Why MgO Board Thickness Matters
Magnesium oxide boards come in a range of thicknesses — typically from 4mm up to 25mm or more. Selecting the wrong thickness can lead to structural weakness, poor fire performance, or unnecessary cost. Understanding what each thickness is designed for will help you specify the right product from the start.
Common MgO Board Thicknesses and Their Applications
| Thickness | Typical Use | Notes |
|---|---|---|
| 4–6mm | Ceiling linings, lightweight partitions | Best for non-load-bearing interior use only |
| 8–10mm | Interior wall cladding, wet areas | Good balance of weight and rigidity for bathrooms and kitchens |
| 12mm | Standard wall sheathing, fire-rated assemblies | Most versatile thickness; meets many fire code requirements |
| 15–18mm | Flooring underlayment, structural sheathing | Higher load capacity; suitable for floor systems |
| 20–25mm | Heavy-duty exterior, industrial applications | Maximum durability and impact resistance |
Interior Walls and Partitions
For standard interior partition walls, 10mm to 12mm boards are the most widely used. They offer sufficient rigidity when fastened to studs at standard 400mm or 600mm centres. In wet areas like bathrooms or laundry rooms, 10mm MgO board is preferred over drywall because of its inherent moisture resistance.
Ceilings
Ceiling applications require lighter boards to reduce dead load on the framing. 6mm to 9mm boards are typically used here. Always check the span rating of the specific product you're buying — span ratings vary between manufacturers, and an undersized board can sag over time.
Flooring Underlayment
When using MgO board as a floor underlayment or in a raised access floor system, you'll want at least 15mm to handle foot traffic and point loads. Some heavy-duty applications call for 18mm or 20mm. Look for boards with a stated compressive strength, not just a thickness specification.
Exterior Sheathing and Facade Systems
Exterior applications expose the board to weather cycling, UV, and impact. A minimum of 12mm is generally recommended, with 15mm preferred in climates with significant freeze-thaw cycles. Always confirm the board is rated for exterior use — not all MgO products are formulated for prolonged outdoor exposure.
Fire-Rated Assemblies
If you're designing a fire-rated wall or floor-ceiling assembly, the required thickness will be dictated by the tested assembly configuration. Most commonly, 12mm boards used in tested assemblies achieve 60-minute ratings, while stacked or double-layer applications can achieve higher ratings. Always reference the specific tested assembly rather than assuming thickness alone determines the fire rating.
Key Questions to Ask Before Buying
- What is the board's density? Higher density generally means better performance.
- Is the product certified for the intended application (interior, exterior, fire-rated)?
- What is the manufacturer's recommended fastener schedule for this thickness?
- Does the supplier offer technical data sheets with tested performance values?
Final Thoughts
Thickness is just one part of the specification puzzle. Always pair it with density, grade, and certification data. When in doubt, consult the manufacturer's technical support team or a structural engineer — especially for load-bearing or fire-rated applications.