., but I have a few major questions about that oven. First, either it lacks insulation completely under the floor, OR it lacks a sound structural layer under the floor. First you seem them set the thin Terra Cotta tiles, then they pour a layer over top of it. Either that layer is an insulator and adds no structural strength to those flimsy tiles, or it is structural and adds no insulation under the floor. .
It's easy to misunderstand what happening in a picture.Those terracotta looking tiles which look a lot like kiln shelves could just be getting marked or cut for some other later function just because that's the same material Stephano uses later in the building of the vent.
That being said I do think they are using these in the construction of the slab, because if you look closely you can see the triangular wire coming up from the tiles as well as horizontal wire passing through those triangles.We don't see it in a picture but they may have added rebar or 4 x 4 wire mesh to that.
This oven definitely has a structural slab.Most blocks here are 8 x 16 so it's clear to see in the picture there's at least 6 or 7 inches of something poured on top of the blocks.Either the tiles were cut to fit inside and flush to the top of the blocks and supported from underneath or hung from the rebar some way and then covered with 6 inch of concrete, Or as it looks in the pictures the tiles are cut to set on the blocks and the slab is poured on top of this.The resulting slab is 6 or 7 inches thick at its outer edge where it sits on the block and 3 or 4 thick on top of the tile.
One picture shows they have poured perlicrete on top of the slab.So the insulation is on top of the slab were it'll do the most good.As far as the tiles under the slab I cant speak to whether or not it insulates or how well.It seems as it would or they think so.Maybe they just didn't have any plywood
So to answer the question,It's gotta slab and insulation.
Sorry I started writing this 1 hour ago and I see that some of this has been coverd by T