2024 Neapolitan oven build

[daidensacha]

I was looking through some old drawings and came across these ones that you might find helpful. Regarding the steel bracing of a low dome you may be interested in this method which does not require pinning the band to the supporting slab either side of the entry. Obviously you can't have the band across the front of the entry.

There is so much I don’t know, but I’m never shy about asking questions when I don’t. I spent the whole day yesterday reading and researching. In searching the forum for more info about heat breaks, I came across Napolitian style 106cm build inside a hobbit house with images showing exactly as you illustrate. His brickwork is really a sight to see.

I have options, that doesn’t look hard to do, the angle has threaded rod connecting the two oven the arch. He has two uprights to give support to any pull from the dome. Stainless band is available here and not expensive. What’s not clear yet is how he created tension in the strap. I was looking at metal pallet band last night, and how they fasten that. Yesterday I also looked at yachting stuff, for tensioning ropes to see if I could adapt that to this application. What he uses in his images I have seen before, but I’m not sure what it’s called, and I’m still googling to find out.

I attached this image to show how i did a quick mock up with the angle at the side so the arch. On the left I did another mockup with a smaller opening for the flu, and a 10mm heat break between what would be the decorative arch in red and the outer arch. I have scraps of “Siebdruckplatte”, high quality ply with waterproof coating on it, which is great for making non stick formwork. Perfect for the oven vent.

[david s]

I was looking through some old drawings and came across these ones that you might find helpful. Regarding the steel bracing of a low dome you may be interested in this method which does not require pinning the band to the supporting slab either side of the entry. Obviously you can't have the band across the front of the entry.

[david s]

Any gap to reduce heat transfer by conduction does little to prevent heat transfer by radiation, but a gap of around 8mm does work to reduce heat transfer significantly.
I cast my flue gallery using castable refractory. But as the flue gallery sees much lower temperatures than the oven dome or floor there are alternatives. I don't think standard concrete is adequate, but using the homebrew as a castable does stand up to the service temperatures we use ok. Creating a mould, then making a casting from it that will release properly is difficult and not really viable for a one off cast. However a hybrid solution is far easier to make using a sand hump mould covered in cling wrap, reduces thermal mass and also allows for a much shallower entry which makes working the oven far easier. The drawing should tell the story. It show a butchered anchor plate set into the wet casting for later attachment of the flue pipe. The second drawing shows how a more funnelled gallery performs better.

[daidensacha]

david s In the image above, if I would reduce the depth of the outer arch to 1 brick - 230mm, and and the vent to half brick - 114mm, the vent would then be 373mm wide and 114 mm deep. I hadn’t accounted on the measurement to add a decorative arch, so this would then allow me 114 mm at the front of the outer arch to have a heat sink (What size gap is recommended?) and then a decorative arch which would protrude from the final mortar coat.

This leads to my next question, with what do you cast the vent? I asked the supplier I am buying my materials from if I need refractory concrete, and he replied while he’s not an engineer, he thinks normal concrete would suffice.

In my plan I have an inner flu made from same material as firebrick, with a 25mm gap filled with fire blanket, then bricks and mortar. Between the arch and the flu I’m building formwork to cast my own. This will be covered with mortar, with bricks in the front. It will take the weight of the chimney, and flu. Is concrete a good material, or would vermicrete at say 5:1 be good?

[david s]

Creating a flue gallery in brick seems to be popular, but has some big drawbacks. Firstly it is really heavy and it therefore tends to act as a heating, drawing stored heat in the dome then lost up the flue and from any of its surfaces that are not insulated. This is the reason some builders isolate it from the dome in order to reduce heat transfer by conduction.
Secondly constructing curves in small brick units is difficult and introduces many weak points.
using sheet metal, preferably stainless is a good alternative because it can be made relatively easily and results in much lower thermal mass. Overcoming the massive heat sink problem.
I place a gap between the outer decorative arch and the flue gallery because my cast gallery is quite light (only around 10kg or so which means not too much thermal mass to act as a heat sink. By doing this it allows the inner oven and gallery to heat and expand as one unit, but still having room to move inside the cooler outer shell which has the outer decorative arch integrated to it. I’ve seen many ovens with cracked front arches caused by the inner oven parts expanding against the outer and cooler decorative arch..I use blanket in the gap, sealed
off with some 6:1
Vermicrete.

[daidensacha]

Insulation and Heat Break.

I’ve been struggling to understand exactly what it is and how/ where to incorporate it. I’ve read many explanations, but i can’t grasp the gap. In Insulation and heat break I found a little clarity.

Some put the heat break between the oven arch and the front arch, which David says means it will be warmer. David places his between the front decorative arch and the flu vent I think if I understand correctly, which is cooler.

I this plan, I made my vent 230mm, 1 brick in depth, whereas formerly I had it at 114mm, or half a brick, and wasn’t sure it was enough. As it is now, I could incorporate a gap between the inner arch and the outer arch, filling that gap with insulation to prevent heat loss. Is this correct?

