See the attached pic. The sealant fell off partially exposing the opening where the stack vents into the chimney. I also see a white cotton(asbestos ???) material between the stack and the wall of the chimney. My questions are: Should I duct tape this exposed area as a temporary fix until I get a sealant to cover it up? I also have metal (aluminum) tape. What is the sealant material I should use for a long term fix? Thanks for any tips.