Having recognized my lack of experience in blockwork, I got my pal and neighbour Dave to come and spend a day working on it. Dave, being a builder, has plenty of experience with block and he sure did earn his money.
First though, the floor needed to be ready to receive the block. This meant a stabilizing sheet of ply and lots of screws, and several sheets of vermiculite board. You can use loose fill vermiculite for all kinds of things and it is very cheap. Vermiculite board is quite a bit more expensive but it has good compression strength, a rated operating temperature of 900 degrees celcius and provides excellent insulation. Guy and I spent half a day measuring, cutting, screwing down and figuring out how to get the vermiculite board to cover the required area without wasting too much of it. In the end it looked like this:
The last bits to go in were those two small dark triangles. The ones that look like the eyes, under a massive turban. As soon as I fitted them Guy said "Oh, it's a computer-generated genie."
It makes me irrationally happy to think of him down there, insulating the floor and keeping us safe from bakery fires.