How to Install Magnesium Oxide Board for Sub-Flooring | 7 Steps

Installing a durable and moisture-resistant subfloor is essential for any building project. Magnesium oxide (MgO) board offers a modern alternative to traditional sub-flooring materials, boasting superior fire resistance, strength, and environmental benefits. This guide walks you through everything you need to know about installing MgO board for sub-flooring applications.

---

Magnesium oxide board is a type of non-combustible, cement-like panel made from magnesium oxide (MgO), magnesium chloride, and other reinforcing materials such as perlite, fiberglass mesh, or wood flour. It’s known for its strength, fire resistance, mold resistance, and versatility.

MgO board is increasingly used as a sub-flooring material due to its ability to withstand moisture, resist warping, and provide a solid, long-lasting surface under tile, laminate, or other floor finishes.

---

1. Fire Resistance: MgO board is non-combustible and can withstand high temperatures, making it ideal for areas requiring fire-rated construction.
2. Water Resistance: Unlike plywood or OSB, MgO board doesn’t swell or degrade when exposed to moisture.
3. Mold & Mildew Resistance: Its inorganic composition makes it resistant to mold, mildew, and insects.
4. High Strength: It supports heavy loads and provides a strong base for flooring finishes.
5. Environmentally Friendly: MgO board is made from natural materials and is often recyclable.

---

• Magnesium Oxide (MgO) Boards
• Measuring tape
• T-square or straight edge
• Utility knife or circular saw with a diamond blade
• Construction adhesive (optional)
• Corrosion-resistant screws
• Screw gun or drill
• Joint tape (alkali-resistant fiberglass mesh)
• Joint compound or skim coat (if required)
• Safety gear: gloves, safety goggles, dust mask

---

• Ensure the substrate is clean, dry, and level.
• Remove any loose debris, dust, or high spots.

• Let MgO boards sit in the installation area for 24–48 hours to adjust to ambient conditions.

• If installing over wood joists or in a wet area, consider a waterproof membrane or vapor barrier underneath the MgO board.

---

• Measure the area to calculate how many boards you’ll need.
• Plan the layout to minimize cutting and ensure proper board staggering.

• Use a circular saw with a carbide or diamond blade to cut MgO boards.
• Wear appropriate safety gear, as cutting produces fine dust.

• Lay the boards on the floor to check the fit.
• Leave a 3–5 mm expansion gap between panels and a 5–10 mm gap around the perimeter.

• For added bond and soundproofing, apply construction adhesive to the back of each board or directly on the floor.

• Use corrosion-resistant screws every 6–8 inches along the edges and every 8–12 inches in the field.
• Drive screws flush with the board surface without over-tightening.

• Tape all joints with alkali-resistant mesh tape.
• For tiled finishes, apply a skim coat or thinset mortar over joints for a level surface.

• Remove dust and debris from the surface.
• Inspect all fasteners and joints for stability and flushness.

---

When choosing the right sub-flooring for a project, it’s crucial to understand how magnesium oxide (MgO) board compares to other commonly used materials like plywood, oriented strand board (OSB), and cement board. Each material has its own strengths and limitations. However, for builders, contractors, and homeowners concerned with fire safety, moisture resistance, and long-term performance, MgO board often stands out. Below is a detailed comparison.

Plywood is a combustible material made from wood veneers. When exposed to fire, it can ignite easily and contribute to flame spread. In contrast, MgO board is non-combustible and can resist fire for up to 2 hours depending on its thickness and composition. For those learning how to install magnesium oxide board, one of the top benefits is knowing that you’re using a material that contributes to overall building fire safety.

Plywood absorbs moisture readily and is prone to swelling, warping, and delamination, especially when used in humid or wet environments. Even pressure-treated plywood has limitations. MgO board, on the other hand, is inherently water-resistant. It maintains structural integrity even after prolonged exposure to moisture, making it ideal for sub-flooring in bathrooms, kitchens, basements, and laundry areas.

Wood-based products like plywood can become breeding grounds for mold and mildew when they absorb water. Mold not only deteriorates materials but also poses health risks. MgO board is inorganic and does not support mold growth. This feature is particularly important when considering how to install magnesium oxide board in environments prone to dampness or poor ventilation.

OSB is made by compressing layers of wood strands with adhesive resins. While it’s often chosen for its affordability and uniform structure, OSB is susceptible to edge swelling, rotting, and general deterioration over time—especially in areas with fluctuating humidity. MgO board, being mineral-based, resists rotting, insect infestation, and decay. When durability is a concern, MgO clearly outperforms OSB.

