Fire brick layer - refractory mortar together or leave un-mortared?

[moonrattles]

Hello - we are finishing the bottom layers of our WFO (using a refractory cement 4 piece form for the oven itself we bought off CL from a guy who used to live in Italy and bought there to install here, but never did)
We have CMU built base with a 4" layer of concrete weight bearing slab and then a 4" vermicrete slab we finished this last weekend. I was able to score some older fire brick reclaimed from army houses here from 1950s for a layer of firebrick before we set down the oven base. Question is - do we place the firebrick tight against each other but free on top of the vermicrete or do we use a thin layer of refractory cement between them to make the firebrick layer "permanent" - my husband feels we need to do the latter for weather protection (no plans currently to build a "cover" for the oven space) unless we decide to do an adobe layer on top of the firebrick as part of the "decorative" outer layer (or even if we do the decorative adobe). We will be putting ceramic fiber blanket around the dome and then a 10:1 vermicrete around that and then adobe the dome, but haven't yet figured out what to do with the platform portion and the join of the two.

Thanks for any thoughts. We moved to the islands last year and this is our first WFO at home and have found supplies a lot harder to come by here - no cause for things like warm insulation in the tropics.

[admin]

Floor - Heat conductivity is typically better if the firebrick touches, so if you use mortar between, make it as thin as possible.

Dome - Some of the best oven makers will fit the brick so tight, it only needs to be skinned. Use the firebrick to fit the oven dome, mortar bonds it, but balance strength with tight fitting brciks inside the chamber and "V-ing" out to the outer shell.

Skinning the Dome - You can use vermiculite to skin the dome at about a half inch layer. This will create a protective shell holding the oven together. 10:1 is too soft and spongy. Consider doing it at 5 or 6:1

Insulation - Use the insulation blanket to insulate the oven, lathe and finish it with the vermiculite / concrete mix. If the insulation is good, than the seal of vermiculite can have more concrete on the outer shell from strengh. We prefer a stucco finish coat with sealkrete or equivalent sealant.

[moonrattles]

Thanks admin! We won't actually be fire bricking the dome - the dome is already refractory cement form and we will be using the ceramic fiber blanket/chicken wire, then vermicrete etc.

I have seen lots of pictures of what looks like people have finished the deck/table the dome is on - with tiles, adobe etc - so assume that is fine to do - whether we mortar between or not?

[admin]

The deck must be non-combustible material, stone / marble etc is a matter of taste. There should be insulation between the deck and oven floor. In Layers Deck - Insulation - Sand / Mortar - Floor / Dome.

You can use the insulation board from the link above or a vermiculite mix.