Fibre cement is a composite building material consisting of Portland cement, cellulose fibre reinforcement, fine silica sand, and water. The material is formed into sheets or planks and cured under high-pressure steam in an autoclave, producing a dimensionally stable, fireproof, rot-resistant product that has grown from a niche alternative to a mainstream siding material. Fibre cement captured approximately 15% of the United States siding market by 2024, making it the third most common cladding material after vinyl and brick.
Composition and Manufacturing
The standard fibre cement formulation uses approximately 40% to 50% Portland cement by weight as the binder, 30% to 40% finely ground silica sand as the aggregate and filler, and 8% to 12% cellulose fibre derived from wood pulp. The cellulose fibres, typically sourced from plantation-grown radiata pine, provide tensile reinforcement and give the uncured sheet sufficient green strength to be handled before curing. Water is added to create a slurry that can be formed into sheets on a Hatschek machine, a specialised piece of equipment developed by Austrian engineer Ludwig Hatschek in the 1890s for asbestos cement production.
The Hatschek process deposits thin layers of the fibre cement slurry onto a rotating drum screen, building up the sheet thickness one layer at a time until the desired thickness is reached, typically 5/16 inch (8 mm) for lap siding and 5/16 to 1/2 inch (8 to 12 mm) for panel products. The layered structure mimics the natural grain of wood and contributes to the material's resistance to crack propagation.
Autoclave curing is the critical step that transforms the formed sheets from a weak cement product into a durable building material. The sheets are placed in a large pressure vessel and subjected to saturated steam at approximately 180 degrees Celsius and 10 atmospheres of pressure for 8 to 12 hours. Under these conditions, the silica sand reacts with the calcium hydroxide released during cement hydration to form calcium silicate hydrates, a stable crystalline compound that gives fibre cement its dimensional stability, strength, and resistance to chemical degradation. Without autoclave curing, the sheets would remain susceptible to moisture movement and long-term strength loss.
James Hardie and Market Leadership
James Hardie Industries, founded in 1888 in Melbourne, Australia, and now headquartered in Dublin, Ireland, dominates the global fibre cement siding market. The company began producing fibre cement in Australia in the early 20th century and was, for much of its history, a manufacturer of asbestos cement products. James Hardie ceased asbestos production in 1987 and transitioned entirely to cellulose-reinforced fibre cement, developing the proprietary technology that underlies its current HardiePlank and HardiePanel products.