What is this material you use for the dome?

The refractory grade castable that we use over the cardboard mould is made up of calcium aluminate cement and a variety of compatible aggregates.

Calcium aluminate cements were invented in the 1800's and has proven itself in many high temperature environments 

Over the years I have had lots of customer feedback about the ovens.  I have had many customers who have had previously built brick ovens tell me that the performance of their new oven using the refractory causable is exactly the same.  They haven't noticed a difference except they are extremely pleased with how much easier the oven was to build!