Refractory Mortar is designed for use in kilns and furnaces; the internal structure of the kiln is laid in fire brick, with extremely tight mortar joints (1-2mm). The sodium silicate in the mortar then reacts with the surrounding air and causes the mortar to take an initial set, allowing the kiln or furnace to be fully constructed. The structure is then fired to its full operating temperature and the mortar vitrifies, fusing to the surrounding bricks and becoming a ceramic.