#1  
Old 08-24-2005, 05:12 PM
james's Avatar
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Default Island Hearth

Island hearth.

I am installing a new Forno Bravo refractory oven here in Healdsburg, and will be doing the Island hearth. The hearth is 7 1/2", with a 3 1/2 (+/-) concrete support layer, 2" vermiculite layer (+/-), and either a 2 1/2" or 1 1/2" thermal layer (still deciding). I am going to use firebrick for the thermal layer, and surround it with vermiculite concrete on the sides. My hope is that it will heat up quickly and do a good job of heat storage for the cooking floor, without the risk of wicking heat down and sideways -- away from the cooking floor. It should be more efficient that concrete, and doesn't cost too much more. I will mortar the FB Casa oven floor directly to the firebricks.

I'm taking photos, and will let you know how it goes -- and later, how it cooks.

James
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Old 08-24-2005, 08:51 PM
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Default Island Hearth photos will be appreciated

Dear James,

Congratulations on your 1,000th posting to the Forum.

I am looking forward to seeing the photos of your next installation in Healdsburg. I once stayed in a great BnB there where the hostess offered Finish Pancake. I don't think she cooked it in a pizza oven but it was great!

A 7-1/2" hearth is pretty deep so I guess this will be something of a prototype. Good luck on the installation.

Marcel
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  #3  
Old 08-28-2005, 07:58 AM
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Default Hearth forms ON or AROUND the top of block wall stand?

(M) I see that Jim H.and James placed their wooden forms OUTSIDE the hearth stand concrete blocks and secured them against concrete "blow-out" with cargo straps.

(M) Jim, did you use 2"x8" ? 2"x10" ? as at least 1 or 2 inches of your forms seem to extend below the outside of the concrete blocks? ____

================================================== ===

(M) I also see that jcdun?, from South Africa, placed his wooden forms ON the top of the hearth stand concrete blocks.

(M) I am planning on enclosing the "igloo" dome oven with a basic house facade made of cement board. The advantage as I see the house facade is that I can pour Perlite around and, most importantly, over the top of the igloo where the rising heat is most quickly lost.

(M) If I were to use the jcdun? method of setting the forms for the hearth pour ON the concrete blocks, and if I were to make those forms of 1/2" or perhaps 3/4" plywood, I would, after removing the plywood, have a ledge on which to rest my 1/2" cement board "house" walls. Please comment on this feasibility ____

Thanks,

Marcel
marceld@efn.org
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Old 08-28-2005, 10:22 AM
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Here are the photos for the Island Hearth. I used a 2"x8" to frame the hearth, and it did not need any straps, or cross bracing. I filled the 7 1/2" space as follows:

3 1/2" concrete with rebar in the bottom
2 3/4" vermiculite concrete
1 1/4" fire brick split

This gives me 3 1/4" high heat thermal mass for the cooking floor, fully insulatated on the bottom and sides. I am pretty excited about the thermal design, and will let the group know how the oven floor performs.

I learned a couple of things:

1. It does take longer to do the Island hearth, but it wasn't huge, so for many builders it should be worth the effort (assuming my oven cooks great).

2. The cost was a little higher. I used 40 fire bricks for the "island" which will cost more than the concrete you could use for the thermal layer. Again, we will see if the performance is worth the expense.

3. I set my firebricks in the wet vermiculite concrete, and tapped it level, and filled the sides. You don't have to do that. Thinking back, you could pour the vermiculite layer to level, and let it dry. You would then set the firebricks on top, and pour loose vermiculite around the "island" after the top walls were constructed.

Photos attached.

James
Attached Thumbnails
Island Hearth-foundation_480.jpg   Island Hearth-stand1_480.jpg   Island Hearth-stand3_480.jpg   Island Hearth-hearth1_480.jpg   Island Hearth-hearth2_480.jpg  

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  #5  
Old 08-28-2005, 10:25 AM
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Default The rest of the photos

One more thing. We set the form for the Island Hearth" at the height of the block stand. The form was held in place with a 2"x4".

Here are the next photos.

James
Attached Thumbnails
Island Hearth-hearth3_480.jpg   Island Hearth-hearth4_480.jpg  
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Old 08-28-2005, 12:13 PM
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Default One more photo

Here is the support I used under for bottom form (3/4" plywood from previous job). I simple brace to keep the form stable, and easily knocked out.

James
Attached Thumbnails
Island Hearth-hearth5_480.jpg  
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Old 08-29-2005, 09:47 AM
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This looks really nice. We poured our hearth just over a week ago and we did the island hearth with concrete. I used flashing screwed to a cross of wood for the island and relied on the concrete to form the circle.

It came out pretty good, but we ran out of cement to put a nice finish on the surround. *sigh*

This actually gives solidity to another idea I was having, which is to pour 2 inches more perlite around my brick hearth to insulate it and hold it in place. I think I'll go for it since the perlite/portland mix is so easy to work with..

But first, I have retaining walls to place around and below the oven to hold back the dirt and winter rain.

Tarik
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