Fiber Cement Board Manufacturing Process

Fiber cement board is made by mixing cement, fine silica or limestone, cellulose pulp and water into a dilute slurry, forming it into thin layers on a sheet machine until the target thickness is reached, then cutting, stacking and often pressing the green sheets. The boards are cured either in air or in a steam autoclave, then dried, trimmed, sanded and tested.

That is the whole process in one paragraph. The rest of this article follows a board through the plant step by step, with the figures that control each step and the decisions a plant owner has to make before the line is configured: which curing route, which forming machine, whether to press, and which product standard the boards must pass.

The Fiber Cement Board Manufacturing Process at a Glance

The order does not change much between plants. What changes is the formulation, the forming machine and the curing route, and those three choices are linked.

Raw Materials for Fiber Cement Board

Fiber cement is a cement matrix reinforced with fibers. EN 12467 describes fiber-cement sheets as consisting essentially of cement, or of a calcium silicate formed by the reaction of a siliceous and a calcareous material, reinforced by fibers (EN 12467). In practice, a plant works with four groups of material.

• Binder. Ordinary Portland cement is the main binder.
• Filler or reactive silica. In autoclaved boards, finely ground silica sand reacts with the lime released by the cement during steam curing. In air-cured boards, limestone flour or other fillers are used instead. Global Cement’s industry overview lists cement, water, silica, limestone flour and fibers as the basic constituents, with optional silica fume, fly ash, metakaolin and processing aids (Global Cement, Cement Boards 101).
• Process and reinforcing fibers. Cellulose pulp does two jobs. It reinforces the board, and on the sheet machine it forms a filter mat that holds the fine cement particles while water drains away. Air-cured boards usually add synthetic fibers such as polyvinyl alcohol (PVA) for reinforcement.
• Water, most of which is recovered and reused.

Published formulations show how far the two routes differ. Swisspearl’s environmental product declaration for its air-cured boards gives 75–78% cement, 1–5% pulp and 1–3% PVA fibers by mass (Swisspearl EPD). Research on Australian autoclaved boards describes a matrix of Portland cement and finely ground silica, reinforced with about 8–10% refined softwood kraft pulp (Ni, 1995). These are published examples, not a recipe. Your cement, sand and pulp decide the final mix, which is why raw material tests come before the line is configured.

One practical point: cellulose can release sugars that slow the setting of cement, and kraft pulps release less of them (Global Cement, Cement Boards 101). Pulp grade is a raw material decision, not just a purchasing one.

Fiber preparation and slurry mixing

Pulp arrives as dry bales. It is broken up in water in a hydrapulper and then refined. Refining roughens and fibrillates the fibers so that they bond better to the cement and trap more fine particles during forming. Too little refining and fines wash through the sieve or felt; too much and the slurry drains slowly and the machine has to run slower.

The prepared fibers are then mixed with cement, silica or limestone, and water. The slurry for a Hatschek machine is very dilute, about 7–10% solids by weight (Ni, 1995). Batches are weighed, mixed and pumped to the forming section at a steady rate, because any variation in solids content shows up later as variation in sheet thickness and density.

Forming the Sheet: Hatschek or Flow-On

Forming is where fiber cement looks most like paper making. Both common machines build the board from thin wet layers that are wound onto a forming roll until the required thickness is reached.

• Hatschek forming. Rotating sieve cylinders sit in vats of slurry. Each cylinder picks up a thin film of solids as water drains through its mesh and passes the film to an endless felt running over the top of the cylinders. The felt carries the combined layers over vacuum boxes, which remove most of the water, and on to the forming roll (Ni, 1995). Patent literature describes individual films of 0.1–0.6 mm (Redco, US 10,144,150).
• Flow-on forming. The slurry is applied directly and continuously onto the moving felt, dewatered by suction and wound onto the forming roll (Nichiha, US 8,043,461). Each revolution adds a thicker single layer, so fewer revolutions reach the same board thickness.

Both machines are proven. On the board lines we supply, flow-on forming is the more common choice: the equipment is simpler, energy and running costs are lower, it is more tolerant of variation in raw materials, and it uses less water. For high outputs, our reference designs use a twin-roll board machine. The mechanics of the Hatschek machine, and a side-by-side comparison with flow-on, are covered in The Hatschek Process for Fiber Cement Sheets.

