Sealing Wall Thimble in a concrete wall

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MTBSully

New Member
Oct 8, 2021
9
03840
Hello All,

Recently had my foundation cored and installed my thimble and through wall chimney pipe. The thimble is through my concrete foundation and within the thimble I am using triple wall class A chimney pipe. The picture below highlights my question. There is a very small gap between the thimble and the concrete wall, as well as the triple wall pipe and thimble. What can i use to seal these up? Some sort of non combustible insulation, foam or sealant? I can feel a significant draft through these areas so im sure they arent intended to be left like this. What products do you recommend? Thanks!

20211128_103124.jpg
 

begreen

Mooderator
Staff member
Nov 18, 2005
93,152
South Puget Sound, WA
It can be cemented in, or stove door gasket can be used. Follow with a bead of divine or RTV.
 

MTBSully

New Member
Oct 8, 2021
9
03840
Im thinking some black silicone RTV. The GE silicone is rated to 400F and the class A pipe should get anywhere close to that hot