Chimney wanted to charge me over $250 to fill a roughly 1 inch gap in my firebox that exposed some of the insulation. A 16 ounce can. This filled one side of my firebox perfectly. I followed her healing instructions. Made a small fire and let it burn a little and then got it nice and warm a little longer. No bubbles or anything unwanted at the end of the process. This stuff is rock hard. I felt good about finishing one side and just ordered another 16oz to finish the other.