Humidity and temperature changes can cause OSB to warp, twist, or expand, compromising the evenness of the subfloor. MgO board exhibits superior dimensional stability—it remains flat and rigid even in harsh environmental conditions. This makes a huge difference when applying final floor finishes like tile, laminate, or vinyl, as uneven substrates can lead to costly repairs.

OSB is generally easier to fasten using nails and standard tools, which may be attractive to DIYers. However, when installed correctly with corrosion-resistant screws, MgO board delivers far superior performance, especially over time. Learning how to install magnesium oxide board correctly includes mastering screw spacing, edge sealing, and joint taping—tasks that yield better long-term results than basic OSB nailing.

Cement board is another non-combustible material often used for tile backer applications and wet environments. However, it is significantly heavier than MgO board, which makes transport, handling, and cutting more labor-intensive. MgO board is lightweight and easier to score, cut, and maneuver during installation, making it more user-friendly for both professionals and homeowners.

Both MgO and cement board create dust when cut. However, MgO often produces finer, less hazardous dust particles compared to the coarser silica-laden dust from cement boards. This is an important safety consideration during installation. When learning how to install magnesium oxide board, it’s still critical to wear protective gear such as masks and goggles, but overall, the cutting process is cleaner and safer.

Cement boards are rigid and prone to cracking if bent or stressed improperly during installation. MgO board offers a slight degree of flexibility while still maintaining high tensile strength. This flexibility helps MgO boards resist cracking from movement or vibration in the substructure, which is especially valuable in multi-story buildings and mobile structures like modular homes or RVs.

Feature	Plywood	OSB	Cement Board	MgO Board
Fire Resistance	Combustible	Combustible	Non-combustible	Non-combustible (up to 2 hrs)
Water Resistance	Swells, delaminates	Swells, deteriorates	Good	Excellent
Mold Resistance	Prone to mold	Can mold	Mold-resistant	Mold-proof
Durability	Moderate	Moderate	High	Very High
Ease of Cutting	Easy	Easy	Difficult	Moderate
Weight	Light	Moderate	Heavy	Light
Dimensional Stability	Low	Low	Medium	High
Installation Method	Nails/Screws	Nails/Screws	Screws + Backer Mesh	Screws + Tape + Sealant

When it comes to performance, MgO board consistently outperforms plywood, OSB, and even cement board in critical areas such as fire resistance, moisture protection, and durability. While each material has its place in construction, MgO board offers a versatile and reliable solution for sub-flooring needs across both residential and commercial applications.

Understanding how to install magnesium oxide board effectively gives you an edge in creating a subfloor that is built to last. With proper installation techniques, MgO board ensures safety, longevity, and minimal maintenance, making it a superior choice for modern building projects.

---

Failing to leave a 3–5mm gap between boards and a 5–10mm gap around the perimeter can result in buckling or cracking due to thermal expansion.

Standard drywall screws can corrode or lose grip. Always use corrosion-resistant screws designed for cementitious materials.

Not taping or sealing joints can lead to water penetration or joint movement under load.

MgO dust may irritate the respiratory system. Always cut with a mask and in a well-ventilated space.

Installing on an uneven or damp substrate will cause poor adhesion and eventual failure. Always level and dry the surface before installation.

---

• Bathrooms and Laundry Rooms: High humidity areas benefit from MgO’s mold resistance.
• Basements: Moisture-prone basements stay dry and odor-free with MgO subfloors.
• Kitchens: Fire resistance is an added bonus in high-traffic cooking areas.

• Hospitals and Clinics: MgO’s hygienic properties and fire safety make it ideal.
• Schools and Dormitories: Durable under high foot traffic and long-lasting.
• Restaurants and Cafeterias: Easy to maintain and resistant to spills and heat.

• Warehouses and Cold Storage: Withstands temperature changes and moisture.
• Pool Houses and Saunas: Excellent dimensional stability and no mold growth.

---

Yes. MgO board provides a rigid, stable base that is ideal for tile installations. Use a polymer-modified thinset and ensure joints are properly taped.

Yes. MgO has excellent thermal conductivity and is stable under varying temperatures, making it compatible with radiant heat systems.

Not always. If used in dry indoor areas, sealing may not be required. In wet or high-humidity environments, a primer or waterproof membrane is recommended.

Yes. After ensuring joints are taped and surface is flat, you can install laminate, vinyl, engineered wood, or tile directly on top.

When properly installed and maintained, MgO boards can last over 50 years without significant degradation.

