MgO Board Manufacturing Process: From Magnesia Slurry to Finished Sheet

MgO board manufacturing turns light-burned magnesium oxide, a magnesium sulfate (or chloride) solution, fillers and glass-fiber mesh into flat building boards. The slurry is batched and mixed, laid in layers with mesh on templates and roller-pressed to thickness, then stacked to cure at ambient temperature. Boards are demolded, cured and dried further, and finally trimmed, sanded and inspected.

What MgO Board Is Made Of

An MgO board is a thin, fiber-reinforced slab of magnesia cement. The binder forms when reactive magnesium oxide reacts with a concentrated magnesium salt solution. Our MgO board lines make magnesium oxysulfate (sulfate) boards, so the salt is magnesium sulfate; older and some current lines use magnesium chloride. The chemistry behind that choice, and why it decides how the board behaves in humid air, is covered in magnesium oxysulfate vs oxychloride MgO board.

The activity of the magnesium oxide matters as much as its purity. Calcination temperature controls it: MgO burned at about 600–1000 °C is reactive, while hard-burned and dead-burned material reacts little or not at all (Ahmad et al., 2024). A high total MgO figure can hide a weak product. In one 2026 study, a light-burned magnesia analyzed at 93.2% MgO but only 63.2% active MgO by the hydration method (Jin et al., 2026).

Modifiers are small in quantity and large in effect. For oxysulfate binders, citric acid, boric acid and trisodium citrate at 0.5–2.5% of MgO weight all improved strength and water resistance and reduced drying shrinkage in a Journal of Materials in Civil Engineering study (JMCE, 2018).

The MgO Board Manufacturing Process at a Glance

On our reference design the line runs in this order:

1. Raw material receiving and testing. MgO, magnesium sulfate, fillers and mesh are checked before they are released to production.
2. Solution preparation. Magnesium sulfate is dissolved to the set concentration and allowed to clear.
3. Batching and mixing. MgO, fillers and modifiers are dosed into the solution and mixed to a slurry.
4. Template preparation. Clean forming templates are fed to the forming machine.
5. Mesh laying and layered forming. Mesh and slurry are laid down in layers on the template and roller-pressed to thickness.
6. Stacking. Formed boards on their templates are stacked for curing.
7. Initial curing. Boards set and start to lose water at ambient temperature.
8. Demolding. Boards come off the templates, which are cleaned and returned to forming.
9. Second curing and deep curing. Boards continue to harden and dry off the templates.
10. Trimming, sanding and inspection. Edges are sawn to size, faces are sanded and boards are checked.
11. Packing. Boards are stacked on pallets, protected from rain and humidity, and labeled.

There is no autoclave and no steam boiler; the only thermal equipment is an optional heated curing room.

Batching and Mixing the Magnesia Slurry

Batching sets much of the board’s quality, because the binder chemistry starts the moment MgO meets the solution.

Solution preparation. Magnesium sulfate is dissolved in tanks with agitation, then held so undissolved material and impurities settle. Concentration is checked by density before every batch, and temperature matters too. One US patent for a chloride-free MgO board dissolves the sulfate in water warmed to about 40 °C, cools the brine below about 35 °C and checks it for clarity before adding MgO, which is then mixed in at about 25–45 °C, preferably below 35 °C (US11319249B2).

Dosing. MgO and fillers are weighed from silos or bins, the solution is metered, and modifiers are added by weight or as a pre-made solution. Accuracy on the modifier matters because the dose is small. Activity varies between suppliers and between lots, so each new MgO lot should be retested before it goes into production; a lot that is more or less reactive than the formula expects gives soft or cracked boards.

Mixing. Mixers bring the slurry to a workable consistency. The same patent mixes for about 15 minutes to workability and warns against mixing longer than 1.5 hours, to avoid crystallization under turbulent conditions (US11319249B2). Each batch should be used by the forming machine well within the slurry’s working time. Retarding modifiers lengthen that time: 1% boric acid delayed setting to 73 minutes in a laboratory study cited by Jin et al. (2026).

Laying Glass-Fiber Mesh and Forming the Board

On our reference design, boards are formed in layers with glass-fiber mesh on templates and roller-pressed. A typical forming sequence is:

1. A clean template, treated so the cured board releases from it, enters the forming machine.
2. A layer of glass-fiber mesh is unrolled onto the template.
3. A face layer of slurry is spread over the mesh.
4. The core layer, richer in filler, is laid on top.
5. A second face layer of slurry and a top mesh layer follow.
6. Rollers press the layers together, embed the mesh and bring the board to its set thickness.
7. The formed board moves on its template to stacking.

The mesh sits close to each face because that is where bending stresses are highest. If it drifts toward the center, the board loses bending strength; if it shows at the surface, sanding will cut it. Mesh tension, layer thickness and roller gap are set together and rechecked at every thickness change. The template face becomes the board face, so a smooth template means less sanding.

