Isolation stones useable??

[atak]

Goodmorning, after selling our house I want to built a Pizza oven again in our new house.
It will be a napolitan oven again.
My question: I have 100 isolation bricks laying here, can I use them as under floor for the pizza oven built? or are they to soft to built a oven upon them.
Thanks, Adrian.

[UtahBeehiver]

Insulating fire bricks (ISB) will work as insulation under the standard fire brick floor. Typical ISB have a thermal conductivity value of 0.15 W/(km) vs 0.05 for CaSi board. Not quite as good as CaSi but if you have them use them, they are typically very expensive, use what you have, turn on edge if you want more thickness and insulation since you have a 100 you have plenty.

[atak]

Thank you very much for the answer, so I can build the whole dome on it? , Adrian

[UtahBeehiver]

No on dome only under floor bricks, they are too soft and cannot handle the abrasion and will not store heat,

[rsandler]

To elaborate on Utah's comment, the sequence of the structure, from bottom up, needs to be:
1. Concrete stand
2. Insulating Bricks
3. Dense firebrick floor
4. Dense firebrick dome
5. Insulating layer (CF blanket, perlcrete, vermicrete etc.)

That is, assuming what you have is insulating firebrick, they aren't going to crumble under the weight of the dome, but they aren't suitable to be an exposed surface for multiple reasons. If you want to double check that what you have is stiff enough, just try standing on one of the bricks. Despite the large overall weight of a brick oven, the pressure on the floor/insulation comes to around 2-3 pounds per square inch (PSI)--rather less than from a typical adult human standing on one foot.

[atak]

Thanks for the answer, I am starting with the foundation tomorrow and will use sand-lime bricks for the walls and big slates concrete from 2000x1000x0.10 as floor for the ofen, I have that all laying around my home,

[UtahBeehiver]

Can you confirm the thickness of the big slate concrete being used for the top of the brick walls, 0.10??, assuming 2000 and 1000 are in mm. These ovens get really heavy and should have a min. of 4" of rebar reinforced concrete or equivalent material.

[david s]

I'm assuming slate=slab

The preparation for foundations depends on climate, soil type and depth, slope, if any and weight it has to support. If in doubt consult a local building professional, but
the usual build procedure followed by most here is a 100mm (4") concrete steel reinforced foundation slab on grade, over compacted aggregate, followed by 4 courses of concrete masonry unit CMU blocks with their cores filled, (go another half height block course if you want it higher if you're tall). Topped off with a 100 mm (4") concrete steel reinforced hearth supporting slab.

This alone is considerably weighty. Because my ovens are small there is less weight to support than a larger oven so I've reduced the CMU blocks to two piers only and reduced the selection of their width to 140 mm (6") This has the additional advantage of being open at both ends providing airflow into the wood storage area. A cantilevered slab, whilst requiring more complex formwork, also provides a more weatherproof cover for the wood storage area underneath. Dry wood is essential. The reduced span of the stand also allows for a thinner hearth slab reducing weight, materials, labour and cost even further. (See second drawing) But be aware that the strength of any concrete slab is proportional to the square of its thickness. ie a 2" concrete slab whilst being half the thickness and weight of a 4" one, is only 1/4 of its strength.

[atak]

Hello, no I really mean a concrete plate, these one's https://www.nedabo.nl/p/betonplaat-200x120x10-cm/
I make 4 walls where I lay on the concrete plate.
Can the walls made from sand-lime bricks, they are 43x20x10 cm and will be 2 besides each other or is that to weak.
In Holland we build houses from it, two stories high.
Sheers, Ad

[UtahBeehiver]

I think I know what you mean but how about drawing a little hand sketch similar to what David did so we can be sure of your base, wall, hearth concept.

[david s]

The build begins with foundations of a sufficient area and strength to support the oven which it supports, but teh process begins with the oven design, specifically its size and type. There are a number of variations including brick, refractory, hemisphere, half barrel, low dome etc. Much will be dependant on how and what you want to cook.
Once this has been decided the size (internal diameter) can be used to figure out the required area for the stand, hearth and foundations. A plan for both front and side views should be made to include requirements for the vent and chimney. If my sketch approximates your plan you can use it to show the appropriate thicknesses to make your calculations. The weight can also be calculated once the area and therefore the volumes and densities of the materials used. For calculating dome volume use 4/3 x pi x r3. We can help to estimate this if you can provide the info for your proposed design.

