2024 Neapolitan oven build

[daidensacha]

attached is an experiment I did for drying a vermicrete slab that helps explain what's going on.

Gone is my ignorance as an excuse. While I have it clear now the order of how to lay the vermiculite if I do decide to do it, I’m not sure I will. Last summer here was an anomaly, lots of sun, usually it is overcast with dark clouds, and really humid. It would take forever to dry the vermiculite layer. even with holes in the hearth and without the dome preventing evaporation. Once the dome is on and the vermiculite covered, I’m not sure how it actually would dry. 1) Vermiculite and Perlite hold the water, water wicks upward, and with the exit 150mm holes in the bottom of the hearth, it kind of goes against the natural flow for the water to get out that way.

Thanks for the info David, looks like I’ll be sticking with the original plan and using just the 100mm Ceramic fibre board. I’ll stick wth the 100mm because the price difference between 75mm and 100mm is minimal.

Delve a little deeper into your block suppliers catalogue. You should find half height blocks, they are commonly used in block work.

I’ll visit my local “Baywa” who supply builders and tradies as I have an account with them and they 1) love Australia, and 2) are super friendly and helpful. Last resort is I can knock up a cutting jig to guide my 125mm angle grinder with diamond blade, a few hours of dirty work wearing a mask.

[david s]

One of several builds I have watched on Youtube that I found really helpful is Wood-Fired Pizza Oven step-by-step in Romania. In it he encloses a vermicrete insulation layer in the hearth, and at 5.22 it shows he puts glass mosaic tiles on the vermicrete before adding the ceramic fibre board. The bottom of his hearth under the vermicrete is very thin although reinforced and with supporting wall under it in the centre of the base. This would be contrary to my question in the previous post re: placing the mosaic layer under the vermicrete.

I would build a thicker base, as I want to include rebar that comes out of the hearth and supports a landing in front of the oven.

Yes this build has that all wrong. Because a basin has been created it is asking for water to accumulate there and there are no drain holes. The tiles should have been placed in the bottom of the basin with the insulation on top..

[david s]

david s I understand you said in your opinion its not necessary to have additional vermiculite insulation on the hearth under 100mm ceramic fibre insulation floor.

In my case, here in Germany we have schalungssteine, which are quite a different format to cinder blocks. I‘m using L500xH250xW175mm (Illustration below.) Aiming for my final height of 1150mm for the floor, it requires cutting the fourth course of blocks down to 136mm. I‘m considering the possibility of eliminating the fourth course altogether, which leave me with 86mm to fill, which I could with a layer of vermiculite/perlite insulation. In the plan below, the hearth is 150mm (100mm above the wall, 50mm inside the wall), so I would need to change that to 150mm above the 750mm wall. It would reduce the height of the space below the hearth from 886mm to 750mm, but would save me on blocks for the fourth course, and the cutting of the blocks.

Above the hearth, it would then be 86mm Vermiculite/perlite insulation, 100mm Ceramic fibre insulation, 64mm firebrick floor, total of 250mm. My floor will be inside the dome first course with the come first course on the ceramic fibre board. (Image below right)

Question: Would also do away with the need to put mosaic tiles? I‘m a bit unclear about the order and structure with this. I see the advantage of putting drainage holes in the hearth, which is straight forward and planned. If I do the vermiculite/perlite layer, is there a way to lay the mosaics under it, perhaps covered with a layer of plastic with holes and then the vermicrete? Or not necessary then at all?

Question: Vermicrete/Perlite mix. For this layer of insulation under the ceramic fibre, what ratio would you recommend so that it is strong enough to support the ceramic fibre and then oven? I considered laying an extra layer of concrete around the vermicrete on top of the hearth to enclose it on the sides. I could do this, or leave it, depending on whether it would be better for support of the vermicrete layer.

Delve a little deeper into your block suppliers catalogue. You should find half height blocks, they are commonly used in block work.

Regarding the layer of vermicrete under a 100mm calcium silicate board I don't believe you'll achieve much because 100mm is already way more than most oven builders would use. The thicker the insulation is the more it suffers from the law of diminishing returns. Additionally the large amount of free water a vermicrete layer contains needs to be removed prior to building over it because moist insulation of any kind does not work very well. We've had reports of oven performance getting better months after completion because that underfloor moisture is difficult to remove. A 100mm cal sit is already dry so this problem is largely removed. However should water get in a space under the insulation created by a layer of tiles with wide spaces and some holes in the supporting slab, do a fine job of allowing moisture to escape. If you have your heart set on doing a vermicrete slab it should be a 5:1 ratio for sufficient strength. The vermicrete over the dome does not support a lot of weight so a !0:1 there is better. (see attached table for strength to insulation relationship). Some weed matting placed over the tiles is enough to prevent the vermicrete from blocking the pathway between the tiles, but enough to let the moisture pass. Also attached is an experiment I did for drying a vermicrete slab that helps explain what's going on.

Vermicrete insulating slab copy.doc.zip

[daidensacha]

One of several builds I have watched on Youtube that I found really helpful is Wood-Fired Pizza Oven step-by-step in Romania. In it he encloses a vermicrete insulation layer in the hearth, and at 5.22 it shows he puts glass mosaic tiles on the vermicrete before adding the ceramic fibre board. The bottom of his hearth under the vermicrete is very thin although reinforced and with supporting wall under it in the centre of the base. This would be contrary to my question in the previous post re: placing the mosaic layer under the vermicrete.

I would build a thicker base, as I want to include rebar that comes out of the hearth and supports a landing in front of the oven.

