Brick Oven pizza floor insulation

[TomFremont]

I have built a brick oven at home. The oven has 2 1/2 inch firebrick as the floor and sitting on a 3 inch concrete block. When we cook pizza, it turns out good except the crust does not get crispy. Is my problem related to not putting any insulation in the floor? If yes, can I do something now or do I need to rebuild? Can I use unglazed tile (2 of them stacked) on top of firebrick? The dome temperature does reach to ~800 and the floor shows 300-400.

[david s]

Yes, you must insulate between the concrete and the floor bricks. Can you remove the floor bricks?

[JRPizza]

Welcome Tom. Not having insulation under the cooking floor is a problem folks come here with and there are usually no easy fixes. I'd suggest doing a search here for builds that had similar lack of insulation and see what they have come up with. Adding some unglazed tiles will add to the thermal mass in your floor, but you already have plenty of thermal mass in the 3 inch concrete the floor is sitting on. You need to see if there is a way to get some insulation under the cooking floor or get used to doing mainly open fire cooking and moving the fire back and forth as you cook pies to keep the bricks under the crust well charged up.

[TomFremont]

I like to say Thanks to all of you. There is no easy way to remove the dome but I will have to try. I will pull the dome and put in a Ceramic Insulation board between the slab and the Firebrics. Will 3/4 inch thick board help?

[UtahBeehiver]

A minimum of 2" of CaSi or AlSi board is recommended for floor insulation. It should have at least a compression rating of 75 PSI at 5% compression and a K value of around 0.6 Btu.in/(hr.ft2.F)
at 600 F. This high tech material is very water absorbent so you need to also mitigate water from getting on to the slab and soaking up into the insulation. Wet or no insulation is one of the most common problems of poor oven perfromance.

[TomFremont]

Thanks again. One more question. Can I replace my current concrete slab with a slab with Perlite and Cement mix (5/2 ratio). Will this help with insulation instead of the board. For my construction, changing the slab will be an easier option.

[UtahBeehiver]

A pcrete slab is not recommended as the structural base and a 5/2 ratio does not really buy you much in terms of insulation. See attached table.

[deejayoh]

Just my opinion, but an inch of cal-sil under your existing brick is a better option than unglazed tiles on top of the firebrick. You want your cooking surface to be firebrick - that is what retains the heat. If you can get a bit of insulation between that firebrick and the concrete, it is better than nothing. An inch of cal-sil is not going to give you multi-day cooking - but it will make your 'day of' cooking much better. I think you'd get to the point where the heat loss from the exposed side (in the dome) is greater than the heat loss into the hearth.

What's the situation with insulation on the dome? is there any? if there is none, might be a "day of" cooking oven either way!

[TomFremont]

My dome has the Fire Insulation blanket in between perlite cement layers. It does not seem to be heat loss from the dome. Even with dome having ~900 degrees I can touch the outside of the dome. If I have to remove the dome in order to put in the new insulation on the floor, I might go with recommended 2".
Thanks you all.

[AdrianBond]

I'm glad you got help. Welcome aboard !