When the layers on the forming roll reach the target thickness, the wet sheet is cut across the roll and peeled off. The roll’s circumference sets the length of the raw sheet, and the sheet is then trimmed to final size.

Stacking, Pressing and Pre-Curing

Green sheets are soft and full of water. They are stacked, usually with steel templates between them, so that they keep a flat, even surface while they gain strength.

Pressed or unpressed board

Many products are left unpressed. For higher density and strength, the whole stack goes into a hydraulic press. Pressing squeezes out water, closes the pores and improves the bond between layers. Swisspearl’s EPD describes the boards being stacked with intermediate layers and pressed before hardening (Swisspearl EPD).

On our reference designs, presses of 5,000, 7,000, 10,000 and 14,000 tonnes are matched to board density and output. The tonnage is not a quality claim in itself. It has to suit the stack size, the board size and the density the product standard and your customers expect.

Pre-curing

After forming or pressing, the stacks rest until the cement has set enough to handle the boards safely. James Hardie’s patent literature describes pre-curing of up to 80 hours, most preferably 24 hours or less, before the main cure (James Hardie, US 6,572,697). In a plant, the pre-curing time sets how many templates and how much floor space the line needs.

Curing: Air-Cured or Autoclaved Fiber Cement Board

This is the decision that shapes the whole plant. Fiber cement can be cured at ambient conditions, or with high-pressure steam in an autoclave.

Air curing needs less equipment but more storage space and time. In Europe, mixtures of PVA and plant fibers have been used successfully for air-cured products (Ni, 1995), and Global Cement notes that the air-cured route is well suited to roofing products (Global Cement, Cement Boards 101). Autoclaving needs a silica mill, a boiler and pressure vessels, but boards leave the plant quickly and at full strength, and the silica in the mix reacts during the steam cure.

On our reference designs, autoclaves are fitted with steam recovery: exhaust steam from one autoclave heats the next, saving about 25–30% of the steam input. Because the boiler and autoclaves are among the largest energy users in an autoclaved plant, this is worth asking every supplier about.

Demolding, Drying, Finishing and Water Recovery

After curing, the boards are separated from the steel templates. Boards that stick to the templates are a common cause of breakage, so our reference designs include an automatic board release unit after the autoclave. The templates are cleaned and returned to the stacker.

Cured boards still hold a lot of water and must be dried to a target moisture content before they are cut and packed. Boards that are packed too wet can warp or shrink after installation.

Finishing then brings the board to its sales specification:

1. Edge trimming to final length and width.
2. Sanding of one or both faces where the market expects a calibrated thickness or a smooth surface.
3. Inspection of thickness, flatness, edges and surface. Our reference designs check boards on the line, so defects are caught before packing.
4. Coating if required. Many facade boards are coated on the visible face; Swisspearl’s EPD describes two coats of acrylate paint (Swisspearl EPD). A UV coating line for stone and wood patterns can be supplied with the board line or added later.
5. Packing on pallets with edge protection.

On our reference designs the standard board is 2440 × 1220 mm, with 2400 × 1200 and 3660 × 1220 mm also made. On the same designs, fiber cement board is made from 3 mm up to 30 mm thick, at a density of 1.4–1.8 g/cm³.

Water, waste and dust

The sheet machine uses a great deal of water, and a Hatschek line in particular produces large amounts of waste water (Global Cement, Cement Boards 101). Well-run plants keep the process water in a closed circuit. Swisspearl’s EPD states that its process water is kept in a closed circuit (Swisspearl EPD). In practice this means settling tanks or clarifiers, return pumps, and recovery of the solids so that they go back into the mix.

Trimmings and rejected green sheets can be repulped and returned to the slurry. Cured offcuts and sanding dust are drier problems: sanding and cutting stations need dust collection, because boards made with ground silica produce fine dust. Plan these systems with the main line, not after it.

Testing Fiber Cement Board to EN 12467 or ASTM C1186

The product standard decides the formulation, the density and often the press, so choose it before the line is configured.

• EN 12467 specifies requirements and test methods for fiber-cement flat sheets for internal and external wall and ceiling finishes. It sorts sheets into categories A to D by exposure (from heat, high moisture and severe frost down to rigid underlayer use) and into five classes by bending strength. It does not cover sheets for fire protection purposes (EN 12467). Gulf markets use it as GSO EN 12467.
• ASTM C1186 covers non-asbestos flat fiber-cement sheets for exterior applications such as wall claddings, facades, curtain walls and soffits. Type A sheets are for exposure to sun, rain or snow; Type B sheets are not directly exposed. Sheets are graded into four grades by flexural strength (ASTM C1186). The current edition is C1186-26.

