I need to caulk in a damper that I just added to an old fireplace. Anyone know of a caulk that will do the job and resist the heat of an open wood fire? Much obliged. Charlie
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You need more than heat resistant. That location is the hottest spot in your fireplace. It needs refractory cement. Anby place that sells masonry supplies. Read the lable. Some requires wetting of the materials first.
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Further on Piffin's post. The caluk should not be confused with Firestop Caulk. There are several brands out there which are meant to be caulked into the conduit or utility rund in a fireproof wall. True it doesn't burn, but it does expand to fill the gap when heat is introduced. If you mistakenly put that firestop stuff in the breach of your damper it would expand and fill the damper opening or something equally as awful.
There is probably a guy in your town that deals in refractory brick mortar and the usual stuff for fireplaces. My local guy sells it to factories and foundries for their use. Don't use regular brick mortar or you'll be doing it again real soon. PS the link below tells the story but pay attention to the size of the mortar joint. Most are under 1/8 inch If it is more than that you may want to work the old bricks down to a smoother seat.
I got a great link from one of the guys on this site (sorry I can't find out who gave it to me when I'm typing a reply, but rest assured it was a brilliant guy) on fireplaces at http://www.bia.org/ The brick institute has all the information you need.
Look under fireplaces and they will have all the pertinent poop. I must have printed 50 pages.