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Old 10-04-2006, 04:20 AM
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One of the things that I find interesting about brick ovens is the range of options that exist that could be called a "brick oven", or "wood-fired oven". You can literally stack up a bunch of bricks, or pour clay or concrete around a form, fire it and cook bread and pizza. Cro Magnon man had wood fired ovens. At the other end of the spectrum you choose oven chambers specifically designed for baking Italian pizza and surround them with very efficient space-age insulators. And there are many points in between. You can install an oven on a 6" non-insulated concrete slab, and it will cook.

The good part of this is that as a builder, you can pick where you want to be on the spectrum -- based on how much effort you want to put into it, money, how often you will use it, etc.

Clearly, a well-insulated oven made using a specially built oven chamber (shameless plug for Forno Bravo), will cook a lot better -- and as the chef, you will enjoy using it a lot more. It will heat up fast, it will hold heat better, it will hold high heat better, it will use less wood -- so that you can make great Italian pizza (or NY, or Sicilian), and bake bread and roast a turkey without the oven giving up on you. If you are a real pizza lover, you need a high-end oven.

Can you install a modular oven with one page of refractory mortar and three bags of Vermiculite? Yes. But if you can try a little harder, you will be well rewarded. If you can't, having a less sophisticated oven is a lot better than not having an oven.
Helpful?
James
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  #12  
Old 10-05-2006, 12:09 AM
Peasant
 
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Default bricks again

I got the price for the insolation bricks, 80 cents apiece, they are white-ish and 9"x4.5"x3". I think I might go with these for the base with say an inch or 2" of vermiculite between the Insol bricks and the fire bricks. The fireclay bricks are also 80 cents and they only have med duty. I understand medium bricks will get hotter, so would it be wise to increase the insulation? Any suggestions for the size of the base? I would like to build a 36" or 38" oven
Thanks again
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  #13  
Old 10-05-2006, 02:30 AM
Peasant
 
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Default bricks

The insolation bricks are composed of 15%-Alumina, 51%-Silica, 29% Lime and 0.5% Iron Oxide. with a thermal conductivity of .16 W/m.K at 800 deg C. Does this mean anything to anyone? I would like to know if this would be better than vermiculite for my base or if I should just go with the vermiculite. The cost of the bricks seems reasonable.
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  #14  
Old 10-05-2006, 06:13 AM
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I will ask my thermal engineer contact -- the one with the simulation software. I'm not sure how fast he will back, but I'll ask.
James
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  #15  
Old 10-05-2006, 06:32 AM
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Default thermal conductivity

Vermiculite concrete, per a previous post here by Jengineer has a thermal conductivity of 0.69-0.73. Super isol at 750F has a thermal conductivity of 0.55. Lower is better. If the insulation bricks are affordable then go for it. The K value for insulating fire bricks stays fairly flat through the usual temperature range of a pizza oven (there's a graph here http://www.ibar.com.br/index_eng.html). Their insulating firebricks have thermal conductivity values of 0.2-0.25 for low density and 0.4 for higher density brick but their units are kcal/m h C, multiply your bricks' K by 1.163 to convert ( http://www.engineeringtoolbox.com/un...ter-d_185.html ).

The same source Jengineer used for the thermal conductivity of vemiculite concrete lists perlite concrete as having a thermal conductivity of 0.58 ( http://www.schundler.com/perlcon.htm ). Strangely enough, dry sand has a lower K value, 0.35, although if it absorbs lots of moisture it is worse than concrete (which has K value of 0.9-2) going up to 2.7.

I'm happy with my oven's thermal performance for home use with just perlite concrete under the bricks - I have never been able to feel heat through the concrete support under the perlite concrete and my oven gets hot and stays hot for making pizza and bread. I have 3 inches of perlite concrete. I don't see any reason you would need to place insulating bricks over a layer of vermiculite concrete.
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  #16  
Old 10-05-2006, 07:46 AM
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Just to get back to the original question

“I am planning on building a pizza oven soon. Can you use insulation bricks under the fire bricks in the Hearth. I live in Thailand and am having difficulty finding vermiculite or Perlite, Isol, Laowool, Insulfrax etc... I have located firebricks, morter and industrial insulation bricks. I have read that Pumice may be used as an alternative. Has anyone tried this”

Why not build the oven using the insulation firebricks – Ok its not whats recommended but remember ovens have been built from all sorts of different materials in the past and they worked. The main problem with the old ovens was insulation. I've taken to bits and repaired ovens and furnaces that have been built with insulation firebricks and they all seemed to work ok. So, if resources are scarce in Thailand just use the insulation firebricks on their ends and at full length. Then use any rockwool type insulation that can be found from ventilation engineers etc and your final finish coat.

OK it wont be quite the full monty pizza oven, but once you get the hang of the way the oven cooks it will be great.

Alf

Last edited by Alf; 10-05-2006 at 10:13 AM.
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  #17  
Old 10-05-2006, 01:15 PM
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"I've taken to bits and repaired ovens and furnaces that have been built with insulation firebricks and they all seemed to work ok." -Alf

So how would building an entire oven out of insulating firebricks relate to the thermal mass design principle? My understanding was the firebricks or the refractory modules such as Fornobravo sells are able to store and then radiate heat to keep the oven temperature even and allow retained heat baking after the coals are raked out. Does an oven made of insulating firebrick heat up faster? Is it harder to maintain an even temperature? Are people able to do retained heat baking? Curious.
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  #18  
Old 10-05-2006, 01:43 PM
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Default Good question

Maver,

You have this exactly right. Every brick oven is comprised of two elements -- those that absorb and hold heat (a thermal layer) for cooking and those that stop heat (an insulating layer), and keep it inside the oven. I'm sure Alf will answer this as well, but I think his comments were relative to the merits of the insulating layer. An oven made from all insulating material would never get hot, it would just vent hot air out the front door.

Historically, the thermal layers were clay and the insulators were sand, pumice, expanded clay, and ground glass. Then, modern science took over, and today we have easy access to engineered refractories (a Forno Bravo oven), Insulfrax and SuperIsol (and vermiculite). The ovens heat up faster and insulators work much better. While, the basic design has not changed for 2,000 years, the materials changed in the past 5+ year. Ancient Rome meets NASA.

If you live in a place where you can't easily find Insulfrax of a Forno Bravo oven, the traditional materials work very well. Go for it. For everyone who can access the other materials, you have the best of both worlds.
James
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Last edited by james; 10-05-2006 at 01:49 PM.
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  #19  
Old 10-06-2006, 12:38 AM
Peasant
 
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OK thanks for all your input. If I understand this correctly the insolation bricks have excellant thermal Conductivity (very low at 0.16 w/mK). At 3" thick I think I will just dry stack them on my base, under my fire bricks. They are less than a dollar each so not very expensive. At this price would they be a better option than Vermiculite?
Thanks again
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  #20  
Old 10-06-2006, 06:58 AM
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Default better than vermiculite

They insulate better and are easier to handle - should be much better.
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