32" build in Calgary, AB - pompeii neapolitan

[david s]

ok, so while I already have 5 ceramic fibre boards 18lbs/cu ft each 12"x36"x2", I have bought to be delivered July 10th 8 Skamol calcium silicate boards each 58cm x 24cm x 4cm. I want to design my oven for certain conditions with 1000F inside and at ambient temp outside of lets say 100F, would those two layers of casi+cfb equivalent to about 3.5" thick be enough on that hot day and hot oven firing that concrete slab under them wont reach more than 125F? otherwise if I add a 2.5" 5:1 perlite cement under then do I need to worry about Calgary winter freeze(--37c in extremes I seen that average -25c easily ) that it would destroy the moisture soaked perelite-cement layer causing unstable base?

casi+cfb at 3.5"thick, what else do I add if any:
1) nothing, concrete slab gonna be very fine under them
2) 5:1 perlite cement layer 2.5" thick, how to deal with winter freeze as the temp wont reach boiling point on it to evaporate water in it
3) loose perlite in a container made of pavement concrete bricks mortared to base slab and tampered or crushed a bit, lets say about 3" thick
4) another 1" or 2" casi?
5) another 2" ceramic fibre board?

I am using 2 bags of Quikrete Sand/Topping Mix 25KG Model # 110326 to level the slab as well as green self levelling laser level on tripod. I guess most likely no need for the 2.5" perlite-cement layer

My feeling is that your best option is to go for number 1, given the following. Not sure what others would advise.

Insulation thickness wonders to the law of diminished returns.

The denser the material the poorer the insulation value.

Insulation ability to hold heat is a function of time.

Any moisture present drastically reduces insulation value because it is conductive.

Most insulating materials are very hygroscopic (except foam glass)

The best insulator is a vacuum.

[IH123]

I used today1.5 bags of "Quikrete Sand/Topping Mix 25KG Model # 110326" to level the top slab, only where oven foot print will be,~52"x~52" . I used my laser level to check everything. one back side of the layer was almost zero and front level was the thickest at about 1.5".

I will mostly proceed with the casi 40mm+CFB 2" insulation only. now waiting for everything to cure and keep thinking every day if I should cast a castable refractory doughnut under dome walls or lay it directly on top of CaSi board. if I was to not use doughnut support, it will be dome bricks==> CaSi==> Ceramic Fibre Board==> concrete slab with hearth will be same, as well as archway. if I was to cast a castable refractory doughnut then only the dome will be different that the dome bricks first course will set on a 2.75" thick doughnut 32" inner diameter 42" outer diameter(1" thick extra for edging protection and expansion of dome) and will skip first dome spring/soldier course to compensate for extra height.

after 4 hours, got a misting and covered with vapour barrier and tarp

[IH123]

my plan for the insulation and support stack as my oven design will have dome, hearth, and archway NOT connected , rather have ceramic fibre rope/paper between them to locks air and heat. that is a stand alone shell oven. while aluminum foil could trap moisture, it will also seal the fiber dust from the board as it allows the thin castable refractory moisture to not be absorbed by the board

[david s]

Aluminium is highly conductive. It only works to reflect radiant heat when surrounded by air. Just as it is useless if installed touching a steel roof. Apart from this issue when used anywhere in an oven it can also create a vapour barrier. This can be partly offset it the foil is perforated. Another example of this is the perforated pizza trays sometimes used in an effort to stop pizza bases being soggy. Best to cook them directly on the firebrick floor.