Calcium silicate boards are manufactured from silica with lime and/or cement, usually incorporating cellulose fibres or softwood pulp and mica or exfoliated vermiculite filler, to produce a range of densities.
The high-density material is laminated under steam and pressure, while the lower-density material is produced by rolling followed by curing in an autoclave.
Calcium silicate boards, like gypsum boards, are noncombustible. The material is grey or off-white in colour,easily worked and nailed. Calcium silicate boards are durable, moisture-, chemical- and impact-resistant with dimensional stability and a good strength-toweight ratio. They are available with a range of smooth or textured factory finishes for interior or exterior use and also laminated to extruded polystyrene for enhanced insulation properties. Standard thicknesses range from 4.5–20 mm, although thicknesses up to 100 mm are available in the vermiculite lightweight
boards used for fire protection giving up to 240 minutes’ resistance. The standard fire-resistance class is A2-s1, d0. Typical applications include wall, roof and partition linings, suspended ceilings, fascias, soffits, weatherboarding and fire protection to structural steel -work. External cladding boards may be finished with a sprayed or trowelled render to produce a seam less finish. (The thermal conductivities of calcium silicate boards are usually within the range 0.13–0.29 W/m K depending upon their composition.)