[daidensacha]

david s I understand you said in your opinion its not necessary to have additional vermiculite insulation on the hearth under 100mm ceramic fibre insulation floor.

In my case, here in Germany we have schalungssteine, which are quite a different format to cinder blocks. I‘m using L500xH250xW175mm (Illustration below.) Aiming for my final height of 1150mm for the floor, it requires cutting the fourth course of blocks down to 136mm. I‘m considering the possibility of eliminating the fourth course altogether, which leave me with 86mm to fill, which I could with a layer of vermiculite/perlite insulation. In the plan below, the hearth is 150mm (100mm above the wall, 50mm inside the wall), so I would need to change that to 150mm above the 750mm wall. It would reduce the height of the space below the hearth from 886mm to 750mm, but would save me on blocks for the fourth course, and the cutting of the blocks.

Above the hearth, it would then be 86mm Vermiculite/perlite insulation, 100mm Ceramic fibre insulation, 64mm firebrick floor, total of 250mm. My floor will be inside the dome first course with the come first course on the ceramic fibre board. (Image below right)

Question: Would also do away with the need to put mosaic tiles? I‘m a bit unclear about the order and structure with this. I see the advantage of putting drainage holes in the hearth, which is straight forward and planned. If I do the vermiculite/perlite layer, is there a way to lay the mosaics under it, perhaps covered with a layer of plastic with holes and then the vermicrete? Or not necessary then at all?

Question: Vermicrete/Perlite mix. For this layer of insulation under the ceramic fibre, what ratio would you recommend so that it is strong enough to support the ceramic fibre and then oven? I considered laying an extra layer of concrete around the vermicrete on top of the hearth to enclose it on the sides. I could do this, or leave it, depending on whether it would be better for support of the vermicrete layer.

[daidensacha]

That’s really helpful, I clicked with your reference to the difference in thermal mass and time taken to heat pre cast ovens vs brick ovens.

in my case with the thicker brick walls it would make more sense to go with 64mm floor as it will take longer to heat anyway. They should still be well heated by the time the walls are, and will retain the heat longer.

understanding this is a big thing, many thanks.

[david s]

Most cast manufactured ovens have walls of 2", some larger ones 3". With a brick build you are stuck with 4" thick walls. Anything thinner compromises the structural integrity because of the mortar joins. Note that in all brick wall constructions the bricks are never laid on edge to make the wall only 3" thick. So a brick build with 4"thick walls will always have more thermal mass than a cast oven with thinner walls, but will also take longer to heat and consume more fuel.

[daidensacha]

Thanks David,

I had read something along the lines you wrote that the thicker the floor the more wood and time required to heat it. My walls will be 114mm thick, with ample insulation on top. I was looking at the Premio100 with 50mm floor, and seeing how Clive from Wood Fired Oven Chef uses his. His oven takes 48 hours to cool down and he uses it to bake all sorts.
We will have pizza nights, and we have lots of family and friends, so on those nights it will get well used. I was originally planning on 64mm floor, then changed my plan to 50mm, to save on wood and cut the heating time. Question is if it will be enough to retain the heat. I’m thinking with the insulation I plan it should.

Many thanks for your feedback.

[david s]

Some people say you can't have too much insulation, but as the insulation is expensive and also is subject to the rule of diminishing returns, extra insulation will cost you more for a very small benefit.

Q1. 3" of insulating board is quite sufficient IMO
Q2. The floor thickness should match the dome dome thickness. Some builders, typically those who want to bake lots of bread like a really thick floor an turn their floor bricks on edge to get a 4" thick floor. But remember the thicker the floor and dome are, the longer it takes to saturate it with heat. If you have really thick walls and floor, you won't be keen to fire up the oven on a Friday night to cook 3 pizzas. And you better have access to a lot of free wood.

[daidensacha]

Hi All,

Long been on my bucket list to build and planning to start this year in spring.

I want to cook primarily Neapolitan style pizza. I also want to make use of the retained heat to cook meat, and bake bread in days following a pizza bake.
To this end, I’m weighing up the balance between size of fire, of wood and time required to heat the oven, and the best insulation and floor thickness to cook with and retain heat.

Neapolitan Style Oven Planned specs.

• Base insulation: 75mm ceramic fibre board. (Unsure if its worth adding 100mm vermicrete under the ceramic fibre board)
• Oven floor: 50mm thick firebrick plates. (leaning to 500 x 500 x 50mm, although 500 x 500 x 64mm also available)
• Dome:
  • ID: 1020mm
  • OD: 1248mm
  • Inner height: 426mm
  • Outer height: 540mm
• Dome Insulation: 75mm ceramic fibre blanket, covered with 100-150mm vermicrete (ratio 1:8)
• Opening:
  • Width 500mm
  • Height 280mm

Question1: Floor insulation

Is 75mm (3”) ceramic fibre board sufficient to retain floor heat, or would it be worth adding additional 100mm vermicrete insulation under the ceramic fibre? That would by my reckoning give it the equivalent of 125mm ceramic fibre insulation. Overkill?

Question 2: Oven floor brick thickness

I want to make use of the retained heat in the days following a pizza bake. General consensus is that 2.5”/ 64mm is best, but I noted that the Forno Bravo Premio100 Home Pizza Oven Kit uses 75mm ceramic fibre with 50mm floor on top. Clive, the Wood Fired Oven Chef who has a brilliant Youtube channel built his oven using the Premio100 and he says the retained heat is really good. Is it worth going for 64mm thick floor, or is the 50mm sufficient?

Appreciate any feedback or info.

Looking forward to posting as the build commences.