Newbie Mistake, Will I be Ok?

[Pizza-n-Jazz]

I have been working like crazy for 3 weeks and have come to the dome. After reading some stories about losing heat and other problems I am a little confused and worried.
I poured a 3 1/2 inch slab on the blocks and then 3 1/2 inch slab of the portland/vermiculite mix and added 18 fire brick splits under the dome floor area. Do I still need ceramic board at this point?

[phippsj]

From everything I have read you can use the FB board to replace the vermiculite, but you don't have to. I have seen in other builds where they used 4.5" or even more on the vermiculite slab. I did a 4" vermiculite with no FB board.

[Tscarborough]

Normally the floor is made with full fire bricks, but the splits will work, they just won't hold as much heat. You would not put insulation on top of them, then more firebrick on top of that, though.

[Pizza-n-Jazz]

Thanks for the reply, I came up short on the vermiculite by 10% and so I added the split bricks at the last second to take up some space. I think on page 29 of the FB oven plans it said this would help hold some heat. It was 10:30PM when this happen so going back to the store was not possible.
The portland/vermiculite mix is pushing 1 1/2 to 5 ratio (to make the pour)so I was a little worried when I read some posts about heat loss or not heating at all. I guess I should start working in the AM but being a musician I get my energy high at night time.
The one good thing is that I live around 400 pecan trees and wood is not a problem. Thanks again for the help.

[DrakeRemoray]

So you will have an extra thick floor on top of slightly thin (by 1/2 inch) insulation? It is going to have to be your call, but you really don't need extra mass in the floor. It will just make heat up take longer and really there is plenty of stored heat in the regular design without adding additional mass to the floor. This is somthing you can only fix now, so I would consider pulling up the floor and adding some additional insulating board (and this really mostly to get the floor up to the height you want). 3.5 inches would probably be OK on the insulation, but the extra mass could be a killer IMO.

[Neil2]

Or put on another 2 inches of vermicrete.

[Pizza-n-Jazz]

Sounds like I need to cut out the brick and insert a ceramic board. Glad the dome was not started. A million thanks and if I ever win the lotto you guys are set!!

[DrakeRemoray]

Did you set the splits down in the vermiculite? You may be able to just dig them out and pour another layer...
Also, I cannot view that picture...

[Pizza-n-Jazz]

DrakeRemoray, I put the picture in Photo Gallery under Hearth and Stand "David's Mistake". I think that taking out the brick and going with port/verm or ceramic will give me the 3 1/2 that I need. I have some 1200F pipe insulation but its fiberglass type, is this some that might work? Thanks

[azpizzanut]

Hello P n J,

I looked at your photo. Here's what I would do. Dig out the firebrick splits and pour the void level with 1:5 insulation. If you decide to put down insulation board, then place it so it will fit the oven footprint. Lay the full hearth bricks on top of the board.

Cheers,