Do MgSO4 boards have the same fire rating as MgCl2 boards?

 No, MgSO4 (sulfate-based) boards and MgCl2 (chloride-based) boards generally have the same high fire rating in their initial, dry state. The difference lies in the long-term stability of that rating in real-world, high-humidity applications.

Both types of boards are built primarily on Magnesium Oxide (MgO) cement, which is inherently non-combustible

 

1. Core Fire Rating is Identical

In laboratory tests, both MgSo4 and MgCl2 boards typically achieve the highest non-combustibility ratings:

• Non-Combustible Classification: Both are classified as Non-Combustible (e.g., Class A in ASTM E84 or A1 in EN 13501-1).
• Flame Spread and Smoke: They both usually achieve a Flame Spread Index of 0 and a Smoke Developed Index of 0 (or close to it) under ASTM E84 testing.
• Mechanism: Their fire resistance comes from the MGO mineral base and the water chemically bound within the cement. When heated, this bound water is released as steam, which helps cool the surface and block the spread of fire

2. Stability of the Fire Rating (MgSo4Advantage)

The major difference is how well each board maintains its fire rating when exposed to moisture over the lifetime of a building:

Feature	MgCl2​ Board (Chloride-Based)	MgSO4​ Board (Sulfate-Based)
Moisture Absorption	High. Chloride ions are highly hygroscopic (they attract and absorb moisture from the air).	Low. Sulfate is far less hygroscopic than chloride.
Corrosion Risk	High. Leaching chloride ions corrode steel studs and fasteners, compromising the wall assembly's structural integrity, which can lead to premature failure in a fire-rated assembly.	None. Non-corrosive to steel. The structural integrity is maintained.
Dimensional Stability	Poor in high humidity (prone to warping and swelling). This can cause gaps in fire-rated joints and compromise the assembly.	Excellent. Maintains dimensional stability, preserving the integrity of the fire-rated assembly.

 

Conclusion: While both boards have an excellent fire rating when new and dry, MgSo4boards are significantly more reliable for maintaining that fire rating in high-humidity or exterior conditions because they do not absorb moisture, corrode fasteners, or degrade the way MgCl2 boards do.

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Which type of MGO board is more suitable for high-humidity or exterior applications?

 Magnesium Sulfate (MgSO4) Board is unequivocally more suitable for high-humidity and exterior applications than Magnesium Chloride (MgCl2) Board.

The reason is the absence of high concentrations of chloride ions in the  (MgSO4) formulation, which eliminates the core problems associated with  (MgSO4)boards in wet environments:

1. Corrosion: (MgSO4) boards are non-corrosive to metal fasteners and steel frames, whereas (MgCl2) boards can leach corrosive chloride-salt water.
2. "Weeping" / Hygroscopy: (MgSO4) boards are less hygroscopic (do not readily absorb moisture from the air) and do not exhibit the "weeping" or "sweating" of saline water droplets common with (MgCl2) in high-humidity.
3. Dimensional Stability: (MgSO4)boards maintain better dimensional stability, resisting swelling and warping when exposed to moisture and temperature changes, making them much more reliable for exterior wall sheathing or bathroom use.

For any application involving moisture exposure, such as bathrooms, kitchens, basements, or exterior sheathing, (MgSO4) (sulfate-based) is the preferred and industry-recommended choice.

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Is MgSO4 board a structural sheathing material?

 The question of whether MgSO4 board is a structural sheathing material is complex and depends on the specific product and its code approval, but the general answer is Yes, specific, high-density MgSO4 formulations are engineered and approved for use as structural sheathing

Here is a breakdown:

1. Structural vs. Non-Structural

• Sheathing is a board or panel material covering the outer wall framing (studs).
• Structural Sheathing (like OSB or plywood) provides lateral load resistance (shear strength) to the building, helping it withstand forces like wind and earthquakes, and is required to have specific code-compliant strength values.
• Non-Structural Sheathing (like gypsum sheathing) primarily serves as a substrate for cladding, a weather barrier, or a fire-rated layer, but does not contribute to the building's racking strength.