Also, is the size I have planned for my vent overkill, and could I get away with half a brick depth? I want to eliminate as much as possible smoke venting from the front of outer arch.

What to fill the break with? 8:1 vermiculite mix with clay or lime instead of cement?

[daidensacha]

I could use some input on what concrete mix to use for the oven base foundation. I’ve read so much online that it’s getting confusing. It’s not fixed or 100% decided yet. I’m considering (need my wife’s stamp of approval first) laying a 9x4 metre concrete slab for a terrace at the rear of our house. It’s the best place for the oven, protected from wild weather, and it will become an outdoor kitchen entertaining area in warmer weather.
I have access to a concrete mixer, and trailer to get sand, gravel, and cement. A slab this size would be 5.4 cubic metres at 150mm thick. I saw a post by “david s” where he advises 1:2:3 mix of cement, sand, gravel, but I think that might have been for a hearth.
Any input or advice on the concrete mix, also the gravel size would be appreciated. I also contacted a local concrete delivery service to see what they charge for the equivalent quality. This quantity with a mixer is a lot, and It may kill me.

Some years back I build raised garden beds at the back of our block. 5 separate beds, each with 4.8 linear metres x 1 metre wide beds. The lower 500mm is .88 cubic metre concrete walls 500mm high x 150mm wide. I mixed the concrete in a mixer, each took 2 hours mixing, pouring. I was a task. In total 4.88 cubic metres, so if I do this slab, then I thing ordering it in is by far the better option.

Could still use input on the concrete mix for filling the cinder blocks, and the hearth though.

[david s]

david s Food for thought, I have some contemplation to do.
Two courses of staggered (on bond), if I understand correctly, your saying an option is to cut the soldiers in half and lay them as the other bricks in the dome. A quick calculation in Sketch-up (image attached), I could do 4 courses which would take me to within 4mm of where my dome curve starts as it is now. I wouldn’t have to change the curve, could have the dome I want, only without soldiers and it would be stronger.

Casting is not an option for me, not now anyway. It would be really easy to put two stainless eyelets in rear of the front shelf I will have joining the hearth, right beside the arch pillars. Stainless strap would also be easy.

You seem to know a lot about the Vermicrete too. I mentioned this, but with 75mm-100mm fire blanket, covered with chicken wire, and then 150mm of vermicrete, just wondering how strong and how much support this would also give to the soldiers? It’s not exactly an external buttress, but it must also give some level of support to reduce outward stress on the dome?

Yes, two or maybe three courses of half bricks laid on bond is far stronger.

Regarding vermicrete you can make it stronger. but doing that reduces insulation value (see table).
I use around 2" of 10:1 vermicrete over the blanket to even out lumps and bumps, restore a nice shape and to provide a firm substrate on which yo apply the outer render. The 10:1 mix has about the same insulation value as blanket (again see table) I see no benefit adding chicken wire over the blanket (although most builders do) because it takes so long to apply over a compound curve, compresses the blanket reducing its insulation value, would do nothing to strengthen an already weak 10:1 vermicrete and adds a conductive material into a layer you want to be insulative. Others will no doubt disagree, there are many different ways to achieve what you want and the time/cost factors will vary from builder to builder.

75-100mm of blanket with another layer of weak 10:1 vermicrete over it will do nothing to buttress the base of the dome.

[daidensacha]

I spent the last few hours researching, and playing with my plans to see what option I like best. Actually adding stainless steel strap around the first course of soldiers is not a big thing. I’m grateful that David brought this to my attention so I could think it out now. I’ll add a few fixing points right beside the arch pillars in the back of the front shelf that will be poured with the hearth. It’ll serve a couple of purposes, mainly to reinforce the soldier course taking the stress of the weight of the Neapolitan dome. Secondly additional support for the shelf, which will be well reinforced with rebar anyway.

[daidensacha]

david s Food for thought, I have some contemplation to do.
Two courses of staggered (on bond), if I understand correctly, your saying an option is to cut the soldiers in half and lay them as the other bricks in the dome. A quick calculation in Sketch-up (image attached), I could do 4 courses which would take me to within 4mm of where my dome curve starts as it is now. I wouldn’t have to change the curve, could have the dome I want, only without soldiers and it would be stronger.

Casting is not an option for me, not now anyway. It would be really easy to put two stainless eyelets in rear of the front shelf I will have joining the hearth, right beside the arch pillars. Stainless strap would also be easy.

You seem to know a lot about the Vermicrete too. I mentioned this, but with 75mm-100mm fire blanket, covered with chicken wire, and then 150mm of vermicrete, just wondering how strong and how much support this would also give to the soldiers? It’s not exactly an external buttress, but it must also give some level of support to reduce outward stress on the dome?

