2024 Neapolitan oven build

[daidensacha]

Toiletman I’m not a professional, only a life of experience doing all sorts of things. I worked a bit with concrete, but not a lot.

With regards to the calculations, I didn’t go to your lengths. But I have a few friends here, one retired builder (he said its bomb proof), another studying to be a building project manager (with a father who is a builder). I spoke with them both separately, and was assured by them it would be strong enough. I was told that 8 mm rebar is standard here in such applications, and would have been plenty strong enough. Using 12 mm was what I had at hand, so I used it, and it really took effort to bend it up using a vice and a piece of water pipe.

Casting the hearth slab and landing at the same time was a no brainer, as the strength of one piece of concrete will increase as it cures. Together with the added tensile strength of the rebar, I don’t see it cracking or breaking.

The landing weight calculated at 2700 kg per m³ for dry concrete.
1. Forward of the front of the oven (1350 x 250 x 125mm) is 113 kg. (149 kg with granite fitted, not substantial in my view given the rebar added)
2. Part sitting over the hearth slab (1350 x 114 x 105mm) is 43 kg.

Granite Assoluto Nero at density 2700 kg m³
Size: 1480 x 300 x 30 mm - 36 kg

The decorative arch will sit on top of the back part of the landing, joined to the vent arch with cement. I hadn’t planned on this being a source of reinforcement, but it will add weight to the rear of the landing reducing any forward stresses. I’m counting on the tensile strength of the rebar preventing any cracking. When I come to build the dome it will be well cured, and I will give it a test. I’m around 80 kg, so at some point i’ll post an image of me standing on it. In normal use, it will only have some pizzas sitting on it, maybe a tray of meat, or an elbow and a beer or two. No plans for heavy loads at all.

This build is one I am enjoying, and a process I am breaking up into chucks as I am working simultaneously on 2 other projects that fit with it. The 45 m² terrace with a roof which will house the oven, and a balcony extension with staircase that leads us down to the rear terrace and back garden. RIght now I am working on the render of the stand, and then onto the paving of the terrace, followed then by the terrace and roof. Here in Bavaria with the inclement weather I’m holding off starting on the oven dome until it is covered by the terrace roof. Then I can enjoy the dome build without worrying about being caught by a downpour that my floor insulation will soak up. Once the terrace is up I expect the build to go much faster.

[Toiletman]

Thanks, that's really clear. You mention you also did some calculation on the strength of it? What kind of calculations did you do? Do you have a professional background in this area?
I watched some online lectures on concrete calculations and reproduced them for my cantilevered slab, as well as doing some exploratory FEM work on what the loads on the brickwork would be. I would assume that any of the typical designs here are way overdimensioned like they should be, and also your ledge won't get any significant loads right? (probably it's own weight is significant). I assume you calculated it to be able to jump on it right?

[daidensacha]

What a wonderful looking build, and great details also in the planning and design considerations you put in. Could you share any details on the rebar in that 'front shelf' you made? It looks quite amazing floating like that.

I cast the shelf at the same time I cast the hearth slab as I reasoned it would be stronger this way. It was actually quite easy to plan the formwork for the shelf as I the concrete cascades back into the slab from the shelf.

I have 5 x 12 mm (1/2“) rebar lengths that go from the back of the slab 40 mm from the top of the slab to the front of the shelf. The 2 outer on each side have 90 degree bends, to account for the difference in height of the shelf to the slab, and are positioned 40 mm from the bottom of the shelf, and have 90 degree bends at the front to connect with the corresponding rebar on the opposite side. I put some 8mm rebar mesh in the shelf, wired to the rebars.

The center rebar is slightly different in that it has 45 degree bends to account for the different height of the shelf, runs from the back of the slab to the front of the self. I figured the combination of the rebars with 90 degree bends and 45 degree bends would add to the strength.

Formwork for the shelf.


Side view sketchup diagram for the shelf and slab with the rebar positioned. Doing this in sketchup was a really good process. Basically wanted the 30 mm granite that will sit on the shelf to sit flush with the floor of the vent landing bricks.



