This morning I pulled my stove pipe out of the chimney to take a look in the pipe. There was some creosote in there but it wasn't built up too bad. Maybe an 1/8 of inch thick. The problem was when I went to pull the stove pipe out the entire silver collar came right out of the chimney and some of the mortor broke away creating a nice gap as you can see in the pics below. What should I use the fill the gap with and can I get it at Lowes or Home Depot? Should I worry about that silver collar coming right out of the chimney? It seems to have gone back in as far as it was before.