Calcium silicate board

Compressed calcium silicate (Ca SiO) is used mainly as back-up insulation in kilns and furnaces but can also be used in kilnforming operations.

Coloured with vegetable dyes to identify grade and maker, it burns to a white colour during the first firing. It is available through refractory suppliers, most commonly as 25mm or thicker sheets.

Calcium silicate has a very fine texture and is easily carved with a scalpel or Stanley knife, or sawn with woodworking tools.

As it has no fibre or other reinforcement it can be quite a brittle material. While it can be used as a low mass kiln shelf, it is not recommended for regular use as it can crack under load at any time, and especially during a firing.

Calcium silicate  is OK to use for moulds or carved underlays. However it is not as long lasting as Ceramaguard. The two are not directly comparable alternatives, as they are different in texture. Ceramaguard can be used as a mould material for strength whereas calcium silicate board can be used for fine texture.

Calcium silicate does not require a battwash as it does not stick to glass.

Whilst the cause is not fully understood, calcium silicate board laid flat on a hearth can become very slightly concave during a firing.