A plant laboratory therefore needs at least bending strength, density, water absorption and dimensional checks, plus the durability tests the chosen category or type calls for. Strength should be checked in both directions: research on Australian boards measured dry flexural strength of about 19.2 MPa along the machine direction and 13.5 MPa across it for the same 6 mm sheet (Ni, 1995). For a deeper look at each standard, see EN 12467 Fiber Cement Sheet Standard Explained and our article on ASTM C1186 for fiber cement producers.

FAQ

What raw materials are used to make fiber cement board?

Portland cement, a filler or silica source, cellulose pulp and water. Autoclaved boards use finely ground silica sand, which reacts with lime during steam curing. Air-cured boards use limestone or other fillers and usually add synthetic fibers such as PVA. Small amounts of processing aids may be used. Modern boards are asbestos-free; EN 12467 has a specific designation for non-asbestos technology.

What is the difference between fiber cement board and calcium silicate board?

Fiber cement board is cement-based and can be air-cured or autoclaved. Calcium silicate board is based on lime and a siliceous material that react in an autoclave, with cellulose reinforcement and often some cement. Both can be made on the same type of line with different formulations and curing settings. See Calcium Silicate Board vs Fiber Cement Board.

Do fiber cement boards have to be autoclaved?

No. Air-cured boards reinforced with PVA and plant fibers have long been made in Europe. Autoclaving is used when the mix relies on ground silica and cellulose only, and when the plant wants boards at full strength soon after curing. The choice affects the silica mill, boiler, autoclaves and curing space, so make it before the line is configured.

Why are some fiber cement boards pressed?

Pressing the stacked green sheets squeezes out water, raises density and improves the bond between the layers, which increases strength and lowers water absorption. Unpressed boards are lighter and easier to cut and fix. On our reference designs, presses of 5,000 to 14,000 tonnes are matched to the board density and output the plant needs.

How thick can fiber cement board be made?

On our reference designs, fiber cement board can be made from 3 mm up to 30 mm, with 4–24 mm the usual range for volume production. The sheet machine builds thickness by adding layers on the forming roll, so thicker boards take more revolutions and reduce sheets per hour.

Planning a Fiber Cement Board Plant?

See how forming, pressing, curing and finishing are configured for 3, 5 or 8–10 million m² a year on our fiber cement board production line page. Our calcium silicate insulation plant setup guide covers a different product, insulation board and pipe sections, but its planning sequence from raw material tests onward is a useful reference.

Sources

• CEN, EN 12467:2012+A2:2018 Fibre-cement flat sheets – Product specification and test methods (SIST adoption listing): https://iteh.es/catalog/standards/sist/e6248861-5e94-4617-a934-1a3c85c01195/sist-en-12467-2013a2-2018
• GCC Standardization Organization, GSO EN 12467:2024+A2:2024: https://ysmo.gso.org.sa/store/standards/GSO:869674?lang=en
• ASTM International, ASTM C1186-26 Standard Specification for Flat Fiber-Cement Sheets: https://store.astm.org/c1186-26.html
• Swisspearl Group AG, Environmental Product Declaration: Even boards, small and medium-size, made of fibre cement (IBU, EPD-SWP-20180028-IAD1-EN): https://www.swisspearl.com/media/6093/download/Even%20boards%2C%20small%20and%20medium-size%2C%20made%20of%20fibre%20cement.pdf
• Y. Ni, Natural Fibre Reinforced Cement Composites, PhD thesis, Victoria University of Technology / CSIRO Division of Forest Products, 1995: https://vu-9.eprints-hosting.org/15654/1/Ni_1995compressed.pdf
• A. Saunders and E. Davidson, “Cement Boards 101”, Global Cement Magazine, December 2013: https://globalcement.com/magazine/articles/825-cement-boards-101
• James Hardie Research, US 6,572,697 B2, Fiber cement building materials with low density additives: https://patents.google.com/patent/US6572697B2/en
• Redco NV, US 10,144,150 B2, Hatschek process for the production of fiber cement plates: https://patents.google.com/patent/US10144150
• Nichiha Corp., US 8,043,461 B2, Method for manufacturing fiber reinforced cement board: https://patents.google.com/patent/US8043461B2/en