2024 Neapolitan oven build

[daidensacha]

The chart I created with all needed measurements.

[rsandler]

You may also want to have a look at this thread: https://community.fornobravo.com/for...-table?t=16780. You can get the same effect with a jig by just tilting the bricks sideways, rather than tilting forward. Either way works (the dome calculator on the forum has angles for both), but by the top of the dome you end up having to tilt forward quite far to make the require bevel. To each their own, but the side-tilting jig felt safer to me.

[daidensacha]

rsandler Thanks for your info, I’ll read through it and see if it suits me. I think if I was doing a Tuscan oven which has the same radius for each course, it would probably work for me. With my Neapolitan build, each course has a different radius, and the curve of the dome changes a lot. What I like with the jig I’m working on is that I can set the radius for each course, and on the whole jog pivots from that center point. To the left of the blade for the right cut, to the right of the blade for the left cut, no guess work, super accurate, ……. I hope. I devised a mechanism to lock the bricks in, so they will be secure, as long as I don’t force the cut it theoretically should work well.

Never say never though, will read and assimilate the info in the link. I had a preliminary read, need to nosh it out a bit first.

Update: It’s actually really cool. Definitely like the sideway tilt over the forward tilt. I could calculate my angles quite simply to use it. I’ll update the thread when I have a working jig, and with photos to show which i ended up using.

The dome calculator is new to me too. It is purely for the Tuscan style dome though, going by the calculated dome height when I enter my oven and brick sizes.

[daidensacha]

Indispensable tool.

I started this last year, time to finish it in preparation for spring and starting the Neapolitan build.

So I used a castor which was cheap and easy to adapt, with some mild steel rod. One rod inserts into the larger, with a nut spot welded to the tube so I can adjust the length of the arm. Crucial given the curve of the Neapolitan dome. I have to finish welding the bracket on the end, but made it so I can adjust the angel, also needed for this build as I want to set the angle for each course of the bricks so the dome goes to plan.

Its light, sturdy, soon to be finished.

[david s]

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.

[UtahBeehiver]

Critical design component. From the pivot point along the center of the square tubing MUST intersect the center of the brick or the brick will not be perpendicular to the center of the floor and will see stepping of the lip of the brick courses as you move up. There error induced in cumulative so the higher you go the more error.

Also, be aware, ideally the pivot point should be at floor level and at the center of the floor. By using a caster it dome height will change as you move up. Just something you need to be aware of and adjust the radius to suit your build.

[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.

[david s]

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

[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?

[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.

[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]

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?

[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.

[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 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.