Installing MgO Board on Walls: What You Need to Know First

Magnesium oxide board installs in a manner broadly similar to drywall and cement board, but there are important differences in cutting techniques, fastener selection, and finishing that you need to understand before starting. This guide covers interior stud-framed wall installations, with notes on exterior applications where they differ.

Tools and Materials Required

  • Circular saw with a carbide-tipped blade (score-and-snap works for thin boards)
  • Angle grinder with diamond blade (for curved or detailed cuts)
  • Corrosion-resistant screws (stainless steel or coated — standard drywall screws are not suitable)
  • Screw gun or drill/driver
  • Tape measure, pencil, chalk line
  • Safety glasses and dust mask (N95 minimum — MgO dust is an irritant)
  • MgO-compatible jointing compound or alkaline-resistant mesh tape and thinset
  • Level and square

Step 1: Plan Your Layout

Before touching the boards, plan the panel layout on paper. Key principles:

  • Stagger vertical joints so they don't align across adjacent rows — this improves structural integrity and reduces visible cracking at seams.
  • Ensure stud framing is at 400mm (16") or 600mm (24") centers, matching your board size for edge support.
  • Leave a 3–5mm expansion gap at all floor, ceiling, and corner transitions. MgO board has low thermal movement but moisture-driven dimensional change can occur.

Step 2: Cutting MgO Board

MgO board can be cut in two main ways depending on thickness:

  1. Score and snap (up to 10mm): Score deeply along a straight edge with a utility knife, then snap over a straight edge. Clean the broken edge with a rasp if needed.
  2. Power cutting (12mm and above): Use a circular saw with a fine-toothed carbide blade. Cut outdoors or with dust extraction — MgO dust is irritating to airways and eyes. Wear your PPE.

For curves and pipe holes, use an angle grinder with a diamond disc or a jigsaw with a bi-metal blade.

Step 3: Fastening Panels to Framing

This is where many installers make critical errors. Follow these guidelines:

  • Fastener type: Use stainless steel or hot-dip galvanised screws only. Standard zinc-plated drywall screws will corrode due to the alkaline chemistry of MgO — especially in humid environments.
  • Screw length: Minimum 25mm penetration into timber framing; for metal stud framing, use self-tapping screws rated for the metal gauge.
  • Spacing: Screws at 200mm centres around panel edges, 300mm in the field (interior of panel).
  • Edge distance: Keep screws at least 15mm from panel edges to prevent cracking.
  • Countersinking: Drive screws so the head sits just flush or slightly recessed — do not overdrive.

Step 4: Taping and Jointing Seams

MgO board seams require a compatible jointing system. There are two main approaches:

  1. Drywall-style finish: Use a flexible, MgO-compatible setting compound (not standard gypsum joint compound, which is pH-incompatible). Embed fibre tape into the first coat, then apply two additional coats, feathering each pass wider. Sand lightly when fully cured.
  2. Tile or render finish: Use alkali-resistant (AR) mesh tape with polymer-modified thinset mortar. This is the preferred approach for wet areas and tile installations.

Step 5: Priming and Finishing

MgO board is alkaline and requires a alkali-resistant primer before painting. Standard PVA primers are not suitable. Once primed, you can apply any standard interior paint. For exterior-facing boards, use a breathable, UV-stable exterior finish system.

Common Mistakes to Avoid

  • Using standard drywall screws (they'll corrode and stain the surface)
  • Skipping the expansion gap (leads to buckling or cracking at edges)
  • Using non-alkali-resistant joint tape (the tape will deteriorate)
  • Painting without an alkali-resistant primer (paint adhesion failure)
  • Storing boards flat on the ground without moisture protection before installation

Summary

MgO board installation is straightforward once you understand its material requirements. The key differences from drywall come down to fastener selection, jointing compound compatibility, and priming. Follow these steps and your installation will be durable, flat, and ready for any finish.