[Toiletman]

Hello, no I really mean a concrete plate, these one's https://www.nedabo.nl/p/betonplaat-200x120x10-cm/
I make 4 walls where I lay on the concrete plate.
Can the walls made from sand-lime bricks, they are 43x20x10 cm and will be 2 besides each other or is that to weak.
In Holland we build houses from it, two stories high.
Sheers, Ad

Hi Ad, have a look at the build thread of my oven please. I'm in Eindhoven now, but I grew up in Bennekom, relatively close to you.

With respect to the bricks to build the oven 'table': using kalkzandsteen will probably be fine, especially going 'volsteens' (ie. two rows). I used 'halfsteens' bakstenen (clay bricks, one row), which if I'd do it again I'd do in 'volsteens'. When I ask chatGPT to compare the compressive strengths of both the kalkzandsteen (lime sandstone) is typically double that of a ceramic brick. So no problem there. However, they do absorb moisture, so I don't know if you are going to put your table foundation under ground, and if your oven will have a roof, but you should prevent these walls from soaking up moisture, as they could then start chipping and cracking when they freeze over.
Besides that: you need special types of cement/glue for these stones, not just normal mortar.

With respect to the other materials:
- I've not seen anyone build with prefab concrete slabs. They'll be perfectly suitable for your table foundation IMHO (assuming your oven table walls will fully be on top of one slab, not across two). Using such a slab for the table itself could be ok, but it really depends on a lot of conditions:

1. How will the slab be supported?
2. How much and what size of reinforcing do the slabs contain? From your link they are typically used for paving paths, that's a completely different application than bridging across gaps. The 'double' reinforcement mentioned on the product page really doesn't mean much. What size of rebar is used, at what spacing?

From the manufacturers website this information does not become apparent so I'd be pretty hesitant to have such a slab 'floating in the air' with a big load such as an oven on top of it without knowing anything about its reinforcement or strength. Do you have experience using these slabs in such a way? Can the manufacture assist in calculating/guaranteeing that it will carry the load?

Like the others already said: it would be helpful if you share some sketches/plans of what exactly you tend to build. The materials of the oven itself are also important to get right. You mentioned that you moved houses and wanted an oven again. Did you build your old oven yourself? Do you have pictures?

[atak]

I build one once, https://community.fornobravo.com/for...low-dome-build

I will make a concrete slab on sand, we live in a sand area, of 13 cm thick from 200x300 cm. On that I place 4 walls of double lime/sandstone bricks with the hight of 1 meter [ 5 rows ] and 20cm thick

on that the 3 plates are lying,they are 100cm wide so they are hanging only 80 cm free and they are douple rebared , and on that I will build a 42" pizza ofen with a low dome like last time.

My scetches are to bad, I will make some better ones.

When I start building I will start a new post at the building forum

[david s]

I build one once, https://community.fornobravo.com/for...low-dome-build

I will make a concrete slab on sand, we live in a sand area, of 13 cm thick from 200x300 cm. On that I place 4 walls of double lime/sandstone bricks with the hight of 1 meter [ 5 rows ] and 20cm thick

on that the 3 plates are lying,they are 100cm wide so they are hanging only 80 cm free and they are douple rebared , and on that I will build a 42" pizza ofen with a low dome like last time.

My scetches are to bad, I will make some better ones.

When I start building I will start a new post at the building forum

Thermal conductivity is the reciprocal of insulation. ie the lower the thermal conductivity the better the insulation. Check the thermal conductivity of sand and compare it to perlite, vermiculite and calcium silicate as well as other materials to compare their insulation capacity.

https://www.engineeringtoolbox.com/t...ity-d_429.html

Sand is not a particularly good insulator. Calcium silicate board is about the best solution although a much cheaper version can be made using a 5:1 vermiculite or perlite and cement mix. This requires more labour and needs to have the bulk of the water eliminated from it before the oven is used.

[atak]

This is the place that it will be build.
I will drill some rebar in the foudation of the deck, just for security. minimum thickness is 13cm