Refractory Mortar is a dry, preblended mortar ideally suited for setting masonry units in fireplace (outdoor or indoor), fire pit or chimney applications. Best used when laying fire brick or clay masonry in high-heat applications. Chromite Sand is a naturally occurring spinel consisting primarily of the oxides of chrome and iron. It is a by-product of ferro-chrome production and is mainly used in foundry applications and in glass producti