Heat Stop Premixed is a fire-resistent, grey-colored refractory mortar used for the installation or repair of high-temperature resistant firebrick and masonry in pizza ovens, boilers, fireplaces, flues, furnaces, incinerators, kilns, and wood stoves. This is an air-setting product which may be water soluble in service. Do not use in exterior applications or where excessive moisture is present. Resists temperatures to 2,500 degrees. Meets all state and national building codes. Meets A.S.T.M. C-199. You will need approximately 50 lbs. of product to lay up 100 firebrick. Shipped in a 15 and 50 lb. pails. Shipping is FREE for all orders (contiguous US only).