Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

[southpaw]

Hi all,

ill be building a 32" forno, and have a few Question concerning the thickness of the (Fire Bricks):

- How thick should the fire bricks be? (4.25" or 2.5")
- Is there a minimum thickness for the fire bricks?
- If you add more (fire bricks) thickness, is that considerd adding more thermal mass?
- If you increase the thickness it will take the oven longer to heat?

[wlively]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Hi all,

ill be building a 32" forno, and have a few Question concerning the thickness of the (Fire Bricks):

1. How thick should the fire bricks be? (4.25" or 2.5")
2. Is there a minimum thickness for the fire bricks?
3. If you add more (fire bricks) thickness, is that considerd adding more thermal mass?
4. If you increase the thickness it will take the oven longer to heat?

1. I don't think there is a right thickness. It is personal preference for use, pizza or bread, ease of building, ect. Mine is approx 4.40" from bottom to 2/3 up and the last third is 2.7" . I thought I had enough mass and wanted to lighten the top of the dome.

2. Don't know. Would imagine that if the insulation is done perfectly and completely, then maybe you could get away with 1-1.5 inches. But that would seem to increase the labor. 1/3 brick dome would be fine for pizza and small batch(household) bread. Again insulate, insulate, insulate.

3. Yes. You are adding mass that will draw away or soak up the heat form a higher temp environment and then give it back to a lower temp environment. You can think of it like a sponge, the bigger the sponge the more water it will hold.

4. Yes. More mass means more mass to have to heat up. Like a pasta pot of water, if you only put 2 inches of water in the bottom it will come to a boil rather quickly. If you fill it to the top it takes a long time.

Unfortunately, that is life and engineering, there are always trade-offs. A Ferrari is very fast, but is expensive, only carries two people and eats alot of fuel. A Prius (insert your favorite 4dr here) is not so fast, but for alot less carries four and uses alot less fuel. Not related to ovens I know, but you get the point. You need to decide what your mission is and then plan accordingly.

[Hendo]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

On the question of dome thickness, should one also take into account the stability of the structure? I?m thinking here of the catenary curve again, and the desirability of making sure the ?line of thrust? stays in the middle third of the dome.

This has been discussed previously, and there are some interesting diagrams and explanations at Auroville Earth Institute is a research, design and developing agency for vaulted structures, construction of various Vaults, Arches, Domes (VAD)..

Even with 4?? thick bricks, I don?t know that the ?line of thrust? will end up in the middle third of my 43? ID dome, but I haven?t heard of others falling down either! But knowing about this theory would certainly make me carefully consider going any thinner if I was starting again.

What do others think?

Paul.

[Dutchoven]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

I am with you Paul. Keep the structural stability in mind. Much easier to keep line of thrust in the middle third of 4.5 thick wall than that of a 2 inch wall. Wade's idea is very good though, one might even go as wide as 6 inches on the lower courses, 4.5 inches in the middle and 3 inches nearing the top. That would load the hauches of the dome and lighten the upper layers. Could use all the off cuts if one was careful even! It might even come to a cooking temperature a bit faster?! Hmmmm?
Best
Dutch

[wlively]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Good point Paul. When talking about thickness, in my mind I was thinking absolute thermal performance limits and was not considering structural.

[beardedbee]

granite slab for floor ???

i am in the research/ planning stage of building an oven for my back yard..i have access to a 4 foot x 4 foot 6 inch thick piece of polished granite would this be any good for the floor of a dome style oven i was thinking the smooth surface would be good for cooking ..would it stand up to the heat...would i still have to insulate under it ????

[Dutchoven]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Bee
I am very jealous!!! However I don't think granite would be a good idea for the floor as you may have some serious hot spots due to inconsistencies in the structure of the natural stone. Some ovens have used soapstone for the floor and they say it heats up quicker but, personally just a good medium duty firebrick is perfect and can be smoothed quite easily with a belt sander. Not to mention the fact that that pretty piece of stonewould be virtually invisible as the oven floor. I would suggest looking into getting it ripped in half by thickness and then you could have 8 feet of 3 inch thick granite counter on which to spin your pizzas.
Best
Dutch

[alex.g]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Sorry for bumping an old thread, but i think it would be better to have all in one.
Im in process of finding good firebricks locally (Slovakia), all i can find is about 2.5inch (6cm) bricks.. and those have no perfectly straight sides (like JM23 insulation bricks).
Simply not like this: https://picasaweb.google.com/lutz.hu...23702838639442

So i have two problems.. i can't imagine how to make a cooking floor out of my waved bricks.. there will be a lot of space between bricks. I cant grind sides, coz every single brick will be different then.

So i can get some plates made of fireclay (5cm x 20cm x 50cm) - Šamotový plát, rozmer 5 cm x 20 cm x 50 cm - kachliar.sk - eshop
those are pretty straight

so my question is, is 5cm thickness enough for cooking floor? (5cm is about 1.97inch).
Thank you

[SCChris]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Alex, use what you have. I think you'll be fine with 5cm, you'll have a bit less storage of heat, but you should be fine. If you're concerned about thermal mass, or find that you want more, you could double up on the floor, 2 x 5cm. Most of the No. American ovens are about 6cm thick on the floor..

Chris

[alex.g]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Thanks, maybe i will add 2cm plates underneath, to be sure
If.. should i just place those on top or mortar?

[SCChris]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Alex, My floor bricks just lie on the rigid insulation below. Given these plates are relatively flat, laying them, in 2 layers, without mortar should be fine. Over time the ash from the fires will work down and into the gaps and stabilize the floor structure. One point that is made over and over relates to the insulation of the oven. More insulation will give you more cooking time with less wood/fuel, the temperatures will be more stable for your cooking and baking.

Chris

[alex.g]

Re: Oven (Floor - Wall - Dome) Fire Bricks Thickness?!

Great
I'll do a photolog, for sure.

[jd22]

11 years later... a new question appears. I'm embarking on my own build and am running into some budgetary considerations. What does the FB hivemind think of using 6cm firebricks for the floor of the oven (with refractory bricks and cal-sil plates) and then 3cm bricks for the walls? Would it be preferable to maintain 6cm firebrick thickness throughout the entirety of the firebrick layer?

[david s]

The dome needs to be thicker than 3cm so it can hold enough heat without cooling too fast, as well as providing more thermal mass for retained heat cooking. Most cast ovens go for 5cm walls, some bigger ovens 7.5cm. Unfortunately if you try to build really thin walls in brick it will fail because there is insufficient strength in the narrow mortar joints. Brick walls for a house are not laid on edge for this reason. Hundreds of years have proven they need to be 10cm.wide at least.
A further problem with an oven is the uneven thermal expansion. The thinner the bricks the greater the stress on the mortar joints.

[Sixto]

I'm with David, even if you don't care about retained heat cooking, the amount of time you'll be spending building and using this oven are worth waiting until you can afford purchasing enough bricks for 6 cm walls. (mine are 11.4 cm or 4.5" thick). Have you looked for used Firebrick? I did, and I think I got a good deal on materials overall. Unfortunately, I've clocked about 30 hrs per week in June, July and August, cutting and mortaring all of that, so you could say that my learning curve, and labor investment are equal to, and will probably surpass my material costs, even at minimum wage of $15.00/hr.

Ugh, time for a beer, so what if it's before 5:00 p.m!

Cheers!