I have 12 mm (1/2“) rebar at 300 mm spacing 40 mmm from the bottom of the slab running front to back, and side to side, wired together. Tied in with the 8 mm vertical that is concreted into the cinder blocks.

Lastly, on each side of the concrete arch under the front of the slab I have 2 vertical 12 mm rebars that also give support to any forward stress.

I left the formwork and props on for just over a week before removing them, and we had a wet week which worked out well for the curing process.

These additional images are to add some clarity to what is explained before. Hope its clear.
This image shows the side view of the rebar that extends from the front of the shelf to the back of the slab. The rebar with a 45 degree bend is positioned center. The second and third have 90 degree bends, and are positioned more to the side of the shelf. On top of these in the shelf, I wired rebar mesh, not that it was really needed by my calculation, but more that I didn‘t want to regret later not adding it.

[Toiletman]

Formwork removed

What a wonderful looking build, and great details also in the planning and design considerations you put in. Could you share any details on the rebar in that 'front shelf' you made? It looks quite amazing floating like that.

[daidensacha]

Formwork removed

I removed the props and boards supporting the oven hearth and also the formwork on the attached countertop.

The conduits I inserted in the hearth concrete for drainage were easy to locate and I‘m holding off drilling out the tops until I‘m ready to start on the dome.

Want to lay a row of bricks on the back of the countertop, and render the whole stand in the coming week before I head of to France for a weeks holiday.

[daidensacha]

david s That link is a good read, thanks David.

The shelf will sit flush with the front of the vent arch, which will be 334 mm plus the width of the decorative arch bricks from where the vent meets the oven opening. There will be a 12 mm heat break in the vent, so the granites exposure will be limited to radiant heat from the oven.

im yet to stand in front of this type of oven at heated temperature, but I’m sure you have plenty of experience with it. In winter here it can be cold, usually min temp somewhere between 0 to -7C. I don’t think ithe granite will reach super hot temperatures, but I guess I’m gonna find out.

[david s]

Granite is well known not to like heat because it is sensitive to thermal shock and therefore not a great choice for a wood fired oven, Not sure how close you plan on it being to the heat source, but the combination of heat from the oven on a cold night could be problematic.

"Thermal shock can be exacerbated if the temperature fluctuation is uneven throughout the material. As a material cools or heats too rapidly, tensile stress between the surface and inner layers develops. Depending on the chemical makeup and bonds of a given material, the tension between layers will force the chemical bonds to break."

Fingers crossed.

https://www.colonialmarble.net/hot-p...%20for%20yours.

[daidensacha]

That is some pretty fancy shelf and hearth concrete work.

I have a nice piece of black granite, “Nero Assoluto”, 1450 x 300 x 30 mm that will sit on the front of the shelf, the second tier is for the decorative arch. Handmade green moss 125 x 125 mm Italian tiles to go around the front of the shelf under the granite. That second tier sits level with the top of the insulation fibre board, and the floor bricks will meet the granite at the front of the arch. Did all the plans in Sketchup, down to the millimeter and knock on wood, it came together perfectly. I’m really happy with the result so far.

[UtahBeehiver]

That is some pretty fancy shelf and hearth concrete work.

[daidensacha]

Hearth slab and countertop slab competed.

One week since I poured the hearth slab, so today I removed the formwork. I kept it covered with a tarp this week, and watered it intermittently. Two 20 mm PVC conduit inserted at the front of the hearth slab for electric cable that will power lights mounted on the front of the oven arch surround.

I also inserted 6 conduits in the concrete that sit on the wood base support, and stop about 15 mm from the top of the slab. When I remove the supporting boards under the slab, I’ll drill out the top 15 mm of concrete covering the conduits. Hopefully it is enough to allow drainage of any water build up under the mosaic tiles sheets between the slab and the insulation board.

I poured the shelf on the front of the hearth slab at the same time I poured the hearth slab. It has 5 lengths of 13mm rebar that run from the back of the hearth through to the front of the shelf, 4 with 90 degree bends, and one with 45 degree bend allowing for the difference in the height of the shelf and the hearth.