[david s]

Mortar won’t stick to cal sil board, at least not to the stuff I’ve used, so there’d be little point in trying. Two courses of staggered (on bond) bricks is way stronger than laying soldiers.
A steel strap needs to be secured either side of the arch entry into the hearth as you have mentioned. Unfortunately steel corrosion is accelerated by both moisture and heat. You could consider stainless. Another alternative is to use buttressing, but this adds thermal mass in a location where you don’t really want it and it will require additional insulation around it. A further alternative, if you have your heart set on a low dome, is to cast it. If you have your heart set on a brick oven a hemisphere would be a far better choice.

[daidensacha]

You might be better off cutting a template of your required arc rather than using an IT.
Diagram explains why.

I had thought of that, and did make one about a month ago, along with a template for the floor to mark cut lines on the floor bricks. I also made ply templates for the individual brick sizes to mark out on the arch template. It’s in tow halves, stuck together with gorilla tape, so I can fold it and use in in the oven to check the height of the bricks as I lay the courses. See images below.

Oh yeah, also made the innner/outer arch forms too, if there is one thing when I start, I want to be prepared as possible. This has been long in the making, so really enjoying the process now. The tips and feedback from your forum make it ever so more enjoyable.

Just to add, I was planning on using both the template to check, and the IT to uniformly lay the bricks in a proper circle. I have done a bit of brick laying in the garden far from a professional so the IT will be my helper. I have all the measurements outlined in my spreadsheet, so have a reference to check. I have a good app to check angles, and my CAD drawings to take measurements from.

[daidensacha]

The popularity of the hemisphere as a form for brick ovens over the centuries as an all round best performer also relates to its structural integrity as well as its ease of construction. Extreme departure from the hemisphere usually requires either steel bracing or buttressing. Most manufactured cast oven today have much lower domes and higher side walls, because, unlike brick builds with their many mortar courses, they don't suffer from the same structural weakness.
As you've not departed radically from a hemisphere (only 16% lower) I'd expect you won't have problems, so may possibly not need bracing or buttressing.

Cool, just when I thought I had somehow scaled the hard part of my learning curve. I’ll confess my ignorance, and say that I went to google and found a great explanation of buttressing, along different types and with the historical applications.

In planning my oven I chose Neapolitan style, however I made the internal height 25mm higher than the recommended height for this style, also the inner arch height slightly higher. It’s still 75mm lower than a similar sized Tuscan style oven, so I kind of refer to it as my semi hybrid oven.

I plan to lay the first course of soldier bricks directly on the ceramic fibre board, with the floor bricks cut to lay inside the soldiers. I read that it is best not to cement the first course to the base, so they wont be stuck to the ceramic fibre. Hopefully the refractory cement holds them together, the thought had arisen as to what effect the outward force from the weight of the dome would have on the soldiers.

To this end I have been working on adding an additional course and changing the cuts of the courses 2-4. (Image attached) This has reduced the outer gap to 10mm, so hopefully there will be less chance for the outward pressure put on the mortar to fail. In the previous plan where the curve is really aggressive, the greatest gap was 17mm, which made me nervous. I’d rather not live with that knowledge once I’ve completed the oven, and the fear it might fail.

Question: The first course not being cemented to the base does worry me, although I’m not sure its possible to cement to the ceramic fibre board anyway. From reading, metal strap around the soldiers is the standard reinforcement used for Neapolitan ovens. Is it worth just adding that for peace of mind? This gives rise to another unknown, where the fixing points are at the arch? Only thing I can imagine is to have reinforcing rod points integrated into the hearth build. This would be quite easy, as I am planning on adding a shelf at the front of the oven, that will be connected to the hearth with rebar. (images attached) I could have a fixing point at either side of the back of the shelf, which will be higher than the hearth. Could metal strap, along with the arch at the front could be sufficient reinforcing?

[david s]

You might be better off cutting a template of your required arc rather than using an IT.
Diagram explains why.

[daidensacha]

UtahBeehiver Helpful, thanks. I will make a point of welding the bracket so the center of the square tubing lines up with the center of the bricks. When pivot the bracket to adjust for each course, I’ll also be checking the top angle and inner angle of the bricks when setting the bracket. I’ll have to watch that. I made a floor template out of 6mm ply and using this will make measurement markings on the square tube for the initial courses. I can also make measurement markings for each additional course as a check when I get to the higher courses.

I did have a question, I have been reading through JRPizza build as you suggested. When you remove a brick to set the IT pivot at floor height in the center, how was it when setting that brick when removing the IT?

I’m enjoying reading though JRPizza’s build. It’s making me aware of lots of stuff I will probably encounter and haven’t even thought about. It helps to be mindful and to check levels and to really pay attention to where the course bricks meet the dome arch. I have been playing in sketch-up with intersecting my drawings of the dome and the arch to see how they meet, and where the joins will be.