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Author Topic: Minimum dome thickness  (Read 748 times)

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Offline LaLabbo

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Minimum dome thickness
« on: February 23, 2018, 03:37:18 AM »
I have a question to all the masons:

Whats the minimum stone thickness for a neapolitan dome with lets say 100cm diameter.
Given that it has a layer of reinforced mortar on top.

Thanks,
Labbo

Offline vtsteve

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Re: Minimum dome thickness
« Reply #1 on: February 23, 2018, 01:34:06 PM »
Do you mean for structural stability, when it's made of bricks in the traditional manner? You could go thinner with a cast shell, which is what you're  approximating with thin bricks and a mortar cap (except you can include steel fiber reinforcement in a casting). Some of the FGM ovens use thin brick facing on the inside of a casting.
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Offline Tscarborough

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Re: Minimum dome thickness
« Reply #2 on: February 25, 2018, 10:52:44 AM »
The dome thickness is a function of the specifications of the oven.  That is, there is no structural reason for any particular thickness, it is designed to do what you want it to do.  Fast heatup? Thinner.  Multiple  pizzas? Thicker.   Standard is 2-1/2" because that is the thickness of standard firebrick.

Offline vtsteve

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Re: Minimum dome thickness
« Reply #3 on: February 25, 2018, 01:24:34 PM »
The dome thickness is a function of the specifications of the oven.  That is, there is no structural reason for any particular thickness, it is designed to do what you want it to do.  Fast heatup? Thinner.  Multiple  pizzas? Thicker.   Standard is 2-1/2" because that is the thickness of standard firebrick.

I would have said 4.5" because half-bricks on end seems to be the most common.
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Offline Jon in Albany

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Re: Minimum dome thickness
« Reply #4 on: February 25, 2018, 01:42:32 PM »
I went with 3" thick in an attempt to balance heat up time and thermal mass. The 3 inches are heavily insulated. I don't have a door yet and just stack firebrick in front of the opening. They were warm to the touch 2 days after my last firing.

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Offline LaLabbo

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Re: Minimum dome thickness
« Reply #5 on: February 26, 2018, 04:14:48 AM »
Thank you very much!

Yes my main goal is to fasten up heat up times. First I thought about a steel dome, which would clearly have the fastest heat up time but since I have to do lagrge volumes that makes heat stability too bad. So a thin stone dome would be perfect for both, small volume events with fast heatup, and large volume events with a bit of mass and a large fire.

I wanted to go as this as 1.5", coverd with a mortar cap that is reinforced with a steel fibre.


Offline Jon in Albany

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Re: Minimum dome thickness
« Reply #6 on: February 26, 2018, 08:25:34 AM »


Thank you very much!

Yes my main goal is to fasten up heat up times. First I thought about a steel dome, which would clearly have the fastest heat up time but since I have to do lagrge volumes that makes heat stability too bad. So a thin stone dome would be perfect for both, small volume events with fast heatup, and large volume events with a bit of mass and a large fire.

I wanted to go as this as 1.5", coverd with a mortar cap that is reinforced with a steel fibre.

Make sure your mortar cap material and fibers are good at high temperatures.

Offline vtsteve

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Re: Minimum dome thickness
« Reply #7 on: February 26, 2018, 10:11:37 AM »
Thank you very much!

Yes my main goal is to fasten up heat up times. First I thought about a steel dome, which would clearly have the fastest heat up time but since I have to do lagrge volumes that makes heat stability too bad. So a thin stone dome would be perfect for both, small volume events with fast heatup, and large volume events with a bit of mass and a large fire.

I wanted to go as this as 1.5", coverd with a mortar cap that is reinforced with a steel fibre.

If the bricks are too thin relative to their inward-facing area, then the only thing holding them up is the mortar bond to the cap, and whatever mechanical engagement they have with adjacent bricks. It doesn't take much movement for them to tip and fall, especially in a flat Neapolitan-style dome. It would be much more stable as a solid casting (the cap IS the dome).

On the old Forno Bravo builders forum, there was a member who made a steel dome (cut from the end of a propane tank). He cast blocks of home-brew refractory in place on the outside, over steel pins welded to the outside of the dome - the pins helped hold the refractory in place. IIRC, he used crusher-run basalt mixed with lime and Portland cement for the outer cladding.

Whatever you do, make sure there's lots of good-quality insulation *under* the dome and the floor.
« Last Edit: February 26, 2018, 10:15:39 AM by vtsteve »
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Offline LaLabbo

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Re: Minimum dome thickness
« Reply #8 on: February 27, 2018, 03:24:47 AM »
Thank you Steve! Some very useful information!

What do you mean with insulation *under* the dome?

I already realized that good insulation is a must!


Maybe i will go a bit thicker with my dome stones.


What's your opinion regarding steel reinforcement?`


Thanks!

Offline vtsteve

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Re: Minimum dome thickness
« Reply #9 on: February 27, 2018, 09:48:12 AM »
The entire hot zone (floor *and* dome) of the oven must rest on good insulation, or it will bleed heat into the base and you'll have a hard time maintaining temperatures. Two inches of calcium silicate board, or 4 inches of perlcrete/vermicrete is the bare *minimum* that I would even consider using.

Some European builders use Hebel block (autoclaved aerated cement), but it's not a cheap/common material where I live. I don't know the insulating efficiency or longevity under a hot oven; I'd still use some cal-sil directly under the oven.
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Offline LaLabbo

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Re: Minimum dome thickness
« Reply #10 on: March 15, 2018, 11:29:10 AM »
So my plan is now to build a hybrid: soildiers at first with "normal" stones, afterwards a stainless steel dome with additional stones on top as additional mass.

Stones already arrived

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