#11  
Old 03-08-2007, 07:26 AM
james's Avatar
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Default Re: Splits in the hearth..

Hey all,

I like the idea of using 12"x12"x2" tiles. They will have fewer seams than a standard firebrick floor, and the 2" of thickness will be fine. I don't think you need to go to two splits. I think Maver has it right when he says that a modern pizza oven has only two components: thermal mass that asborbs heat and insulation that blocks it. The design philosophy is that the entire thermal mass of the oven is fully heated each time you cook. If your mass is too thick, and the inside of the oven is hot and the outside edge is still cool, then heat will be moving away from the inside of the oven -- while you are trying to cook. Not a good thing.

I try to remember that there are two reasons you might want to insulate something. First, to keep heat where you want it, and second, to stop heat from getting where you don't want it. They are very different. Pizza ovens are based on the first principle. You want to keep heat inside the oven, so it doesn't rapidly cool down when you are cooking. On the other hand, if your goal was to keep heat from reach the outside of the enclosure, you could insulate differently. You could wrap your oven in 10" of concrete. The concrete would suck the heat out of the oven, but it would also stop it from reaching the outside of the enclosure. That would be a very bad pizza oven , but it shows how important it is to use efficient insulation and the right amount of mass.

Take a look at the Modena design. It's so simple. Good proporations, efficient refractory and state-of-the-art insulation. That's it. One layer of refractory in the oven and a single type of insulation (lots of it) above and below.

http://www.fornobravo.com/commercial..._install1.html

I am definitely not a scientist, but the guy who designed the Modena is. He has designed pizza ovens, furnaces, kilns and ovens that fire glazed tiles, and he has consulted on large industrial projects, and even with another pizza oven company before he decided to make pizza ovens. Talking with him has really helped me.

I hope this helps.
James
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  #12  
Old 03-08-2007, 07:56 AM
Marcel's Avatar
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Default Re: Splits in the hearth..

Johnrbek wrote: "Was on the phone with a refractory supplier down here and he said it would be a good idea to double up on a the brick in the hearth and put it in running bond so that seams overlap..." ...."I imagine you could also do 2 reverse herrring bones as well.."

(M) Ever since 2005, when I introduced the idea of laying the herring bone 45 degrees on the bias, I've seen that the majority of builders use that layout for their hearth floor and have read no complaints about snagging a brick.

(M) My hypothesis was that by turning the herring bone pattern there would be the least likelihood of a peel catching on an brick edge because no bricks would be opposing the thrust of the peel. I guess you could "reverse" the 2nd layer if you wanted to overlap the joints.

(M) Here follow some images to illustrate my twisted mind set:



IMG]http://i14.photobucket.com/albums/a318/marceld/BRICKherringbone.jpg[/IMG]



Ciao,

Marcel
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  #13  
Old 03-08-2007, 12:32 PM
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Default Re: Splits in the hearth..

Originally Posted by johnrbek
we want to impede heat transfer by overlapping these seams.. that way the heat from the fire stays in the "conductor" layer(s) and doesn't get lost as easily into the "insulation" layer (through the seams). I do think however, that there has to be some inefficiency in conduction created by the minute air layer introduced by the second splits layer. Significant enough to affect heat up times? No idea.

Marcel: Here's where I think you and I are looking at it differently, JB. I would direct heat from my oven chamber through to the outer layers of my firebrick (right up against the insulation, perhaps with copper heat pipes?) if it were practical. Why? To improve heat up time (reducing wood use). As you fire the oven, the surface of the firebrick begins to heat but the conductive effect is to suck that heat through to the cooler brick close to the insulation. I didn't build my oven with thermocouples, but you can read Aravelo's experience with observing hearth surface temperatures and the time it takes to thoroughly saturate the bricks with heat


Marcel, I don't think we're in disagreement on that point at all. I agree with you, the objective is to heat soak those firebricks completely at the highest temp possible as quickly as possible. My point above was addressing a comment Maver made and was more about use the overlapping to impead heat from having a quicker path to the insulation through the seams. My understanding of what Doug at Atlantic Firebrick said was that you want the heat in the brick, not heading down cracks to the insulation layer. That was all I was saying there.

I think we've had some interesting discussion on the topic, so I'm happy to leave it at that if you guys are. My point with the topic was not to turn the world upside down or anything, just to relay some interesting (and different) information here. I get the sense some of the folks don't want to hear anything different from what they've been doing or what they've been told. I don't purport to be right here, just raise a different point of view from someone who appeared to be qualified to comment on the matter.

For what it's worth, I'll be laying my brick hearth next week. It will more than likely be in a single layer and in the same herringbone design you did yours in.

Regards,

JB
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  #14  
Old 03-08-2007, 01:26 PM
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Default Re: Splits in the hearth..

