Calcium silicate (often referred to by its shortened trade name Cal-Sil or Calsil) is the chemical compound Ca₂SiO4, also known as calcium orthosilicate and sometimes formulated 2CaO. SiO₂. It is one of group of compounds obtained by reacting calcium oxide and silica in various ratiose. e.g. 3CaO-SiO₂,Ca₃SiO₅; 2CaO-SiO₂, Ca₂SiO₄; 3CaO-2SiO₂, Ca₃Si₂O₇and CaO-SiO₂,CaSiO₃. Calcium orthosilicate is a white powder with a low bulk density and high physical water absorption. It is used as an anti-caking agent and an antacid. A white free-flowing powder derived from limestone and diatomaceous earth, calcium silicate has no known adverse effects to health. It is used in roads, insulation, bricks, roof tiles, table salt and occurs in cements, where it is known as belite (or in cement chemist notation C₂S). Calcium silicate passive fire protection board being clad around steel structure in order to achieve a fire-resistance rating