cleanburn castable refractory cement - 25lb pail cleanburn cleanburn castable refractory cement is a dry-mix cement that dries as hard as fire brick. perfect for casting into custom designs, as it will hold its shape while drying; building firepits, and much more! durable to be only material when casting a solid stove bed or outdoor oven. durable, and strong - it also works to fill large holes or cracks in masonry. effectively replace mortar and use it for for tuck-pointing. may require layering for thicker applications.