New Pompeii build near Boone, NC, USA

[DanR]

Hi Folks,
I have been popping in and out of the forum for years, finally gathering supplies. I just had repairs made to my chimney and have several cinder blocks and clay flue liners. I know I can use the cinder blocks for my base, and I was thinking about using the flue liners as the cooking surface of the oven (cutting the flue liners into flat sheets of clay). Is clay flue liner a good substitute for fire bricks? The flue liner is too big as an oven flue (it is 12" square).

Thanks,
Dan

[UtahBeehiver]

I am going the make the assumption the clay flue liner can handle direct contact with a flame so as far as that goes it "may" work. The main issue is the thickness of the flue tiles, typically you need at least a 2-3" of dense refractory material, ie bricks or brick tiles, to have enough thermal mass in the floor for cooking. Too thin and the BTUs will not stay in the floor. When you say 12" square, is that OD or ID, A rectangle or square flue is not as effective as a round flue. You do not say what size oven you are building, 32-36" ID oven requires a 6" round ID vent, 8" ID greater than 36". A 12" OD clay flue may work for a greater than 36" oven since ID may be around 10"+- and being rectangular or square.

[DanR]

I am going the make the assumption the clay flue liner can handle direct contact with a flame so as far as that goes it "may" work. The main issue is the thickness of the flue tiles, typically you need at least a 2-3" of dense refractory material, ie bricks or brick tiles, to have enough thermal mass in the floor for cooking. Too thin and the BTUs will not stay in the floor. When you say 12" square, is that OD or ID, A rectangle or square flue is not as effective as a round flue. You do not say what size oven you are building, 32-36" ID oven requires a 6" round ID vent, 8" ID greater than 36". A 12" OD clay flue may work for a greater than 36" oven since ID may be around 10"+- and being rectangular or square.

Thanks,
I looked into the behavior of the clay when directly exposed to flame. In a simulated chimney fire the clay cracked. Here is the video: https://www.youtube.com/watch?v=bxOkwQyY-2w

I may use firebricks instead.

I will build a 36"

Thanks!
Dan

[UtahBeehiver]

I think fire bricks will serve you better anyway.

[DanR]

I am collecting things from other build threads and putting them here so I remember them. I found this from Russell:
As far as insulation, it depends on exactly how you will use your oven. 2" of CaSi in the minimum amount of floor insulation, you can cook pizzas and have enough residual heat to use the oven the next day for roasting or baking. If you are planning on extensive bread making you will need more insulation and thermal mass (floor and dome). If you want to extend your residual heat then additional floor and dome insulation will be required. Another inch or two of CaSi would be great if the budget allows, an alternative is to pour a perlite or vermeculite/cement (5-1 ratio) first then lay the CaSi board on. Most important, make sure the floor insulation extends under the dome wall.

So, I will use 4" of FB Board underneath.

[WarEagle90]

Dan, that is a wise decision. When it comes to insulation, if in doubt, add more. There is a point of diminishing returns, but having too much insulation is not going to hurt anything.

[RandyJ]

I did 4" of calsill on my build , and if i ever do another i would probably do at leat that or maybe even 6".

Randy