2. MgSO4 Board Structural Performance

High-quality Magnesium Sulfate (MgSO4) boards are often specifically manufactured to meet the structural requirements for wall sheathing and subfloors. They generally offer:

• High Compressive and Flexural Strength: The dense, mineral composition reinforced with fiberglass mesh provides significant resistance to impact and bending forces.
• Shear Strength (Racking Resistance): Structural-grade MgSO4 products are tested to demonstrate shear values that allow them to be used as a direct replacement for OSB or plywood shear panels. They contribute to the structure's ability to resist forces that try to push the wall out of square.
• Dimensional Stability: The MgSO4 formulation is crucial here, as it provides the stability needed for exterior structural use. Unlike older MgCl2 boards, the sulfate-based boards do not degrade or lose strength due to moisture absorption or corrosion, ensuring long-term structural integrity.

3. Code and Approval is Key

Not all MGO boards are structural. To be used as code-compliant structural sheathing, the MgSO4 product must have a valid evaluation report (such as an ICC-ES report in the US) that specifically rates it for:

• Structural Sheathing: Defining the allowed stud spacing and fastener schedules to achieve the required shear wall ratings.
• Fire-Rated Assemblies: Often a major advantage, as MGO is non-combustible (Class A/A1 fire rating).

In short, when you see an MgSO4 board marketed as Structural Wall Sheathing or Structural Panel, it means the manufacturer has tested and certified it to meet the necessary building code performance criteria to provide shear strength. Always verify the specific product's official code report.

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Is the Mgo board safe and environmentally friendly?

 An MGO (Magnesium Oxide) board is generally considered a safe and environmentally friendly building material, often marketed as a greener alternative to traditional options like gypsum drywall and cement board.

Here is a detailed breakdown of its safety and environmental attributes, along with a crucial safety consideration：

Safety and Health Profile

MGO boards have several characteristics that make them a safe choice for building occupants and workers：

 Non-Toxic Composition: High-quality MGO boards are free from harmful substances commonly found in other materials, including:

• Formaldehyde
• Asbestos
• Volatile Organic Compounds (VOCs)
• Crystalline Silica

 Improved Indoor Air Quality: Since they do not off-gas VOCs or other toxic fumes, MGO boards contribute to a healthier indoor environment, which is beneficial for people with asthma or chemical sensitivities

 Superior Fire Resistance: MGO is naturally non-combustible. It has a high melting point and a very high fire rating (often a 0/0 rating on the ASTM E84/UL 723 Flame Spread and Smoke Developed Index). In a fire, it does not release toxic smoke.

 Mold and Pest Resistance: Being an inorganic, mineral-based material, MGO does not provide a food source for mold, mildew, fungus, or pests like termites and carpenter ants

Environmental Friendliness

MGO boards offer several significant environmental benefits:

• Low-Energy Manufacturing: The production of magnesium oxide typically requires less energy (sometimes 25% to 50% less) compared to materials like Portland cement or calcium hydroxide, leading to a lower manufacturing carbon footprint.
• CO₂ Sequestration: During the curing process, MGO boards actively capture and sequester carbon dioxide., which helps reduce greenhouse gas emissions.
• Abundant Raw Materials: Magnesium oxide is derived from magnesium, which is an abundant, naturally occurring mineral often sourced from seawater or brine pools.
• Recyclability: MGO boards are often described as fully recyclable or "nutritional waste." They can be crushed and repurposed into new boards or ground up and mixed into soil as a nutrient, minimizing landfill waste and promoting a circular economy.
• Durability and Energy Efficiency: Their resistance to moisture, mold, and pests results in a longer product lifespan, reducing the need for frequent replacement. Additionally, their good thermal insulation properties can help reduce a building's reliance on heating and cooling systems.

