Pdx 42" update

[Giovanni Rossi]

Sorry, late to the party on this one. You could get an 8" chimney bottom plate, trim it to the height you need and anchor it to the top of the flue gallery. Then connect that to your transition collar with an 8" male-male union.

If you're firm on not wanting to drill into the flue gallery, you could have another go at smoothing out the enlarged hole and use a 9"-8" flue reducer and the union. But, those reducers are pricey.

[Macrinehart]

So today I made the first attempt to repair my flue gallery. This time I purchased a single-wall to double-wall pipe coupler. This coupler seals the interior of the two walls and it has a 3" deep and 8" diameter flang on the base which I felt would make an excellent coupler to the flue gallery.

to start I re-filled my gallery with wet sand. Then I centered this coupler on top and filled it with wet sand. Next I cleaned and dampened the already dried concrete-mix I previously molded in place. Using a concrete bonding adhesive, I made a slury of sand, concrete and adhesive per directions on the bottle and spread that around the top and exterior sides of my existing concrete-mix. Then I mixed up more of the casting home brew and used that to build up the flue gallery around the pipe coupler.

My experience at this point is that the wet concrete wanted to slowly slump. After messing around for a while trying to mitigate this without much success, I finally decided to wrap the damp concrete in plastic cling wrap with the hope that a little pressure from the outside could hold everything in place while it slowly dries. Finally, once everything was satisfactory I pulled the coupler out.

My hope is first that I get a reasonable bond between new and existing concrete. I presume if that works then once the material is set up I'll have to do a little work to get the coupler to fit. If it doesn't work, then I'll have to knock this gallery down and redo it.