help 4.5 vs 9 inch bricks for the dome
Im planing to build a pompei type oven primarily for bread and I was planing to use 9" fire bricks for the dome untill I read the piece about too much thermal mass. What are the disadvantages of using 9 inch brick for the dome, what is the difference in firing time to get the oven to the proper temperature? How long does it take the 4.5" dome to reach it and what should I expecte if i use 9"? And what about thermal capacity, by reducing the size of the dome would I have enough heat to bake my bread?
Thank you for taking the time to read and answer my questions.
In Need of Assistance
How much bread?
In a way, I think it depends on how much bread you want to bake. If you want to do bake one batch of bread (20-30 loaves) from a single firing, then the standard Pompeii oven with 4 1/2" of dome will be right for you. It will fire in about an hour and easily hold enough heat for a batch of bread. You can also do that with a refractory oven.
A longer heat up time than that is not only a hassle, it costs real $ in fuel, and I think it is bad for the environment.
If your bread desires are more than that, or you are starting a commercial microbakery, you might think about the "mailbox" design. It is a rectangular barrel vault, with 4 1/2" of brick and 4-5" of additional concrete. It takes 3 hours to fire, but can bake 2-3 batches (75-odd) loaves from one firing.
some more questions
Yes, thank you very much James.
The oven is for domestic use and the plan is for a 42” diameter and 20”- 21” dome. I don’t have any specific cooking plans in mind, is going to be used occasionally and I was hopping for couple of cooking cycles maybe once for bread and the other for a roast with each firing. I have Alan Scott’s book with the plans for the barrel oven but I like the challenge of building a Pompeii type oven, after all it’s a “Hemi” oven.
The other think I was going to ask was about cladding, I didn’t see any specific information on the side, and do you use any on your oven? Do I need it? And if yes how much should I use.
Thanks again for your help
The standard 4 1/2" dome (1/2 a brick) is fine for being able to cook both a load of bread & a roast afterwards. I cook pizza at 700F (hearth temp), let the fire burn out and cook bread once it cools to 400ish. Then I'll throw in a roast to wrap it all up. Doing the bread gives it something to do while I wait for the oven to cool to roasting temps -- 325ish for turkey or pork, 250-275 for a long roasting prime rib.
I'll also cook roasts in the oven with a fire wrapped around the roasting pan (not from retained heat) so you've got lots of options with this. That's one of the reasons I made the 42" oven -- the Scott I built wasn't wide enough for fire in the oven cooking.
As for cladding, you don't clad the Pompeii. As you build the dome you "butter" it with mortar. You'll end up with about a 1/2" thick coating on the dome when you're done. This is sufficient for the oven and does not require a cladding layer like Alan's design (the cladding is for the extra thermal mass he designs for -- which allows for more loads of bread but requires substantially more heating time).
Sealer On The Dome
Jim and others,
I would like to seal the dome once completed, but I would not want to trap IN any moisture. How many firings do you think should take place before sealing the dome?
Go with James and Jim’s recommendations of a 4.5 - 5 inch oven shell. Using full 9 inch bricks on their ends is for much larger commercial ovens that will be fired every day for several baking’s. The key to the efficiency of these small round ovens for home use is the insulation you put under and around it.
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