Question: Dear Craig: First of all thank you for your updates and web site. We have a metal woodstove insert in our red brick fireplace. We cannot get anything to adhere to the metal to seal the air space. We follow the instructions, heat up the woodstove, apply, let it cool down, but of course the material shrinks down and eventually falls off in huge strips. Any ideas/experience with this sort of situation? Answer: Depends on where you are trying to do the sealing. When we install an insert into a fireplace, we make up a custom sheet metal pan for an area immediately above the fireplace opening (on a level plane)...This can fit quite tightly. A hole is cut through it to accept the flexible stainless steel tubing that is used to start to smoke up the chimney. Silicone sealant is good to 500-700 degrees and is great for an areas that do not come directly in contact with a single wall portion of the pipe of stove. Furnace cement is quite brittle (as you've found out) , but the Rutland brand is very good and takes heat up to 2000 F. Another option is stove door gasketing, which is made in many different sizes. This can be pressure fit, or glued in with silicone or furnace cement.