Old 05-13-2006, 12:52 AM
Join Date: Oct 2005
Posts: 3
Exclamation re insulating hearth

I have been given some fire bricks out of a kiln. Is it possible to place these bricks on top of the cement stand ( SLAB) to use as an insulating hearth, and then place the normal fire bricks on them for the oven floor. The bricks are thicker than the ones recommended for the oven dom.This would save me some time as I live on a farm.

Any help or advice would be great.

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Old 05-13-2006, 01:52 AM
redbricknick's Avatar
Join Date: Apr 2006
Location: Los Angeles
Posts: 271
Default Who knows?

I don't really know, but I'm really interested to find out. It sounds like it could work really well though. What stage of your hearth slab are you at? I just said really too many times.
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Old 05-13-2006, 02:24 AM
Join Date: Oct 2005
Posts: 3
Default insulating hearth

I am at the planning stage, because i am on a farm i am restricted to a certain degree as to having materials delevired etc.. So i am trying to build the oven as
cost effective as a possible
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Old 05-13-2006, 05:33 AM
CanuckJim's Avatar
Il Pizzaiolo
Join Date: Jan 2006
Location: Prince Albert, Ontario, Canada
Posts: 1,480
Default Thicker


Thicker is always better, for heat retention in particular. I've got a very simple and cheap method for adding insulation below the hearth. Haven't got the pics together yet, but I will by next week, and I'll be posting them here. Trying to explain with words only wouldn't work very well.

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Old 05-13-2006, 06:09 AM
Fio Fio is offline
Join Date: Apr 2006
Location: Virginia
Posts: 166
Default Are those kiln bricks insulating or conductive?

My only observation is that if the underlayment of bricks conducts heat, it will such the heat from your oven floor and conduct it to the hearth slab, which will REALLY suck up the heat. You should try to build a thermal barrier. I am using Fiberfrax insulating board.
There is nothing quite so satisfying as drinking a cold beer, while tending a hot fire, in an oven that you built yourself, and making the best pizza that your friends have ever had.
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Old 05-13-2006, 01:04 PM
CanuckJim's Avatar
Il Pizzaiolo
Join Date: Jan 2006
Location: Prince Albert, Ontario, Canada
Posts: 1,480
Default Heat

Fio, Rocco,

I think we're at cross purposes here, probably because of the definition of terms. To retain heat, you want to heat your fire brick and let the heat be stored in the bricks AND slab. Below that, you have an insulation layer of some sort, the more efficient the better. The thickness of the hearth bricks and the thickness of the slab that contacts it both contribute to heat retention and heat equilibrium. Below that, you want to insulate, insulate, insulate. The method I mentioned has to do with adding more insulation even below the insulation you've already installed. Part of my confusion might have to do with the fact that my oven is an Alan Scott design for bread; yours, I assume, are primarily for pizzas. There are many differences, but heat management is not one of them. Let's clarify and then continue.

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Old 05-13-2006, 08:49 PM
Marcel's Avatar
Join Date: Aug 2005
Location: Oregon
Posts: 426
Default And also insulate the dome! Heat rises

Originally Posted by CanuckJim
Fio, Rocco,


Below that, you want to insulate, insulate, insulate.

(M) But when you insulate under your hearth bricks and slab, remember to also insulate your dome. Since heat rises you may be retarding heat loss even more by investing in dome insulation. Those of us who have built an enclosure for the dome often simply pour dry Perlite or Vermiculite over the dome. Others coat the dome with "Perlcrete", and some, such as I, even have a layer of aluminum foil between the dome bricks and the Perlcrete, and then only added dry Perlite.

(M) Those who choose not to build an enclosure typically apply a thick coat of Perlcrete to their dome bricks. Now also insulate under your hearth as Canuck Jim advises.


"Everything should be made as simple as possible, ...
but no simpler!" (Albert Einstein)
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Old 05-14-2006, 06:08 AM
jengineer's Avatar
Master Builder
Join Date: Aug 2005
Location: Garden-A, South California
Posts: 572
Default Insulate above or below

Present and Future Builders-

Pay close attention to CanuckJim words. He is describing a hearth that was originally in the Pompeii plans.

Make Bread All Day
Top down your have fire brick floor placed on a heat sink (reinforced concrete) and that is on insulating matrix (concrete and perlite or vermiculite). This method of the hearth gives a large thermal mass or heat sink that is ideal for long term bread baking as that is Jim's primary use.

Make 3 minute Pizaa and some bread
This past year a few/couple builders at the direction of the forum have flipped the order of the hearth. Top down you have the fire brick floor placed on an insulating matrix and under that you have your reinforced concrete. A derivative of that is to build an thermal island directly under the floor about 2 inches thick if you want extra thermal mass. It will take less time to get the floor fire bricks up to the heat they need to cook your pizzas, in the hours after your main cooking you still have time for a few loaves of bread or a roast.

You need to decide what your main cooking usage will be and build accordingly.
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