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Author Topic: A couple questions before I start my build !  (Read 472 times)

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Offline Elkaybay

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A couple questions before I start my build !
« on: May 19, 2018, 04:34:54 AM »
Hi everyone,

I have a couple remaining questions before I start building my Neapolitan oven (130cm diameter cooking surface, with Biscotto di Sorrento)

First question is about the insulation below the cooking surface, and around the dome.
Perlite appears to be a much better insulator than expanded clay, but it seems that most Neapolitan oven makers prefer to use a cement-expanded clay mix. It also seems that they use cement at a higher ratio than what was recommended many times in this forum (1/8).
Is it just about tradition? Price? Solidity? Weight? Where I live the expanded clay is much cheaper than perlite/vermiculite so I'm tempted to do it the 'traditional' way.

Second question. I can find low-medium duty firebricks with a 28%, 30% and 35% alumina content for building the dome. I understand that Ferrara uses bricks with an even lower alumina content so I'm tempted by the 28% ones (they are also the cheapest). How much of an impact has alumina content when building the dome? Thermal conductivity doesn't matter much, but I suppose that the heat retention will be different?

Thanks a lot!

Offline vtsteve

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Re: A couple questions before I start my build !
« Reply #1 on: May 19, 2018, 06:23:48 PM »
The Italian builders are, for the most part, building ovens that will be fired every day. So, the "insulation" under the floor also functions as thermal mass. It doesn't matter if it takes 10 hours from a cold start for the floor to stop wicking heat away, because it's never going to get cold. For less-than-constant use, a thinner floor with better insulation is the way to go.

That said, I built my oven with a 6.5" thickness of firebrick, on top of very good insulation -- 3" of cal-sil board and 4" of Foamglas. I bake a lot of bread, and the extra brick means that I need to start firing the day before, but I can bake 40 loaves of bread (or 20x18" pizzas) without refiring, and only lose about 100oF over the course of the bake.


Use the low-duty bricks. The high-duty are for blast furnaces, cement kilns, and other (chemically and thermally) extreme environments. If Neapolitan is your goal, plan for a biscotto floor.
In grams we trust.
My wood-fired NY thread: Pizza Thursday

Offline Elkaybay

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Re: A couple questions before I start my build !
« Reply #2 on: May 20, 2018, 02:39:56 AM »
Thank you very much for your answer!

I'll be firing my oven every day, so I'll then also go for the thicker insulation (20-25cm LECA-cement mix), then I will have a layer of firebricks (6cm)+sand (6cm)+salt (0.5-1cm) on top of which I'll place the biscotto.

The 6.5 inch firebrick layer you mention, is that under your oven floor?

On the firebricks, I'll then go for the lowest duty ones, 28% alumina. Good for me they are the cheapest :)

Have a great day!


The Italian builders are, for the most part, building ovens that will be fired every day. So, the "insulation" under the floor also functions as thermal mass. It doesn't matter if it takes 10 hours from a cold start for the floor to stop wicking heat away, because it's never going to get cold. For less-than-constant use, a thinner floor with better insulation is the way to go.

That said, I built my oven with a 6.5" thickness of firebrick, on top of very good insulation -- 3" of cal-sil board and 4" of Foamglas. I bake a lot of bread, and the extra brick means that I need to start firing the day before, but I can bake 40 loaves of bread (or 20x18" pizzas) without refiring, and only lose about 100oF over the course of the bake.


Use the low-duty bricks. The high-duty are for blast furnaces, cement kilns, and other (chemically and thermally) extreme environments. If Neapolitan is your goal, plan for a biscotto floor.
« Last Edit: May 20, 2018, 02:50:27 AM by Elkaybay »

Offline vtsteve

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  • Location: Vermont, USA
  • If my pizza is wrong, I don't want to be right!
Re: A couple questions before I start my build !
« Reply #3 on: May 20, 2018, 02:56:30 AM »

The 6.5 inch firebrick layer you mention, is that under your oven floor?



My floor has two stacked layers of firebrick; the lower layer is set on edge, 4.5" and the cooking surface is on flat, 2.25" (so actually 6.75" total).
In grams we trust.
My wood-fired NY thread: Pizza Thursday

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