I finished a new liner install this past weekend. It went well but one of the issues I had is that the chimney flue is 12x18 rather than 12x12 so the 13x13 flashing top plate in the kit wouldn't work. The existing chimney had a concrete cap elevated by a couple bricks in each of the corners so we knocked the bricks down and the cap fit fairly flush on the top of the chimney. We cut a square hole in the cap and fit the liner through that and put the top plate on the cap with some RTV and that part of the install really went well,(hat tip to MALogger for the idea).
But, there are some small gaps between the concrete cap and the top row of bricks it sits on. Some of the gaps are fairly small like 1/8" but some are closer to 1/2". I'm looking at options to seal up the rest of the chimney in order to keep the wind and water out and keep the liner temp from cooling too much although it is insulated with 1/2" ceramic wool from above my damper to 1 foot below the cap. I was wondering if it would get too hot in the general area to use Great Stuff or some other expanding foam even though the liner is insulated and there is a fair amount of clearance on the 6 inch liner in a 12x18 flue. The foam would be the easiest to apply. I was also thinking maybe RTV or concrete caulk but those would be harder to apply. I was also thinking of just stuffing insulation in the voids as well. Any ideas are appreciated.
But, there are some small gaps between the concrete cap and the top row of bricks it sits on. Some of the gaps are fairly small like 1/8" but some are closer to 1/2". I'm looking at options to seal up the rest of the chimney in order to keep the wind and water out and keep the liner temp from cooling too much although it is insulated with 1/2" ceramic wool from above my damper to 1 foot below the cap. I was wondering if it would get too hot in the general area to use Great Stuff or some other expanding foam even though the liner is insulated and there is a fair amount of clearance on the 6 inch liner in a 12x18 flue. The foam would be the easiest to apply. I was also thinking maybe RTV or concrete caulk but those would be harder to apply. I was also thinking of just stuffing insulation in the voids as well. Any ideas are appreciated.