On our reference design the standard sheet is 2440 × 1220 mm, with 2400 × 1200 and 3000 × 1220 mm also common. Thickness runs from 3 to 20 mm, most often 3–12 mm, at a density of 1.2–1.4 g/cm³. Forming and trimming are set up for the thickness range a plant fixes at the start.

Stacking and Curing: Where Plant Capacity Is Really Decided

After forming, boards are stacked on their templates and left to cure. On our reference design this is natural curing at ambient temperature, in three stages: an initial cure that sets the board and drives off water, a second cure, and a deep cure before trimming. Magnesium sulfate boards harden slowly, so cold climates, or a need to shorten the cycle, call for a heated curing room. It is an option, not a requirement.

Public sources give a sense of the conditions involved:

• A laboratory reference for oxychloride cement curing is 22–26 °C and 60 ± 5% RH. Phase 5, its main strength phase, begins forming about two hours after mixing and dominates at around 40 °C; curing at 75 °C may make it more susceptible to water (Ahmad et al., 2024). More heat is not always better.
• The US patent above cures its sulfate board at 20–35 °C and 50–90% RH for at least 13 days before demolding (US11319249B2). That is a cast board, not a layered one; layered lines demold once boards can be handled and finish curing off the template, but the range is a useful guide.
• The 5·1·7 phase that gives modified oxysulfate boards their strength starts losing water at about 200 °C (Jin et al., 2026), so any heated curing or drying is kept far below that.

For a plant, the important point is this: output is limited by how many boards can cure at the same time, not only by how fast the forming machine runs. The number of templates, the stacking system and the curing floor area must all be sized for full output. For a 1 million m² a year line on our reference design, we allow 8,000–12,000 m² of buildings on about 1.3–2.7 ha, with the curing stacks taking much of that space.

Demolding and Template Return

Once the boards are strong enough to handle, the stacks go to the demolding station. Each board is separated from its template, either by hand or by a semi-automatic demolding device. Boards move on to further curing; templates are cleaned, inspected, treated with release agent and returned to the forming machine.

Template handling is a quiet source of defects: residue marks the next board’s face, a warped template gives uneven thickness, and a damaged edge tears the board during demolding. Keep spare templates and a clear rule for retiring worn ones.

Second Curing and Drying Before Dispatch

Demolded boards are stacked with spacers so air can move between them, and left to complete their second and deep cure. During this stage the board continues to gain strength and its moisture content falls toward equilibrium with the surrounding air.

Boards that leave the plant too early can shrink and bow after fixing, and their binder is still changing. In a 2019 study by the Technical University of Denmark, the dry mass of two commercial sulfate boards rose 7–8% after seven weeks in humid air, while the chloride board’s fell slightly (Wøhler Nielsen et al., 2019). Finished boards are not inert, and the more complete the cure before dispatch, the less they change in the wall.

Practical controls at this stage:

1. Record the forming date on every stack so curing time is tracked, not guessed.
2. Check moisture content and dimensional stability on sample boards before release.
3. Keep curing and finished-goods areas dry and ventilated.
4. In cold seasons, move stacks into the heated curing room.

Trimming, Sanding and Inspection

Trimming. Edge saws cut the cured board to its final length and width and square the corners.

Sanding. Sanding machines calibrate thickness and give the face a uniform finish for painting, laminating or tiling. Boards sold as decorative substrates may go on to a UV coating line for stone, wood-grain or high-gloss finishes, in the same project or as a later upgrade. Sanding and sawing produce fine dust, which should be extracted at source.

Inspection. Every shift checks dimensions, thickness, flatness and appearance, and samples go to the plant laboratory. What the laboratory tests should follow the standard the boards are sold to.

Some of these tests are simple enough to run in the plant. The 2006 edition of China’s JC 688 standard for glass fiber and magnesium cement board, for example, holds a 200 × 200 mm sample at 30–35 °C and at least 90% RH for 24 hours and then checks it for water drops or dampness; later editions may differ. Longer humidity and corrosion tests, such as the 90-day BRANZ program, are usually run by external laboratories. A sulfate formula removes the chloride behind brine sweating and fastener corrosion, but it does not by itself guarantee a pass in humidity tests, so boards for humid export markets should be tested to PAS 670, ICC 1125 or the buyer’s standard.