mportant Safety Consideration: The "Weeping" Issue

While generally very safe, there is one major caveat that consumers should be aware of, which relates to the board's binder:

• Magnesium Chloride Binder: Older or lower-quality MGO boards may use magnesium chloride as a binding agent. This compound is hygroscopic, meaning it absorbs moisture from the air, especially in high-humidity environments.
• Risk: This absorption can cause the board to "weep" or "sweat," releasing a salty, corrosive liquid (leachate). This liquid can cause severe corrosion of metal fasteners, steel studs, and aluminum components, potentially compromising the structural integrity of the assembly over time.
• Solution: Modern, high-quality MGO boards use a Magnesium Sulfate binder instead. This formulation is not hygroscopic and eliminates the risk of weeping and corrosion, making it a much safer and more reliable choice, particularly in humid or exterior applications.

In summary, to ensure you are using a safe and reliable product, it is critical to confirm that the MGO board you choose is a high-quality, modern, and Magnesium Sulfate-based formulation.

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How is the Mgo board fire resistance officially rated?

MGO Board Fire Resistance Official Ratings

Magnesium Oxide (MgO) boards are officially rated for fire resistance using various international standards that categorize their non-combustibility and the fire-resistance duration of the assembly they are part of.

Here are the key official ratings and standards for MgO boards:

Reaction to Fire Classification (Non-Combustibility)

This classification determines if the material itself will contribute fuel to a fire, and MgO boards consistently achieve the highest possible ratings.²

Standard	Rating/Classification	Description
European Standard	Euroclass A1	The highest classification, meaning the material is non-combustible and will not significantly contribute to a fire. This is often cited as the top level of fire safety. (Tested per EN 13501-1)
ASTM Standard (US)	ASTM E136 (Non-Combustible)	This is the standard test method for determining a material's non-combustibility when exposed to fire. MgO boards pass this test, confirming they do not burn.
ASTM Standard (US)	ASTM E84 / UL 723 Class A	This test measures surface burning characteristics, specifically Flame Spread Index (FSI) and Smoke Developed Index (SDI). MgO boards typically achieve a perfect 0/0 rating (Zero Flame Spread, Zero Smoke Developed), which is the best possible result and places them in the Class A (or Class 1) fire rating.

 

Fire Resistance Duration (Fire-Rated Assemblies)

This rating measures how long an entire building assembly (like a wall or ceiling) built with the material can withstand fire exposure, maintaining its integrity and insulation.³

Standard	Rating	Description
ASTM E119 / ANSI-UL 263	1-Hour, 2-Hour, (or up to) 4-Hour Ratings	This is the standard test for fire-resistance ratings of building construction and materials. It subjects complete wall or floor assemblies to a standardized fire. High-quality MgO board assemblies can achieve 1-hour, 2-hour, and even 4-hour fire ratings, often with less material or without the tapes and sealants required by traditional materials like gypsum.

 

Key Performance Highlights of MgO Boards

• Non-Combustible: MgO boards are fundamentally non-combustible.⁴
• High Temperature Resistance: They can withstand extreme temperatures, often up to  1400 ℉（800℃）or higher, without losing shape or strength.⁷
• Low Smoke and Toxicity: In fire tests, MgO boards show minimal to zero smoke and do not release toxic gases, which is a major factor in occupant safety.

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Is MGO board corrosive to metal fasteners and framing?

 

Yes, Magnesium Oxide (MgO) board can be corrosive to metal fasteners and framing, but the risk largely depends on the board's composition and the environmental conditions.

The primary factor is the presence of magnesium chloride as a binding agent, which is common in traditional or lower-quality MgO boards.

