall screws — they can corrode due to the chloride content in some MgO formulations.

  • Screw spacing: 8" (200 mm) on center at edges, 12" (300 mm) in the field
  • Edge distance: minimum 5/8" (16 mm) from the board edge
  • Drive screws flush — do not overdrive, as this can fracture the board surface
  • Begin fastening from the center of each board and work outward

Step 4: Tape and Joint the Seams

Proper jointing is critical for a durable, water-resistant finish:

  1. Apply a thin bed of MgO-compatible polymer mortar or joint compound over each seam.
  2. Embed alkaline-resistant fiberglass mesh tape into the wet compound.
  3. Apply a second coat, feathering edges at least 6" on each side of the seam.
  4. Allow to dry fully (typically 24 hours), then lightly sand smooth.
  5. Fill screw dimples with joint compound and sand flush.

Do not use standard paper drywall tape — it will not bond reliably to MgO surfaces and can fail in humid environments.

Step 5: Finishing Options

MgO board accepts a wide variety of finishes:

  • Paint — Apply a quality primer first; MgO surfaces are slightly alkaline, so use an alkali-resistant primer before topcoating.
  • Tile — Apply tile directly using polymer-modified thinset mortar. MgO board is an excellent tile backer in wet areas.
  • Skim coat — A thin skim coat of finish plaster can be applied for a smooth painted wall surface.
  • Texture — Standard spray textures adhere well over properly primed MgO surfaces.

Common Installation Mistakes to Avoid

  • Using standard drywall screws that will rust over time
  • Skipping the perimeter gap, leading to board swelling and buckling
  • Over-driving screws and cracking the board face
  • Using non-alkaline-resistant tape that degrades behind tiles
  • Applying finish coats before seams are fully cured

Following these steps will result in a durable, high-performance wall assembly that maximizes the fire and moisture resistance MgO board is engineered to provide.