When comparing Fiber Cement and MgO Sulfate (MOS) Board for facades, the choice often comes down to a trade-up between proven aesthetic durability (Fiber Cement) and superior technical safety/handling (MgO Sulfate)
While both are non-combustible alternatives to wood or plastic, they behave very differently in real-world exterior conditions.
Technical Comparison Table
| Feature | Fiber Cement (FC) | MgO Sulfate (MOS) |
| Primary Advantage | Aesthetic longevity & UV resistance | Fire safety & Moisture stability |
| Weight | Heavy (1,400+ kg/m3) | Lighter (1,000 – 1,100 kg/m3) |
| Moisture Response | Can absorb water; potential for “dark spots” | Highly stable; does not swell or warp |
| Fire Rating | Class A1/A2 (Up to 750℃) | Class A1 (Withstands >1,200℃) |
| Installation | Hard to cut; requires diamond blades | Easy to cut; “Score and Snap” or wood tools |
| Sustainability | High carbon footprint (Portland cement) | Low carbon footprint; recyclable |
Key Differences for Facade Applications
Fire Safety: The “Melt” vs. “Char” factor
- Fiber Cement: While non-combustible, fiber cement can crack or “spall” when exposed to extreme thermal shock.
- MgO Sulfate: It has a much higher melting point and better thermal insulation. In a rear-ventilated facade, MgO Sulfate acts as a superior thermal shield for the building’s insulation layer during a fire.
Moisture & “The Breathability Factor”
- Fiber Cement: Often contains cellulose (paper/wood) fibers. If the exterior coating fails, the board can absorb water, leading to localized swelling or mold over decades.
- MgO Sulfate: Being entirely inorganic, it is naturally mold-proof. Crucially, unlike “Chloride” MgO boards, the Sulfate version will not leach salt or “sweat” in humid coastal air, which protects your metal mounting system from rust.
Aesthetics and Finishing
- Fiber Cement: This is the winner for “ready-to-wear” facades. Brands like Equitone or James Hardie provide panels that are through-colored or textured to look like stone or wood.
- MgO Sulfate: Usually sold as a “raw” technical board. While it can be painted or rendered, it typically requires an additional coating step on-site unless you purchase pre-finished architectural MOS panels.
Which one should you choose?
- Choose Fiber Cement if: You want a finished, “out-of-the-box” decorative look with a 30-year proven track record for exterior colors and textures. It is the industry standard for high-end rainscreen aesthetics.
- Choose MgO Sulfate if: Your priority is structural safety and ease of work. It is ideal if the facade will be rendered (stuccoed) or if you are working in a region with extreme fire codes or very high humidity where traditional boards might fail or be too heavy for the frame.
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