alternative sealants for liner/stove connection

[DavidV]

For the offset connection and for the blockoff plate I used rutlands fireplace morter that comes in a caulk like tube. it becomes brittle and cracks/breaks after it's been in use for a little while and I'm wondering what others use for the connections to flue pipes, etc. Is there something that will withstand the heat produces without cracking?

 

[elkimmeg]

Dap makes a product called high heat motar Blask color ASTM-e 136 certified good for 2000

All firestop draft sealants rated to 136 standard will work they have the necessary heat range
Boss makes one tested to 3000 degrees
home Cheopo sell a grey color version made by 3M I find it to flow better and seems less prone to cracking