Why Magnesium Oxysulfide (MOS) Boards are Replacing Traditional MgO Boards in Fireproof Cladding?

 In modern commercial construction, data centers, and industrial facilities, structural fireproofing and wall cladding require materials that balance fire safety, mechanical strength, and long-term durability. While traditional Magnesium Oxychloride (MOC) boards—commonly known as standard Magnesium Oxide (MgO) boards—have long been popular, industry professionals are rapidly upgrading to Magnesium Oxysulfide (MOS) boards.

MOS technology solves the critical moisture absorption, weeping, and metal corrosion issues historically associated with traditional MgO boards, setting a new benchmark for fireproof cladding and structural subfloor panels.

Key Reasons MOS Boards are Replacing Traditional MgO Boards

1. Zero Halogenation & Moisture Resistance (No "Sweating")

Traditional MOC/MgO boards contain free chloride ions (Cl) that readily absorb ambient atmospheric moisture. In humid environments, this causes the boards to "weeping" or "sweat" (halogenation), leading to surface degradation and mold growth. MOS boards do not absorb moisture or weep, maintaining structural integrity even in high-humidity zones, underground spaces, or coastal regions.

2. Complete Protection Against Metal Corrosion

When traditional chloride-based MgO panels come into contact with steel studs, aluminum frames, or raised floor pedestals, free chloride ions accelerate galvanic corrosion, causing structural failure over time. MOS boards use a sulfate formulation that is 100% chloride-free, completely eliminating the risk of metal fastener corrosion.

3. Superior Dimensional Stability & Thermal Performance

Unlike calcium silicate or fiber cement panels that can warp under extreme heat, MOS boards offer exceptional dimensional stability. They exhibit minimal thermal expansion and contraction, preventing cracks in interior/exterior decorative wall cladding and floor panel joints.

4. A1-Class Fire Rating & Eco-Friendly Composition

MOS panels carry an A1 non-combustible fire rating. Under extreme temperatures, they do not burn, release toxic fumes, or generate heavy smoke. Furthermore, they are completely free of asbestos, formaldehyde, organic solvents, and heavy metals.

Side-by-Side Comparison: MOS vs. Traditional MgO (MOC) Boards

Feature / Property	Magnesium Oxysulfide (MOS) Board	Traditional MgO / MOC Board
Primary Salt Solution	Magnesium Sulfate (MgSO4)	Magnesium Chloride (MgCl2)
Free Chloride Content	0% (Chloride-Free)	High (Contains free Cl)
Moisture / Sweating Issue	None (No Halogenation)	High risk in humid environments
Metal Fastener Corrosion	Zero Corrosion Risk	High risk of rusting screws/frames
Fire Resistance Rating	A1 Class Non-Combustible	A1 Class Non-Combustible
Weathering & Durability	Excellent (Long-term stability)	Moderate (Degrades under moisture)
Ideal Applications	Cladding, Raised Floors, Cleanrooms	Dry interior partitions

 

 

Primary Applications of MOS Fireproof Boards

Fireproof Interior & Exterior Cladding: Used as decorative wall panels, interior partition boards, and curtain wall backing panels in high-rise commercial buildings, hospitals, and cleanrooms.

Raised Access Floor (RAF) Panels & Subfloors: Applied as high-density, fireproof core panels or subfloor boards in data centers and server rooms to support heavy equipment without risk of rusting underfloor pedestals.

 

Modular & Prefabricated Buildings: Replaces heavy cement boards and moisture-sensitive plywood, significantly lowering dead load while accelerating prefabricated assembly.

Fire-Rated Ceilings & Enclosures: Used for fire-resistant ductwork enclosures, shaft walls, and drop-ceiling systems requiring strict fire barrier compliance.

Selection and Installation Best Practices

Verify Sulfate Purity: Ensure the manufacturer specifies a true 100% sulfate-based (MgSO4) formulation with zero added chloride salts.

Density Selection: For decorative wall cladding, choose densities around 0.9g/cm3 - 1.1g/cm3. For heavy-duty subfloor or raised access floor applications, specify high-density MOS panels (1.25g/cm3).

Joint Treatment: Use specialized fire-rated, flexible joint compounds and alkali-resistant fiberglass tape at panel connections to accommodate structural settling and thermal movement.

 More information , please visit at www.hocre-board.com or send message by whatsapp +86 15001321220