Why MgO Board Is Ideal for Bathroom Renovations
Bathrooms are among the most demanding environments in a home — high humidity, steam, occasional splashing, and temperature swings put wall linings under real stress. Traditional plasterboard and even "moisture-resistant" drywall can swell, delaminate, and grow mould behind tiles when moisture finds a way in. MgO board's mineral composition makes it genuinely moisture-resistant and mould-resistant, giving tiled surfaces a durable, long-lasting substrate.
What You'll Need for This Project
- MgO board — 10mm or 12mm recommended for bathroom walls
- Corrosion-resistant screws (stainless steel, 35mm for 12mm board into timber framing)
- Alkali-resistant fibreglass mesh tape
- MgO-compatible jointing compound (for any joints you need to fill)
- Waterproof membrane or tanking system (for shower enclosures)
- Tile adhesive rated for wet areas
- Tiles of your choice
- Grout and grout sealant
- Safety glasses, dust mask, measuring tape, pencil, scoring knife or saw
Step 1: Remove Existing Wall Linings
Strip back to the bare framing. This is the chance to check for any existing mould, damaged framing members, or old plumbing that needs attention. Address all of this before you put a new lining up — you do not want to seal problems behind fresh boards.
Check that all framing is plumb and solid. Hammer in any popped nails and fix any loose noggins. If you're working around a shower, confirm the waterproofing membrane location relative to the framing.
Step 2: Cut and Fix MgO Board
Measure each wall section carefully. Cut MgO board to size using a scoring knife (score deeply on both sides for a clean snap) or a fine-tooth saw blade for precise cuts around windows, niches, or outlets.
- Fix boards with the long edge vertical where possible.
- Use stainless steel screws at 200mm centres along edges and 300mm in the field.
- Keep screw heads just flush — overdriving cracks the face and reduces holding strength.
- Leave a 3–5mm gap at floor level (expansion and drainage clearance).
- Stagger joints between rows so vertical seams don't align.
Step 3: Tape Joints (If Tiling Over)
If you're tiling directly over the MgO board (as opposed to painting it), you don't need to skim the entire surface. However, tape all joints with alkali-resistant fibreglass mesh tape and bed the tape into a thin layer of tile adhesive or MgO-compatible compound. This prevents any differential movement at joints from cracking tiles above.
Step 4: Apply Waterproof Membrane in Wet Zones
In the shower enclosure and around the bath, apply a liquid waterproof membrane over the MgO board surface before tiling. Although MgO board is moisture-resistant, it is not inherently waterproof under sustained immersion. A properly applied tanking membrane prevents water from reaching the framing and provides the true waterproof layer.
Apply the membrane in two coats according to the manufacturer's instructions, paying extra attention to corners, screw heads, and joints — these are the highest-risk areas for water infiltration.
Step 5: Tile Over the MgO Board
MgO board provides an excellent tiling substrate. Use a polymer-modified, wet-area tile adhesive. Apply the adhesive to the board using a notched trowel appropriate for your tile size, back-butter larger tiles, and set them according to your layout.
- Allow the adhesive to cure fully before grouting — typically 24 hours minimum.
- Use a waterproof grout or seal standard grout after curing.
- Apply a quality grout sealant to all grout lines in the shower for maximum longevity.
Alternative: Painted MgO Board for Lower-Moisture Areas
For bathroom walls outside the wet zone (e.g., the wall opposite the shower), you can leave MgO board unlined and simply prime and paint it. Use an alkali-resistant primer first, then any quality bathroom-grade paint. This gives a clean, durable finish with excellent mould resistance.
Project Tips for Best Results
- Always prime MgO board before painting — skip this and paint adhesion will fail.
- Don't mix fastener types — stainless steel throughout prevents staining and corrosion.
- Seal cut edges of boards in wet areas with waterproof membrane or adhesive before tiling.
- Plan tile layout before fixing boards to ensure joints don't fall on board seams where possible.
Done well, an MgO-boarded bathroom will outperform conventional linings for years — resisting moisture, mould, and wear in one of the home's hardest-working spaces.