Fibre Cement vs MgO Boards

Fibre Cement vs MgO Board: What’s the Difference?

In this blog, we’ll cover the fundamentals of fibre cement, before exploring the key similarities and differences between fibre cement boards and magnesium oxide (MgO) boards—two popular sheathing and lining materials used across modern construction.

What Is Fibre Cement?

Fibre cement is a composite building material manufactured from a blend of cement, mineral fillers (typically silica sand or limestone), water, and reinforcing cellulose fibres. This combination creates a board that offers an excellent balance of strength, dimensional stability, moisture resistance, and durability.

Because of these properties, fibre cement is widely used in applications such as:

• External wall sheathing
• Rainscreen cladding substrates
• Flooring systems
• Tile backer boards and wet rooms
• Soffits and fascias
• Fire-rated construction systems

One of fibre cement’s strongest technical advantages is its non-combustible nature, with many premium fibre cement boards achieving A1 classification to BS EN 13501-1, meaning they contribute no fuel load in a fire—the highest possible reaction-to-fire rating. BS EN 13501-1

Fibre Cement vs MgO: Key Differences

At first glance, fibre cement and MgO boards can appear similar—they are both rigid sheet materials used for sheathing, lining, and fire performance applications. However, there are some important differences.

1) Fire Classification

Fire performance is often where the two materials are compared most closely.

• Fibre Cement: Many high-quality fibre cement boards achieve A1 non-combustible classification.
• MgO Boards: Many MgO boards on the market are classified A2-s1,d0, which still represents excellent fire performance, but A2 is a lower classification than A1 and indicates limited combustibility rather than complete non-combustibility.

This is an important distinction for specifiers working on projects where true non-combustibility is required.

2) Moisture & Long-Term Stability

Fibre cement has a long, proven history in exposed and demanding environments.

Advantages include:

• Strong resistance to rot
• Resistance to insect attack
• Good dimensional stability
• Excellent weather durability
• Proven long-term external performance

MgO boards can also perform well, but performance can vary significantly depending on board formulation, chloride content, manufacturing quality, and environmental exposure. Historically, some lower-grade MgO products have experienced issues such as:

• Moisture absorption
• Surface sweating/efflorescence
• Corrosion risk to metal fixings (in chloride-rich formulations)
• Dimensional instability in humid conditions

Not all MgO products suffer from these issues—but specification quality matters heavily.

3) Strength & Rigidity

Fibre cement offers:

• High compressive strength
• Excellent rigidity
• Strong screw pull-out performance
• Reliable structural backing for façade systems

This makes it well suited to demanding construction applications where board integrity is critical.

4) Design Flexibility

Fibre cement is available in a wide range of:

• Thicknesses
• Textures
• Surface finishes
• Factory coatings
• Application-specific board grades

This makes it suitable for everything from concealed sheathing to decorative façade finishes.

Benefits of Fibre Cement

Durability

Fibre cement is exceptionally durable and resistant to:

• Rot
• Corrosion
• Moisture damage
• Pest attack
• Freeze-thaw cycles

Fire Performance

Many fibre cement products achieve A1 classification, offering genuine non-combustible performance.

Versatility

Suitable for:

• External sheathing
• Internal lining
• Flooring
• Tile backing
• Ceiling systems
• Façade systems

Low Maintenance

Fibre cement is stable, reliable, and requires minimal upkeep over its service life.

Are There Any Downsides?

Like any building material, fibre cement isn’t perfect.

Weight

Fibre cement is heavier than some lightweight alternatives.

For example, a board with a density of 1,350kg/m³ means a 1000mm × 1000mm × 10mm panel weighs approximately 13.5kg, which can affect handling and installation logistics.

Installation

Cutting and fitting fibre cement often requires:

• Appropriate tooling
• Dust control measures
• Correct fixing methods
• Installer experience

Quality Variation

Not all fibre cement is manufactured to the same standard.

Board quality can vary considerably across the market, which is why selecting a proven, specification-grade product is essential. Speaking with a technical specialist before specifying material can help ensure the board selected is appropriate for the application.



Final Thoughts

Both fibre cement and MgO boards have their place in modern construction. However, where projects demand:

✔ Proven long-term durability
✔ Moisture resistance
✔ Dimensional stability
✔ True A1 non-combustible performance
✔ Reliable structural strength

Fibre cement remains one of the most trusted and technically robust solutions available.

For guidance on selecting the right fibre cement board for your application, speak to the CemBloc team.