Best way to seal up masonry around a chimney thimble?

[Skier76]

When cleaning up our hearth, I noticed I could see outside light around the thimble area of the chimney. I went outsided and moved back the unattached trim ring, I could see some pretty big gaps in the block.

The hearth is cement and rock slapped right up against the block foundation (best I can tell). Chimney is 8" "metalbestos". I've attached a few pics of the setup.

Combustibles thankfully aren't an issue here. What's the best way to seal up these gaps and make everything nice and air tight?

 

[begreen]

I would think cement for the big gaps in the block. Then a thick bead of silicone to bed the trim ring.

 

[MountainStoveGuy]

BG, we are on the same page on this one. If i remember correctly, you had a castine right? Im hoping this is 8" OD pipe.

 

[BrotherBart]

Personally I would stuff large stove gasket rope into the void. Inside and outside.

 

[MountainStoveGuy]

rockwool would work too.

 

[Skier76]

Well! Got some interesting results when I googled "Where to buy rockwool". Apparently, there are other uses for that stuff I never would have dreamed of. Will stove shop or home center have that stuff?

Thoughts on using some masonry screws to secure that trim ring along with the silicone? Of course, it's not perfectly flat, so it may need some assistance staying put.

8" ID on that pipe...I measure this weekend...measured twice.

 

[MountainStoveGuy]

you can get replacement blankets from your dealer, its the same stuff that will come on top of the baffel plate of your new stove. If you have a good garden supply, they also sell it for horticulture. The horticulture varity comes in cubes, and is more ridgid. We have used the cubes to insulate block off plates, just peel the plastic off.

 

[BrotherBart]

If you go looking for Rockwool it will be a long hunt. Mountainstoveguy's advice on the garden supply places is probably good advice. Personally I screwed the finish collar to the the blocks on my stove in the basement office. No need for masonry screws. Big sheet metal screws do just fine.

 

[EatenByLimestone]

Your stove shop probably sells kaowool.

Matt

 

[Skier76]

Yep, that is class A. Thanks for the tip regarding the clearance; I wasn't aware of that.

Good call on the screws for the trim too. Again, I hadn't thought of that.