Chimney insulation mix is a vermiculite based concrete mixture that is poured between the liner and the chimney walls. This mixture is formed with water in a ratio of 3.5 parts insulation mix to 1 part water. This mix is available in 45 lb. bags and each bag will fill 2.5 cubic ft.
It's easy to work with. It will fill voids and cracks in the masonry work while strengthening the chimney walls. It cures into a lightweight, semi hard mass that supports a liner within the chimney and forms a thermal barrier that keeps the flue gases warm.
This product adds performance to your liner and is very durable. It is UL listed for zero clearance to combustibles. It will seal dangerous cracks and any voids that you have in your chimney. The mix eliminates moisture buildup between the liner and the chimney structure. It is accepted by building code officials and what's better is that it can also be removed.
You can also use this around terra cotta flues. This insulation is very important, especially for a chimney that is connected to a solid burning appliance, such as wood or coal. When the flue gases stay warm your draft will be considerably better which results in a more consistent burn and significantly less creosote.