due to the nature of my install (through a block NON-combustible wall with supervent pipe) we will not be using a thimble as it is optional for a non combustible wall with supervent. My horizontal section through the wall will be disconnected when I clean the flue so I don't want to mortar my chimney pipe to fill the small gap between my wall hole and the chimney pipe. Is there any type of fire proof insulation that can be used to fill the void around the pipe that I could just remove and re-install when I need to clean the flue? This is a wood stove application