Hercules, 1/2 Gallon, Furnace & Stove Cement, Use To Seal & Repair Boilers, Furnaces, Fireboxes, Flue Pipes, Stoves, Ducts, Kilns, Chimneys, Combustion Chambers, & Many Other Furnace & Refractory Applications, Unique Patented Formula MeetsOHSA Requirements Of Less Than 0.1% Of Crystalline Silica Content, Applies Exceptionally Smoothly, Can Be Used On Oil, Gas, Coal, & Wood-Burning Heating Systems, Adheres To Most Building Materials, Will Not Shrink, Crack, Or Crumble.