Two days ago I poured the joining bench (75 mm) top slab, on which I plan to lay a 30 mm granite plate. I’ll remove the formwork for this in a weeks time.

Next steps, clear up around the base and prepare for rendering the base cinder blocks. Then I’ll do the terrace paving before building the terrace roof which will allow me to work rain free on the oven dome.

[NCMan]

Having done this type of work for a long time, I'd wait much longer before pulling the forms, but nothing terrible will happen if you remove them that early. Bottom line, the longer you can retain moisture in any concrete or masonry, the better it cures. When I build ovens, I cover up the concrete w/plastic and cardboard (to block the sun)and leave it alone for as long as I can, including leaving the forms on.

[daidensacha]

Hearth Slab

We had a lot of rain in the last weeks in Bavaria, so not the best conditions to prepare the formwork for the hearth slab. Made the most of one rainy day to work on the formwork for the front shelf in my workshop. Also worked in sketchup on the rebar bends required for reinforcing and the shelf. 5 lengths of 12 mm rebar extend from the shelf into the rear of the hearth. Joined with rebar across the width of the shelf, and with rebar mesh.

Finally this week with some rain free weather I was able to knock up the formwork for the hearth slab, and yesterday I poured the concrete.

I could use some input with regards to timing for removing the formwork from someone who has experience in this. From a resource I found via Google, I would follow the following recommendation. Open to input or corrections.

Remove hearth side forms after 2 days.
Remove shelf formwork and props after 1 week.
Remove hearth supporting forms with props after 1 week.

The concrete should be cured after 28 days. I’m guessing it would be ok to start work on the oven dome before the 28 days, although I do have other work to do to bide my time.

[daidensacha]

Oven base block work finished view

After laying the last course yesterday I filled the blocks with concrete, apart from the two top front opening blocks. Today I’m making a form for a concrete arch I will pour at the top of the front opening. Rebar will be inserted in the sides before filling those last blocks with the arch formwork. Then I can get onto building up the formwork for the oven hearth.

[daidensacha]

Oven Base and Adjoining Bench

My vision for the oven is to have a half round back on the base. The fall of the oven dome will meet the sides at the back of the base, so any water or snow that does blow under roof will have no place to sit, and should run off and down to the floor.

My cinder blocks are 500x250x175 mm (LxHxW), with end blocks the same dimensions and also a half length end block 250c250x175mm (LxHxW).

I played a lot in Sketchup with different ways to cut the blocks and to join them so I can get the curve. They needed to be short enough so that once rendered I can cover the difference in the straight edges.



I created a template that fitted on each block so I could mark the cuts.



The blocks were not expensive, but also not the best quality, varying in height around 5mm. I could have used spacers, and did in places, but opted for setting each block with mortar to maintain a level surface for laying the next course. In retrospect, I would not choose these blocks again, and would fork out the extra 40 Euro to get the quality blocks, which I assume would be more uniform in height and easier to lay.

Took me two days to build the base as cutting the end blocks took time, and I opted for cutting joints in instead of a miter.

[daidensacha]

Oven Foundation planning and preparation

Before starting on the oven, I had to excavate, fill, and compact 9000x5000 mm area 400 mm deep for the new terrace. Took 20 tonne of broken limestone to fill the terrace area, and we had 40 cubic meter mountain of earth in the middle of the garden that we needed to dispose of. I finally finished that part 2 weeks ago, and started work on laying the oven base foundation last week.

Here is the layout plan of the terrace with the desired oven base together with a bench beside it.



The finished slab is layer directly on the compacted broken limestone (“Frankenschotter”). The slab is 200mm thick, and the top will be apron 100mm higher than the level of the terrace paving so no water can run under the oven (wood storage), or under the bench. I’m building a roof over the terrace, so have 50 mm fall over 5 meters.



I also ran electricity cable under the terrace to the oven as I want to have lights on the front of the oven for ambiance.