Quote:
Originally Posted by johnrbek View Post
My point with the topic was not to turn the world upside down or anything, just to relay some interesting (and different) information here. I get the sense some of the folks don't want to hear anything different from what they've been doing or what they've been told. I don't purport to be right here, just raise a different point of view from someone who appeared to be qualified to comment on the matter.
I think that because I wrote my reply in haste, it may seem that I'm in the camp of "we don't want any innovation around here". Nothing could be further than the truth. It's just that some innovations make more sense than others. Anyone who's built their dome, walking on the heath floor, and feeling it creak underfoot is going to want it built with the biggest, most solid pieces of refractory that the builder can afford.

As for me, I love to see people try different approaches, particularly if they come back and tell how they work. I'd even like to see someone actually build that smoker/grill vented through a domed oven idea that keeps popping up.
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  #15  
Old 03-08-2007, 02:16 PM
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Default Re: Splits in the hearth..

Thanks for the follow up Dmun... appreciate your response...

I said I was done with this one, but I just could help following up on this one point:

In James post above: Take a look at the Modena design. It's so simple. Good proporations, efficient refractory and state-of-the-art insulation. That's it. One layer of refractory in the oven and a single type of insulation (lots of it) above and below.

I agree on the design and proportions and efficiency etc.... It's a way cool oven and if I could afford one, I'd have gone that way in a heart beat!!

However, theres a point or two to clarify... the insulation actually isn't one type.. it's really three: insulating brick, vermiculite, and a bit of air in the gap he created between the 2 layers with the vermic residue... And, the two insulating brick layers are overlapping! Looks like at least the in the case insulation, there is a case to be made for overlapping seams... Also, the cooking floor is a single solid cast refractory piece. No seams to worry about in this case in the case of the hearth floor...

I think it would be interesting to see what your Modena manufacturer would say about Doug's idea... If you think it's appropriate, maybe you could run it by him next time you've got him on the horn...

Later.

JB

Last edited by johnrbek; 03-08-2007 at 02:19 PM. Reason: update
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  #16  
Old 03-09-2007, 08:58 AM
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Default Re: Splits in the hearth..

Quote:
Originally Posted by johnrbek View Post
I think we've had some interesting discussion on the topic, so I'm happy to leave it at that if you guys are. My point with the topic was not to turn the world upside down or anything, just to relay some interesting (and different) information here. I get the sense some of the folks don't want to hear anything different from what they've been doing or what they've been told. I don't purport to be right here, just raise a different point of view from someone who appeared to be qualified to comment on the matter.
JB, please allow us some leeway to ramble as we discuss things on this forum. I appreciate your ideas and am earnestly interested in your feedback, especially as you build your low dome (which as best I can tell is uncharted territory in home ovens). There is not a 'one way' to make a brick oven. With the overlapping hearth component idea there are pros and cons, but until someone is reporting from experience we're just kicking around ideas (which I think is fun). If I was long winded in my discussion about this it was not because I have any passion against the idea you brought to the forum, just a passion for these ovens and the ideas behind their performance.

Please keep it coming.

Marc
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  #17  
Old 03-09-2007, 10:33 AM
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Default Re: Splits in the hearth..

Quote:
Originally Posted by maver View Post
as you build your low dome (which as best I can tell is uncharted territory in home ovens)
Maybe not totally uncharted...
Kiwipete made a 36" oven with a 15" interior height
http://www.fornobravo.com/forum/f21/...-oven-302.html (Kiwi pete's oven)
http://www.fornobravo.com/forum/f8/k...oven-321.html\ (Kiwi pete'soven)

Kiwipete also inspired my cast vent, which I believe JB is goint to use...

Drake
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  #18  
Old 03-09-2007, 03:15 PM
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Default Re: Splits in the hearth..

I made our oven floor out of 12 by 12 by 2 inch tiles we procured for free by having the Penthouse Pet of the year interview the owner of a local pizza oven manufacturer. He gave us a bunch of tile offcuts which we used as an additional thermal layer before laying the full tiles on top. This all sits on 2 inches of calcium silicate insulation board.. Does anyone think I might have too much thermal mass in the floor? I added two rings to the dome in the last two days.. First two days I've hed to myself in two months..
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  #19  
Old 03-09-2007, 03:25 PM
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Default Re: Splits in the hearth..

Hey Nick,
Can I check this again? Your floor is the 12x12x2 tiles that you scored. Did you do two layers, where you have 4" cooking floor mass set on 2" of calcium silicate insulation? Is that right? I don't think it's a problem, but you might not have had to add the extra mass. My (very bad) memory was that those tiles were thinner than 2". Either way, you're fine.

Hope all is well on the home front.
James
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  #20  
Old 03-09-2007, 04:08 PM
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Default Re: Splits in the hearth..

Nick,

Yer a dog, bro. Penthouse Pet of the Year, indeed. You did score, no doubt about it.

Don't think you're in any trouble in the mass department. Fire up might be slightly longer, but not much. Then again, you'll have all that heat for the breads you WILL be baking. Right?

Jim
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