---

1. Avoid Excessive Moisture Exposure: While MgO is moisture-resistant, prevent long-term standing water.
2. Re-seal if Needed: In wet zones, re-seal the joints or surface every 5–10 years.
3. Check Fasteners Annually: Make sure screws remain tight and no movement occurs.
4. Protect During Renovation: If you’re working on other parts of the building, cover the subfloor to avoid damage.

---

Environmental Benefits of Using MgO Board

Magnesium oxide is derived from abundant natural minerals such as magnesite or seawater-based brines. Unlike wood-based products like plywood or OSB, MgO boards do not contribute to deforestation.

Compared to cement-based or gypsum-based boards, MgO requires significantly less energy to manufacture. Its production process emits fewer greenhouse gases and has a lower carbon footprint overall.

MgO boards do not contain formaldehyde, asbestos, or other harmful chemicals commonly found in composite panels or insulation materials. This makes them safer for indoor air quality and human health.

MgO board waste can be ground and reused as a component in future MgO board production, reducing landfill use and promoting circular building material practices.

Volatile Organic Compounds (VOCs) can cause health issues and are present in many conventional subfloor materials. MgO boards are VOC-free, contributing to healthier indoor environments.

---

Use your measuring tape to determine the size of each floor section. Snap chalk lines across the substrate to map out where each MgO board will go. This helps you maintain straight, aligned rows during installation.

Place the MgO board flat on a sawhorse or workbench. Using a circular saw equipped with a carbide-tipped or diamond blade, cut the board carefully along your marked lines. Always wear a dust mask and goggles.

Before applying adhesive or fasteners, lay the boards down in their final positions to confirm proper fit. Leave 3–5mm between adjacent boards and a 5–10mm expansion gap along the walls.

For added soundproofing and stability, apply a serpentine bead of construction adhesive to the subfloor or joists using a caulking gun. Don’t over-apply—too much glue can cause bumps or improper seating.

Secure each board using corrosion-resistant screws, spaced approximately every 6–8 inches around the perimeter and 8–12 inches in the field. Start from one corner and work outward, walking across the board carefully to prevent flexing.

Once all boards are secured, tape each joint with alkali-resistant fiberglass mesh tape. If required, skim a thin layer of joint compound over the tape using a wide drywall knife.

Use a long straight edge to check for any uneven spots. Make sure no screw heads are protruding and that all boards are seated firmly. Clean the surface with a shop vac before proceeding to finish flooring.

---

One person can pre-cut and layout boards while the other fastens them. This assembly-line approach increases productivity, especially in large spaces.

In tight or curved sections, such as around bathtubs or stairwells, pre-drilling screw holes can prevent board cracking and speed up fastening.

Use black or coated screws to visually confirm which areas have been fastened already. It helps avoid missed spots during fast-paced installations.

When pre-cutting multiple boards, label each piece based on its location (e.g., “A1”, “B3”) using a pencil or chalk. It reduces confusion during dry fitting.

Allow boards to acclimate to room temperature and humidity for 24–48 hours before installation. This minimizes expansion and contraction post-installation.

For large or commercial areas, use a laser level to check substrate flatness before starting. Uneven substrates lead to creaking or hollow sounds under finished floors.

---

Installing magnesium oxide board as a sub-flooring material is not just a construction choice—it’s a forward-thinking investment in the safety, durability, and long-term performance of your building project. With its impressive fire resistance, moisture protection, mold resistance, and structural integrity, MgO board consistently outperforms many conventional sub-flooring materials in nearly every critical metric.

By taking the time to learn how to install magnesium oxide board correctly, you’re ensuring that your floor system remains stable and secure for years to come. Proper installation—combined with careful preparation and attention to detail—helps avoid common mistakes and maximizes the material’s unique benefits. Whether you’re working on a new residential development, a commercial facility, or even a modular construction project, MgO board offers a superior foundation that supports all types of floor finishes—from tile and hardwood to vinyl and carpet.

In an era where sustainable and fire-safe building materials are becoming increasingly important, magnesium oxide board is not only a smart choice—it’s a responsible one. Its eco-friendly composition, longevity, and performance under extreme conditions make it an ideal solution for modern construction challenges.

If you’re a builder, contractor, architect, or distributor looking to source premium MgO boards or simply want more expert advice on how to install magnesium oxide board in your next project, we’re here to help.

Contact Us Today to learn more about product specifications, bulk pricing, and international shipping options. Our experienced team is ready to support your project from planning to installation. Let’s build something safer—and stronger—together.