Insulation Dilemma?

[wolvis]

Interested in what the community think about the following dilemma.

- I have only ordered enough Fibre Board insulation (50 mm) to totally support the oven floor, but not the dome walls.
- Do I a) use the two pieces whole and have an insulated square, filling the rest in with perlite and or vermiculite concrete? Worried that the difference in structural support might end up destabilising the whole structure.
- Or b) cut round the shape of the oven floor and use the fibre board as a circle under the floor, embedded in an oven shaped island of perlite concrete?

- or , I suppose, c) bite the bullet and buy more FB board and pay the absurd delivery costs on top?

[david s]

The underfloor insulation does not have to extend to cover the whole supporting slab. It only needs to come out as far as the inner dome.. you can probably use off cuts of the calsil to fill most of the uncovered areas and use some 5:1 vermicrete for the rest.

[wolvis]

Thanks. I've now got enough insulation cover for the whole outer wall and inner floor, so I will put it under everything. Now I have to worry about getting the floor flat and the first course, soldier or not? I was told to expect a sand/clay bed of about half an inch thickness, into which I am bedding 3" fire bricks. My floor is contained within the dome wall, not supporting it, so if I have a half brick first course laid soldier fashion that will be 4 1/2 " tall, leaving the wall approx. 1" proud of the floor. Is that ok?