I propped the arch for on four jackposts, high enough to lift the weight of the arch from the walls. This allowed me to straighten the walls a little and pop in the fallen brick. I couldn't completely correct the spread tho - I'd need to pull down the walls for that. I might do that next summer but for now I need to get this kiln working again - I have orders to complete. So! Because the walls had spread, there was an inch & a half gap in the front ring of the arch, and a much narrower wedge of gap in the second ring.
Tyler Gulden - let me here put in a 100% sincere plug for him: if you have a few bucks to hire your kiln built, he's the guy you want, and his services are affordable to the point of ridiculous!Anyway, on his suggestion I got a commercially produce high-alumina castble product called Noxcast 32, durable to 3200°F and non-reactive to soda. When I do my someday-rebuild, I am going to line the interior of the kiln with this stuff!
It comes in a 50 lb bag - way more than I need but whatev - and cost about 50 bucks. If it works it'll still be a bargain!
I needed it not to stick to the wooden arch form, so I melted paraffin wax & poured it into the gap, then heavily applied cooking spray. I mixed the castble into a thick-but-pourable consistency, then scooped & dribbled it between the brick until the space was filled.
It will need to set overnight but by tomorrow AM I should know if we are good to go!