Mortar inside arch to dome or not

[Jim from Akron]

I've heard that some people mortar their dome to their inside arch, and some people leave a gap and fill it with high temp caulk. What are the advantages/disadvantages to each approach?

[Jim from Akron]

Here are a couple pics of how my dome and arch are lining up. Again, my question is should I mortar between the dome and arch, or should I leave the gap and fill it with high temp. caulk so that the two can expand/contract independently?

[UtahBeehiver]

Pics are too small to see detail. But I did stuff my arch and dome gap with a ceramic fiber rope then use a high temp caulk (2400 F) to keep the CF fibers encapsulated. I don't think this brand of caulk is available any more but there is one called Kaowool Moldable Caulk by Thermal Ceramics.

[david s]

All the high temp caulks I've tried go hard and don't retain flexibility. High temperature silicone which does remain flexible will not withstand sustained high temperatures seen at the top of the oven mouth (flame will often lick around the oven mouth there). The quoted max temp resistance of high temp silicone is intermittent only. Russell's solution of ceramic rope, which is flexible and heat resistant enough at that location is a good one. My approach is a little different. The idea is to reduce conductive heat leaking into the heavy thermal mass of the flue gallery, thereby reducing the heat sink effect. I have designed a much lighter flue gallery (9 kg), cast in one piece to reduce overall weight and to also reduce the heat sink effect. It is an integral part of the oven connected with refractory mortar and insulated in the same way as the dome. My heat conductive break (of around 8mm) is between the flue gallery and the outer decorative arch which is integrated into the outer rendered dome shell. In this way the inner oven parts (dome and gallery) can freely expand and contract within the outer dome shell and decorative arch. (I have seen ovens with quite severe cracking in the outer decorative arch that I'm sure are caused by thermal expansion of inner parts against the cooler decorative arch). The 8 mm gap between the oven floor and decorative arch is filled with ceramic fibre blanket and topped with 6:1 vericrete which is somewhat flexible. the sides and top of this 8mm gap are just air.

There are probably other solutions to this problem, let us know what you come up with. You are on a fascinating journey along with many others, freely willing to share experiences, experiments and solutions.