The Cause of Corrosion

The corrosion risk stems from the chloride content in the board:

• Chloride Content: Traditional MgO boards often use magnesium chloride  in their production.
• Moisture Absorption: Chloride salts are hygroscopic, meaning they readily absorb moisture from the air, especially in high humidity environments. This phenomenon is often called "weeping" or "sweating."
• Corrosive Leachate: When the chloride salts absorb moisture, they dissolve and form a highly corrosive, salty liquid (leachate) that migrates to the board's surface and contacts nearby metals.
• Metal Degradation: This chloride-rich liquid aggressively corrodes non-stainless steel fasteners (like galvanized steel) and metal framing, leading to rust, reduced structural integrity, and product failure

Non-Corrosive MGO Alternatives

To address this significant drawback, a newer, non-corrosive formulation has been developed:

MGO Board Type	Binding Agent	Corrosion Risk	Moisture Behavior
Traditional/Standard	Magnesium Chloride	High (especially in humid/wet conditions)	Highly hygroscopic, prone to "weeping" corrosive liquid.
Chloride-Free/Sulfate	Magnesium Sulfate	Very Low/None	Non-hygroscopic, stable, and eliminates the risk of chloride-induced corrosion.

 

Chloride-free MGO boards, which use (magnesium sulfate), are designed to be non-corrosive to metals, even in humid conditions

 

Best Practices for Metal Compatibility

If you are using or specifying any type of MGO board, you can mitigate the corrosion risk by taking precautions with the metal components:

1. Select Chloride-Free Boards: Prioritize boards manufactured using magnesium sulfate  to eliminate the source of the corrosive agent.
2. Use Corrosion-Resistant Fasteners: Always use high-grade, corrosion-resistant metals for fasteners and connecting metal parts:
   • Stainless Steel (304 or 316 grade) is highly recommended, especially in wet or exterior applications.
   • Coated Fasteners with epoxy, ceramic, or thick zinc-rich base layers are also used. Soft galvanized coatings should be avoided as the chloride can erode the zinc.
3. Ensure Proper Installation and Protection: Protect the boards from long-term saturation by using proper flashing, coatings, and membranes, as moisture is what activates the corrosive potential of any remaining chlorides.

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Will the MGO board "sweat" or leach fluid in humid conditions (Deliquescence)?

 Yes, some types of Magnesium Oxide (MgO) boards can "sweat" or leach fluid in humid conditions due to a process similar to deliquescence.

This phenomenon, often called "crying" or "sweating" boards, is a serious concern primarily associated with MgO boards that use magnesium chloride  as a binding agent, which forms magnesium oxychloride cement (MOC).

 

The Mechanism of Leaching/Sweating

The "sweating" is a direct result of the chemical composition of certain boards:

• Magnesium Chloride is Highly Hygroscopic: Magnesium chloride is a hygroscopic salt, meaning it readily absorbs and retains moisture from the air. The chemical composition of MOC cement is prone to this moisture absorption.
• Deliquescence: In environments with high relative humidity (RH), typically above 80-84% RH (the "weeping point" for some boards), the magnesium salts absorb so much atmospheric moisture that they dissolve in it, forming a concentrated salty water solution (leachate) that leaks out onto the board's surface.
• Corrosive Fluid: This leachate contains a high concentration of chloride ions, which makes the fluid extremely corrosive to adjacent materials, leading to the rapid rusting of metal fasteners, anchors, and structural elements like steel and aluminum.⁷ It can also cause moisture damage and mold growth in contacting timber elements.

Chloride-Free Alternatives

Due to the significant moisture-related issues and corrosion damage (famously seen in Denmark), manufacturers developed alternative formulations to mitigate this problem.

• Magnesium Sulfate Boards (MOS): Boards that use magnesium sulfate instead of magnesium chloride as a binder are generally much less hygroscopic and exhibit superior moisture resistance.
• Chloride-Free Boards: These alternative formulations are specifically designed to not absorb excessive moisture or leach corrosive chloride-containing fluid, thus preventing the "sweating" and related corrosion issues, even in high humidity environments.

In summary, the risk of "sweating" or deliquescence in an MgO board is directly dependent on its chemical formulation—specifically, the presence of magnesium chloride.

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