Magnesium Oxysulfate Board FAQ

MgO board, short for magnesium oxide board, is an inorganic sheet material used in building assemblies. The name covers more than one binder chemistry and many surface, density and reinforcement options, so two products sold as “MgO board” may perform differently. Sulfycor manufactures magnesium oxysulfate boards and supplies different series for sheathing, floors, ducts, SIP facings and finished interior walls. See the MgO board product range.

The cement binder is formed from reactive magnesium oxide, magnesium sulfate and water. Depending on the product series, the board also includes selected fillers, reinforcing materials and surface layers. Exact formulation, thickness, surface and reinforcement are controlled for the intended product—not assumed from the generic MgO name. Ask for the specification and technical documents that correspond to the board you are evaluating.

The main distinction is the magnesium salt used in the cement binder. Magnesium oxysulfate (MOS) uses magnesium sulfate, while magnesium oxychloride (MOC) uses magnesium chloride. Binder chemistry is important, but it is not the only selection factor: formulation, curing, reinforcement, surface, thickness and tested assembly also matter. Read our magnesium oxysulfate board overview for more context.

Sulfycor’s magnesium oxysulfate cement binder does not use magnesium chloride. We therefore describe these products as chloride-free MgO boards in relation to the binder system. Buyers should still review the exact product specification, surface and applicable test documents for the selected series and application rather than relying on one generic material label.

Specified MgO boards can be used in wall sheathing, subfloor and underlayment systems, interior wall finishes, structural insulated panel facings, modular-house walls and fire-rated ductwork assemblies. The board is one component of a system; framing, fasteners, joints, membranes, coatings and local code requirements also affect suitability. Use the MgO board applications hub to choose by project use.

Some MgO board products can be specified as exterior wall sheathing within a properly designed weather-managed assembly. “Exterior sheathing” does not mean the board should be treated as an exposed, waterproof finish. The wall design must address drainage, flashing, joints, coatings or cladding, fasteners and local environmental conditions. Review the wall sheathing application page before selecting a board.

Sulfycor supplies a sanded magnesium oxide board series for specified underlayment and structural subfloor assemblies. Required thickness, support spacing, fastening pattern, joint treatment, floor finish and loading criteria must be established for the complete floor system. Do not substitute a generic board based only on thickness. See the MgO subfloor application guidance.

Start with the assembly and desired surface. Non-woven finish boards are supplied for sheathing, ductwork and SIP facings; sanded boards are supplied for selected floor systems; and melamine- or HPL-faced decorative boards are supplied for finished interior and modular walls. Share the application, thickness, dimensions, quantity, destination and required standards so the relevant product can be matched before quotation.

MgO boards are inorganic and selected Sulfycor samples have been evaluated using applicable fire test methods. A fire classification or test result belongs to the specific product sample or assembly described in its report; it should not be applied automatically to every MgO board, thickness or wall system. Review the MgO board test evidence and confirm the report scope for your project.

There is no single fire rating for every MgO board. Reaction-to-fire classifications describe how a material contributes to fire, while fire-resistance ratings describe the tested performance of a complete wall, floor, ceiling or duct assembly over time. Board thickness, framing, insulation, joints and fasteners can all affect an assembly result. Tell us the required standard and construction detail so the relevant evidence can be checked.

MgO board should be described as water-resistant, not automatically waterproof. Suitability depends on the specific board and the complete assembly. Exterior and wet-area designs still require appropriate drainage, flashing, membranes, coatings, sealed penetrations and joint treatment. Prolonged standing water or immersion is outside normal sheathing and underlayment use unless a tested system explicitly permits it.

The inorganic board surface does not provide the same food source as paper-faced or wood-based materials. However, no board can compensate for leaks, trapped moisture or contamination on its surface. Mold performance depends on moisture control throughout the assembly, including drying potential, ventilation, membranes and maintenance. Treat mold resistance as one material characteristic, not a replacement for correct building-envelope design.

Sustainability cannot be established from the material name alone. It should be evaluated using verified information about raw materials, manufacturing energy, transport, service life, maintenance and end-of-life options for the specific product and project. Sulfycor does not use broad carbon or recyclability claims as a substitute for project evidence. Ask which technical and material documents are available for your evaluation.

Available thicknesses and sheet dimensions vary by product series, intended application and production arrangement. Standard and project-specific options can be discussed, but the right specification should be selected from support spacing, loading, fire or moisture requirements, surface finish and handling constraints—not size alone. Send the required thickness, length, width, edge detail and quantity for confirmation.

Density varies with formulation, reinforcement, surface and product series. A generic density copied from another supplier or article may not describe the board being quoted. Use the current product data sheet and tested sample identification when comparing boards. If weight, handling or structural performance is important, include those requirements in your enquiry so the appropriate specification can be reviewed.

It depends on the selected surface and assembly. Non-woven, sanded and decorative boards are not interchangeable, and some products have an intended face or finishing side. Follow the product marking, approved shop drawing and installation instructions supplied for the order. When the orientation is unclear, confirm it before fastening or applying primer, adhesive, coating or cladding.

Cutting method depends on board thickness, edge quality and project scale. Scoring and snapping may suit some thinner boards; power tools with an appropriate blade and dust extraction may be used for repeated or thicker cuts. Control dust, wear suitable personal protective equipment and support the sheet during cutting. Follow the MgO board installation guide and local site-safety requirements.

Use corrosion-resistant fasteners compatible with the board, framing material, exposure condition and required assembly. Fastener type, length, head, edge distance and spacing should come from the project specification or approved installation detail. Exterior, floor, SIP and duct applications can require different fastening systems. Confirm compatibility before substituting screws intended for drywall or another board material.

Joint gaps, reinforcement, fillers, primers, adhesives and coatings must be compatible with the selected board and final finish. The method differs between sheathing, floors, painted walls, tile systems and decorative panels. Allow for movement and environmental exposure as required by the assembly designer. Test unfamiliar finishing products on a sample and follow the current project installation instructions rather than a universal detail.

Yes. Samples and available technical documents can be reviewed before a bulk order. Because reports apply to identified samples, first share the intended application, board thickness, surface and required test standard. Sulfycor can then indicate which existing documents are relevant and whether further project-specific evaluation is needed. Start at the technical documents hub.

The standard minimum order is one 20GP container. The number of boards per container depends on thickness, sheet size, density, pallet arrangement and weight limits. Mixed specifications or special finishes may change production and packing feasibility, so the commercial quantity is confirmed after the product and dimensions are selected.

Please provide the application, board surface, thickness and dimensions, estimated quantity, destination country or port, required standards, preferred packaging and target schedule. For an assembly review, also share framing, support spacing, exposure conditions and intended finish. These details allow Sulfycor to recommend a relevant product and prepare a project-specific quotation instead of a misleading generic price.