Magnesium oxide board ‘MgO board’ is a factory-made, non-insulating sheathing board product. It can be used for a number of applications including wall and ceiling linings, fascias, soffits, tile backing and underlayments. It is made of magnesium oxide, a type of mineral cement, and is commonly called simply ‘MgO’ due to its chemical composition of magnesium and oxygen . Think of MgO as a type of sheathing board–sort of like drywall or cement board–but with much-improved characteristics such as fire resistance, weatherability, strength, resistance to mold and mildew, and so on.
MgO is available in many forms, and for building construction comes in various thicknesses and sheet sizes. It also comes in various grades, such as smooth finishes, rough textures, and utility grades. It is white, beige or light gray in color, and has a hard sound when rapped with your knuckles–somewhat like portland cement board. There are dozens of companies that make MgO board, most of which are in Asia. There are several large producers, but most are small local manufacturers who serve a region.
MgO boards are harder than drywall, and are somewhat like the portland cement board used in bathtub enclosures. MgO is ‘worked’ in a manner like a combination of drywall and cement boards. It can be scored and snapped, although it is stronger than drywall and requires a bit more effort. It can be cut with a power saw, drilled-through and fastened like other similar boards.