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MgO Sulfate board (Magnesium Oxysulfate / MOS) is considered a “second-generation” advancement over the traditional Chloride MgO board (Magnesium Oxychloride / MOC).

The primary reason it is “better” is that it solves the two most significant failures of the original technology: metal corrosion and “sweating” (leaching).

1. No “Sweating” or Leaching (Non-Hygroscopic)

Traditional Chloride boards use Magnesium Chloride (MgCl2), which is highly hygroscopic—meaning it naturally attracts moisture from the air.

• The Problem: In humid environments, Chloride boards absorb so much water that droplets of salty brine form on the surface. This is known as “sweating,” “crying,” or “weeping.” This moisture ruins paint, causes wallpaper to peel, and encourages mold on adjacent materials.
• The Sulfate Advantage: Sulfate boards use Magnesium Sulfate (MgSO4), which is not hygroscopic. Even in 90% humidity, the board remains dry and stable because it does not pull moisture from the atmosphere

2. Zero Corrosion to Metal Fasteners

The biggest disaster associated with traditional MgO boards is the destruction of building structures.

• The Problem: The chloride ions in MOC boards are chemically aggressive. When combined with “sweating” moisture, they form a corrosive brine that eats through galvanized steel studs, copper pipes, and aluminum frames within a few years.
• The Sulfate Advantage: MgO Sulfate boards are 100% chloride-free. They are chemically inert toward metals, meaning you can safely use standard galvanized screws and light-gauge steel framing without risk of structural failure.

3. Superior Dimensional Stability

Sulfate boards handle temperature and moisture changes more gracefully than chloride boards.

• Moisture Resistance: Tests show that Sulfate boards absorb significantly less water (up to 37% less in high humidity) than chloride boards.
• Anti-Warping: Because they don’t soak up water, they are far less likely to swell, warp, or delaminate over time, making them a much more reliable substrate for tiling and high-end finishes.

• Summary Comparison Table