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Jack Chastain 10-26-2006 08:58 PM

Placement of fire brick on cooking floor
What will happen if the firebrick is placed with it's 4 1/2" side on the cooking floor, or on edge with it's 2 1/2" side on the cooking floor? The cooking floor will have 4 inches of a perlite/cement mix under the brick, and reinforced concrete under the perlite mix. The placement of the brick on it's flat side will provide less material to absorb the heat, but what effect would that have on building up and holding heat for pizza? Conversley what effect would it have when baking bread?

dmun 10-27-2006 05:53 AM

Having a cooking floor that is twice as thick will mean that the oven will heat up more slowly, and use more fuel, conversly it will hold heat longer and bake more batches of bread.

By the way, if you want more thermal mass on the floor, you don't have to use twice the number of fire bricks. A search for "island hearth" will show you a way to bury a slug of plain concrete in your insulating concrete layer to increase your thermal mass if that's what you want to do.

On the other hand, a herringbone pattern floor with the bricks on edge is a really cool look, so if you are doing it for aesthetic reasons, go right ahead.

maver 10-27-2006 08:38 AM

my only concern with bricks on edge would be increased seams - I think the island hearth is a more useful way to build mass. I placed my hearth with a herringbone pattern at 45 degree angle to my entrance which reduces the chance of catching a seam but it still happens (usually when raking coals out). Beyond the issue of interrupting delivery or removal of pizza/bread/ashes/coals you also need to be concerned with grinding the seams and introducing grit into the oven to later get in your food.

james 10-27-2006 09:08 AM

I think the idea that a 4 1/2" cooking floor is "better for baking bread" is missing the point. It is better for baking commercial quanities of bread, but it's not better for bread.

For some context, I want to note that the high-end commerical Italian-made pizza oven we sell has a 2 3/4" thick cooking floor set directly on solid-state insulating tiles. There are restaurants all over the world that use that type of oven to cook pizza and other dishes all night, then come in the next morning to bake enough bread to serve the restaurant that day from the retained heat.

When we say the thicker cooking floor is "better for bread," that means 3+ batches, loaded with 30+ loaves each time -- or 100 or more loaves of bread from a single firing. To me, that describes commercial micro-bakery quantities of bread -- as Jim does with his great bakery. That does not describe the bread baking that a home owner, or even a restaurant, would ever want to do.

If you want to bake 25+ loaves of bread a day -- which means you are giving away a lot of bread to your neighbors, the cooking floor with the bricks on their flat sides, at about 2 1/2" is perfect.

On the flip side, going from a 2 1/2" cooking floor to a 4 1/2" cooking floor is a big move. Keeping the cooking floor at high heat for pizza is one of the bigger challenges you face as an oven owner. I get requests for tips on how to keep the cooking floor hot all the time. By adding the extra mass, you are making the job of keeping the floor hot all the more difficult. You have to fire the oven longer to completely fill the "mass" with heat -- otherwise the cooler outer part of the cooking floor will wick heat away from the inside of the oven. And you have to burn more wood to keep the floor from cooling down.

Sorry I jumped up and down on this, but I sometimes worry that folks read the Bread Builders book, and really get the wrong end of the stick. It can be very misleading -- and you can end up with an oven that does not do what you want. Which would not be good.

Hope this help!

DrakeRemoray 10-27-2006 10:08 AM

I agree with James, read my post on 3 days of cookingI had plenty of retained heat and my bricks are setup to make a 2 1/2 inch thick floor set directly on insulating concrete.


Jack Chastain 10-27-2006 01:25 PM

Placement of firebrick
Thanks one and all! My brick will be flat! Jack

CanuckJim 10-28-2006 08:35 AM

Brick Orientation

I agree entirely with you, Drake and Maver on the question of hearth brick orientation. For my purposes as a micro-bakery owner, it was preferable to set the hearth bricks on edge for precisely the reasons you all mention. However, heating such high mass takes time and fuel for multiple batch bread baking. For pizza and occasional bread, the flat approach makes much more sense from a speed perspective and also to keep that hearth hot, hot, hot.


Alf 10-29-2006 10:55 AM

There seems to be some confusion here as what thermal mass is or does to the cooking / baking ability of an oven. The thermal mass of a wood-fired oven performs two operations.

1 It equalises, balances and spreads out the heat generated by the fire within the oven.
2 It stores heat from the burning wood to be used later for baking.

More thermal mass wont create a hotter oven, quite the reverse in fact, as James and Jim pointed out the oven will have difficulty in getting to real pizza heat with out using a lot of time and fuel. For domestic ovens keep the thermal mass low you will get a quick heat up and a hot oven for your weekend use.

In my opinion there are two areas where low mass in a domestic oven may be a problem.

1 if you want to bake large sourdough breads, they generally require a lot of hearth heat to bake the breads and give them that special taste.

2 long slow cooking / baking of large joints of meat or turkeys etc.

For the odd occasion when a higher floor mass may help just add one or two pizza stones or firebricks as you are firing the oven. Then bake or slow roast / cook your desired dish on the extra mass of the oven floor and pizza stone / firebricks.


CanuckJim 10-29-2006 01:40 PM


Very good clarification of the issue, with a very good and simple suggestion of how to increase mass for special, occasional requirements. Now, if I could only figure out how to reduce the mass of my oven for pizza :D .


carioca 10-29-2006 08:39 PM


Originally Posted by Alf
1 if you want to bake large sourdough breads, they generally require a lot of hearth heat to bake the breads and give them that special taste.

Thanks for the explanation, mate! But since we usually bake two big sourdough loaves twice a week, sometimes three times now that we have lazy daughters in the neigbourhood :-), that seems to mean WE should go for the extra mass?!

My supplier has offered to include 50 mm thick hearth tiles in the order, since the're out of the 38 mm ones - I suppose that helps?

(Timber's not a problem on our lot: I've felled a few eucalypts this year, and there's always but always enough fallen timber anyway...)

Cheers, and thanks again for giving us novices such a good forum to get some knowledge!


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