Why MgO Boards Are Gaining Ground in Construction

Magnesium oxide (MgO) boards have become an increasingly popular alternative to traditional drywall and cement board in residential and commercial construction. They offer a compelling combination of fire resistance, moisture tolerance, dimensional stability, and structural rigidity. But like any building material, proper installation is critical to achieving the performance benefits the material promises.

This guide walks through the key steps and considerations for installing MgO boards on interior walls and ceilings.

Tools and Materials You'll Need

  • MgO boards (appropriate thickness for your application)
  • Carbide-tipped scoring knife or circular saw with a diamond/carbide blade
  • Self-tapping screws (corrosion-resistant, typically 25–45mm depending on board thickness)
  • Steel or timber stud framing
  • MgO-compatible jointing tape and compound (alkaline-resistant mesh tape)
  • Drill/driver
  • Straight edge and measuring tape
  • Safety goggles and dust mask

Step 1: Prepare the Framing

MgO boards can be fixed to either timber or metal stud framing. Stud spacing should be 400mm or 600mm centres, depending on the board thickness and load requirements. Ensure the framing is plumb, level, and free from moisture damage before proceeding.

Important: For ceiling applications, use 600mm centres maximum and choose a board thickness of at least 9mm to prevent sag over time.

Step 2: Cutting MgO Boards

MgO boards can be cut using two main methods:

  1. Score and snap: Use a carbide-tipped knife to score deeply along a straight edge, then snap the board cleanly. This is the preferred method for straight cuts as it minimises dust.
  2. Power cutting: Use a circular saw fitted with a diamond or carbide blade for curved or complex cuts. Always cut outdoors or in a well-ventilated area and wear a dust mask, as MgO dust can be an irritant.

Step 3: Fixing the Boards

Fix boards using corrosion-resistant self-tapping screws. Key rules for fixing:

  • Screws should be spaced 200–250mm apart along framing members
  • Keep screws at least 15mm from board edges and 50mm from corners to prevent cracking
  • Drive screws until the head sits just below the surface — do not overdrive
  • Stagger board joints so they don't align across adjacent rows

For wall applications, always install boards vertically where possible to reduce the number of horizontal joints that could allow moisture ingress.

Step 4: Jointing and Finishing

Unlike standard drywall, MgO boards require alkaline-resistant fibreglass mesh tape at joints — standard paper tape can degrade due to the slightly alkaline nature of MgO. Apply joint compound in thin coats, allowing each coat to fully cure before applying the next.

  1. Apply a thin bed coat of compound over the joint
  2. Embed alkaline-resistant mesh tape
  3. Apply two to three finishing coats, feathering edges wide
  4. Sand smooth once fully cured

Step 5: Priming and Decorating

MgO boards should be primed before painting. Use an alkali-resistant primer to prevent paint adhesion issues. After priming, virtually any paint system can be applied — emulsion, eggshell, or specialist coatings.

For tiled areas (such as wet rooms), use a polymer-modified tile adhesive rated for MgO substrates.

Common Installation Mistakes to Avoid

  • Using standard drywall screws: These corrode rapidly — always use corrosion-resistant fixings.
  • Skipping the alkaline-resistant tape: Standard tape will fail at joints within months.
  • Installing in direct contact with standing water: MgO boards are moisture-resistant, not waterproof — they need proper drainage detailing in wet areas.
  • Over-tightening screws: This fractures the board face and reduces holding strength.

Final Checklist Before Sign-Off

  • All joints taped and filled with compatible compound
  • Screw heads filled and sanded flush
  • Alkali-resistant primer applied
  • Adequate ventilation confirmed during curing phase