[Wiley]

Peter,
Thanks for your thoughts :-)

My plan (subject to change, of course) is to cover the dome with a layer of aluminum foil. The refractory will be a concrete mixture using calcium aluminate cement and crushed basalt. The plan is for this to be mixed in small batches and hand packed upon the dome in a somewhat orderly fashion, but with definite expansion joints (probably with aluminum foil) between "blocks" of the refractory. My calculations put the expansion of the dome at less than 1/4 inch, that's radius of the sphere, for a 800 degree F differential. But the idea is the refractory can expand and contract and nothing will fall out and into the pizza. The loss from the lack of refractory where the cracks form will, I expect, be minimal, and the steel will "bridge" the cracks making for a uniform radiant surface. And when it cools it all shrinks back together.

The expansion of the whole will hopefully be allowed by a layer of Frax (insulating blanket) which covers the refractory. Over that will come the vermicrete and over that the stucco. If that fails and I get cracks on the outside of the dome, then I will turn to a rectangular "house" over the dome with the loose vermiculite etc. That is not my first choice I prefer the curves of the dome/igloo shape.

Wiley

And here's a photo of the entrance with the bottom ring ground to the height of a standard refractory brick.