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Old 11-21-2006, 12:41 PM
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I am trying to find the best quality firebricks and was wondering what the difference is between low-med-high duty? I am looking at a brick from the thermal ceramics site which is the closest match to the forno bravo formula

it is a high strength brick so i hope its ok but the formula is the closest match, so I think I can build a nice quality oven. Also, if I want to keep a nice balance should the floor be made of bricks with the same characteristics as I would rather use tiles for the floor, probably 2.5 - 3 inches. I know this is pretty technical but would love to hear an informative response. Thanks very much!

thermal ceramics formula:

Al2O3 38.8
Si02 47.8
Fe2O3 0.4
TiO2 1.6
CaO 10.9
MgO 0.2
Na2O and K2O 0.3

140 modules of rupture
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  #2  
Old 11-21-2006, 01:38 PM
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Firebricks are made of clay and an aluminum compound that is a by-product of aluminum manufacture. The higher alumina content means that they are resistant to higher temperatures, also that they are harder and more brittle. Low duty firebricks are made for fireplaces where wood is burned in open hearths. That's what we're doing is a brick oven, and that's the most we need for this application.

Higher duty firebricks are more expensive, and more difficult to work with.
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Old 11-21-2006, 01:50 PM
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That sounds right. The brick ovens and precast refractory ovens Forno Bravo works with are all around the 30% alumina mark. The Artigiano builder looked straight at me once, and said "we're cooking food here, not melting metal."

If you can find a great buy on some higher alumina bricks, that's OK, but I would not recommend specifcally looking for them.

My experience is that you can use the same material for the dome and floor. It seems like a happy coincidence that a basic firebrick on its side is right for your cooking floor (other than the joints).
James
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Old 11-22-2006, 12:42 AM
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Thanks for the info guys! Would bricks of this alumina content be a damper on performance? or do you think this formula is ok? Also, when I look at commercial ovens that aren't pre-cast, I see that they always use bricks for the dome and tiles for floor (I think usually 12" x 12" tiles). I assume the reason for this would be to cut down on joints. I was also am wondering what thickness the floor should be as tiles come in different sizes and thickness. I was thinking about a 3 inch tile thickness if the bricks in the dome are 4.5 inch thick since there is going to be a slab with the center lower portion filled with vermiculite insulation and the refractory concrete on top of the vermiculite concrete which will take up some thermal mass. About 2.5 inches refractory concrete cladding around the dome and about 4 inches vermiculite insulation between the oven and outer walls. I am thinking about a 50 inch diameter and a 17 inch dome height. I am planning on building it with an aggressive curve and a flat cuppola (neaopiltan style). Also thinking about a door width of 21 inches and a height of about 11.
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Old 11-23-2006, 06:36 AM
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Quote:
Originally Posted by artigiano
Thanks for the info guys! Would bricks of this alumina content be a damper on performance? or do you think this formula is ok?
There's nothing wrong with using higher duty bricks. It's just the expense and the difficulty of cutting that argues against it.

Quote:
Also, when I look at commercial ovens that aren't pre-cast, I see that they always use bricks for the dome and tiles for floor (I think usually 12" x 12" tiles). I assume the reason for this would be to cut down on joints.
Again, refractory tiles are expensive. They cost three or four times what firebrick costs. Remember, you're talking to home builders here. To some of us, the difference of a couple of hundred dollars in material costs is a major problem.

Quote:
I was also am wondering what thickness the floor should be as tiles come in different sizes and thickness. I was thinking about a 3 inch tile thickness if the bricks in the dome are 4.5 inch thick since there is going to be a slab with the center lower portion filled with vermiculite insulation and the refractory concrete on top of the vermiculite concrete which will take up some thermal mass.
Three inch thick is a lot of refractory, and if I read you right, you plan to put a refractory slab between this and the insulation. One of the chronic problems of home pizza ovens that only get fired up on the weekend is getting the floor hot enough to do real neapolitan pizza. The current thinking is that 2 1/4 inch firebrick floor directly on top of a high-tech insulation board like super-isol is the best bet for getting the heat we need.


Quote:
About 2.5 inches refractory concrete cladding around the dome and about 4 inches vermiculite insulation between the oven and outer walls. I am thinking about a 50 inch diameter and a 17 inch dome height. I am planning on building it with an aggressive curve and a flat cuppola (neaopiltan style).
You are planning on building a really large, really thick oven. Most home oven builders make a spherical dome, and for a good reason. Spheres are strong, and self supporting. They are forgiving of mortar or geometry problems. The low dome neapolitan oven exerts a LOT of force to the side. There's a reason for that concrete cladding, it's one way to constrain the horizontal forces on the dome. For most commercial builders, I understand that additional supports, in the form of side buttresses are also needed.

What you are describing is a commercial pizzaria oven, that's fired all day every day, all year long. It doesn't matter so much to these operators that there is a lot of excesses thermal mass, since it's pretty much kept hot all the time. If you were trying to fire a monster like that up for occasional use you would find you'd be burning a lot of wood to get it up to temperature, and maybe not succeeding.

Quote:
Also thinking about a door width of 21 inches and a height of about 11.
That door opening seems a little low, but it is a low dome oven. It's clear you aren't planning to bake your Thanksgiving turkey in it.

Good luck with your project.
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Old 11-23-2006, 09:23 PM
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Quote:
I am thinking about a 50 inch diameter and a 17 inch dome height.
I have a Casa 110, partially because it was what was available when I purchasaed it from Forno Bravo. There are times when I think that it is huge and it has a 43 inside diameter. Fifty inches sounds way to large to me for a home oven.

J W
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