Equipment in an MgO Board Line

A complete MgO board line on our reference design includes:

• Raw material handling: MgO storage and dosing, magnesium sulfate dissolving and solution tanks, filler dosing
• Mixing: slurry mixers matched to the forming speed
• Forming: roller-pressed layered forming machine with mesh unwinding, on templates
• Stacking and template handling
• Curing: natural curing area, with a heated curing room as an option
• Demolding and template cleaning and return
• Finishing: edge trimming saws, sanding machines and inspection
• Packing
• Quality laboratory: MgO activity, board density, bending strength and moisture behavior
• Option: UV coating line for decorative boards

A single line produces 1–3 million m² of board a year on our reference design. The capacity a buyer chooses should follow the local market, the climate, which sets the curing area, and the standard the boards must meet. Production problems that start in the plant, from sweating to bowing, are covered in MgO board problems. If you are comparing board technologies, the calcium silicate board manufacturing process shows how an autoclaved board line differs.

FAQ

What is MgO board made of?

Light-burned magnesium oxide, a magnesium salt solution, fillers and glass-fiber mesh. Sulfate boards use magnesium sulfate and chloride boards use magnesium chloride. On our reference design the MgO has 60–80% active MgO, the sulfate is made up as a 15–25% solution, and fillers are wood chips, bamboo powder or calcium carbonate powder. Small amounts of modifiers such as citric acid control setting and water resistance.

How is MgO board cured?

At ambient temperature, in stages: an initial cure on the templates, then a second cure and a deep cure after demolding. There is no autoclave or steam boiler. Magnesium sulfate boards harden slowly, so plants in cold climates, or plants that want a shorter cycle, add a heated curing room. Heat is kept moderate, since too much can weaken the binder phases.

Why does MgO board need glass-fiber mesh?

Magnesia cement is strong in compression but brittle in tension, and a thin board is loaded mainly in bending. Mesh laid close to each face carries the tensile stress, holds the board together when it is cut or screwed, and reduces cracking during handling. Its position matters: mesh that drifts toward the center adds little bending strength.

What limits the output of an MgO board line?

Usually curing, not forming. Each board stays on its template through the initial cure, so the number of templates and the curing area set the daily output as much as the forming machine does. A single line on our reference design makes 1–3 million m² a year, and for a 1 million m² line we allow 8,000–12,000 m² of buildings.

Can the same line make chloride and sulfate MgO boards?

The mixers, forming machine, templates, curing and finishing equipment are broadly the same. The differences lie in salt dissolving and solution handling, modifier dosing, the MgO specification and the curing schedule. Running both formulas in one plant risks chloride contaminating sulfate boards, so it is usually better to choose one route and design the plant around it.

Planning an MgO Board Plant?

The process is simple to describe and hard to get right: raw material testing, the modifier system and curing capacity decide the result. See how these steps are configured on our MgO board production line, and use the MgO board plant setup guide to plan raw materials, curing area and site before you compare suppliers.

Sources

• Ahmad, F., Rawat, S., Zhang, Y. (2024). Magnesium Oxychloride Cement: Development, Opportunities and Challenges. Applied Sciences, 14(7), 3074 — https://www.mdpi.com/2076-3417/14/7/3074
• Jin, K., Wang, H., Xue, H., et al. (2026). Mechanistic insight of white carbon black in regulating hydration and improving water resistance of magnesium oxysulfate (MOS) cement. Journal of Building Engineering, 130, 116958 (author manuscript, Brunel University repository) — https://bura.brunel.ac.uk/bitstream/2438/33613/4/FullText.pdf
• Modification of magnesium oxysulfate cement by incorporating weak acids (2018). Journal of Materials in Civil Engineering, 30(9) (record, University of Technology Sydney) — https://opus.cloud1.lib.uts.edu.au/handle/10453/132237
• US11319249B2, Structural assembly board and method of manufacturing same, MgO Systems Ltd (Google Patents) — https://patents.google.com/patent/US11319249
• Wøhler Nielsen, S., Rode, C., Bunch-Nielsen, T., Kielsgaard Hansen, K., Kunther, W., Grelk, B. (2019). Properties of magnesium oxide boards used as sheathing in exterior walls. MATEC Web of Conferences, 282, 02091 — https://www.matec-conferences.org/articles/matecconf/pdf/2019/31/matecconf_cesbp2019_02091.pdf
• BRANZ (2023). Research Now: Materials #3, MgO boards — https://www.branz.co.nz/documents/4290/BRANZ_RESEARCH_now_Materials_3_MGO_final.pdf
• BSI, PAS 670:2021, Magnesium oxide-based boards for use in buildings. Specification — https://knowledge.bsigroup.com/products/magnesium-oxide-based-boards-for-use-in-buildings-specification
• International Code Council, ICC 1125-2026, Standard for Specification of Magnesium Oxide Boards and Construction — https://shop.iccsafe.org/icc-1125-2026-standard-for-classification-of-magnesium-oxide-board-and-construction.html
• JC 688-2006, Glass fiber and magnesium cement board (standard record, chinesestandard.net) — https://www.chinesestandard.net/PDF/English.aspx/JC688-2006