Napolitian style 106cm build inside a hobbit house

[crisp]

Hi Daidensacha

The strap system was fabricated myself. It is kind of like a belt you'd have around your trousers. The strap goes through a shot in the buckle, bent back and riveted (rather than sewn) together (the same as a belt). The buckles have a long treaded bolt welded to them. Two (L shaped) angle iron steel posts were concreted vertically into the concrete base. I drilled holes in the concrete for the steel and once in place filled in around them with cement mortar. Once the straps were around the soldier course the bolt ends of the buckles were threaded through holes in the vertical angle iron posts. The straps were tightened with a spanner (nuts and washers). Since the straps could not go all the way around due to the entrance there is a bracing over the entrance (see earlier pictures). You could always use a chain instead of straps or perhaps build intermittent buttressing with firebrick around your soldiers. Think of a clock, the entrance being 12 and every 10 minutes a buttress. You might not need the 10 minutes past or the 10 minutes to because the entrance supports the outward thrust there. So you really only need 20 past, half past and 20 to. These buttresses only need to be one brick thick and because there are not built all the way around the soldiers they won't steel the the heat like a thicker solid wall would. Difficult to explain but I hope that might give you some different ideas to consider.

[daidensacha]

Hi All

I'm new to this forum, but have been reading posts on this forum for a while now. I've been so impressed with everyones different projects, ideas and Ive learned from you all. So I'd like to thank everyone for inspiring my build. There are lots of you out there that have built some fantastic ovens both indoors and outside and have experienced how the oven functions. I have a few questions which some of you have experienced. I am much obliged if any of you can answer some of my questions below.

Im building a Hobbit house in my garden, it's round building with a semicircular dome, basically the same as a huge pizza oven. The inside is a brick facade and the outside is in granite. Inside the domed walls of the Hobbit house i'm constructing a Napolatian style oven with 106 cm diameter.

I decided to build Napolation oven with a lower flatter dome. This required two radius's for the dome; a steeper first five courses on top of the soldier course; thereafter a flatter radius to the centre. There is more outward thrust for this type of dome shape, however, in my opinion a circular dome is also not stable without some form of buttressing, so I have incorporated a buttress harness. A catenary shaped dome or arch is actually most stable but wouldn't suit a pizza ovens design, read more here https://en.wikipedia.org/wiki/Catenary. Basically an inverted hanging chain which is the same length as the centre line of an arch/dome cross section, represents the line of thrust upside down. This invisible upturned line of thrust should lie in the middle third of the brick or voussoir, if it does not, then the arch/dome will be unstable without buttressing. This is why the gothic arch revolutionised spanning wider openings with less stone. Before this the Roman half circular aches and domes required higher/larger voussoirs to bridge wider openings, which meant that there was a certain limitation spanning wide openings.

I started the build on the 6th August and set the last keystone on the 16th August, so it's taken 10 long days of work to get this far. The first five courses where all cut to a steeper radius, however i only tapered the correct radius of the bed joint, not the perpendicular joints of these first five courses. After the first five courses, with the flatter arced dome, all the four sides of the brick voussoirs were cut to a different trapezoid for each course for tight fitting.
I have mixed my own mortar which is from clay / hydraulic lime / sand. There is no cement, both the hydraulic lime and clay is the binder with the sand. The hydraulic lime helps to harden the mix. Since cement was first patented in 1824 all ovens before this had no cement in the mortar. Hydraulic lime is a more flexible binder than cement and allows for for movement through thermal expansion. The joints inside the dome are 2-3 mm.

Now that the dome is completed, the next job is to build the vent and construct the chimney etc. There will be a heat break between the entrance to the dome which will be 10mm air gap sealed will fire rope. The hearth entrance to the inside of the dome entry arch is 60 cm. The pizza oven is built into the wall of a 9m² room.

Questions;

1. If the oven does not have a door, how will the radiating heat effect this small room when the oven is in full operation, will the room become unbearable to sit in without a door which can be closed? The door would have to be on the room side of the vent/chimney. I will have an insulated door for heat retention and longer cooking but this cannot be used to stop radiating heat into the room because it also blocks the vent. I'm wondering whether it's worth designing a door which can be closed within the rooms facade? If anyone advises to have a door then I need to incorporate this in my design, otherwise i might regret it later. Has anyone else built an interior oven who can tell me how hot it can get within the room?

2. Another question is insulating the dome. I thought that i would parge the dome first with clay / hydraulic lime / sand mix 2-3 cm thick to seal the dome (perhaps some chicken wire too). Thereafter, covering with 7cm of insulating concrete made with Leca / Hydraulic lime / clay. This will be a loose fairly dry mix with air voids. The rest of the enclosure will be Rockwool masonry insulation, this is slightly harder than normal rockwool. These materials are readily available to me.
Basically the clay parging firstly seals the dome; the Leca insulating concrete separates the Rockwool from the direct heat. Any thoughts on this?

I will post some more of the build at a later date

I came across your build yesterday researching about a heat break of all things, but what I found was more interesting. Your work is great. Especially relevant for me as I’m also builiding a Neapolitan style oven. In your phots of this post, you show your reinforcing with angle and metal straps. It’s just what I need to do, and have been exploring. Can you tell me what brackets you used at the angle to torsion the metal strap. Were they custom made? I have seem something like that, but I don’t know how they are called, and am not finding it in google.

[Alomran]

crisp ,

I saw a recent update of your build on a Facebook group page. Awesome! I'm sure many on this forum would love to see your final touches. How about posting some of those pics and videos here for those of us that don't do Facebook?

Would love to see his immaculate work. What's his FB address?

[Gulf]

crisp ,

I saw a recent update of your build on a Facebook group page. Awesome! I'm sure many on this forum would love to see your final touches. How about posting some of those pics and videos here for those of us that don't do Facebook?

[ubcpsyc]

I'm sorry. What do you do for a day job? This is way too beautiful.

[wotavidone]

I wish people wouldn't post threads like this.
Makes me feel inadequate and even less talented than I previously thought I was..

[manumit]

I check back on this thread every month or so to see if there are any new progress photos... *cough, cough* how's it coming along?

[UtahBeehiver]

Extremely well done brick work. Looking forward to seeing the final product.

[crisp]

[david s]

With such a huge oven your flue gallery is going to be a small percentage of the mass of the dome and floor so you may be better to place the thermal break/expansion joint between theflue gallery and outer decorative arch anyway. In that position it won't see such high temperature as well. I use a 6:1 vermicrete for the gap, but others use ceramic insulating blanket or just unfilled (air). The gap at floor level will fill with ash which is not a bad insulator. If using blanket be sure to use the type that is exonerated as a carcinogen.

i hope you have a large forest nearby to fuel your oven, you'll need it.

[jonv]

Glass??? I used ceramic fibre rope; just jammed it into the gap.

[Alomran]

What type of flexible low conductive material recommended to be used? Would it be sufficient to use glass in the 1/2 gap?

[david s]

The gap is not essential. It's primary function is really as a thermal expansion gap which reduces the tendency for the inner expanding oven to place stress on the cooler outer shell of the igloo and outer decorative arch causing unsightly cracks. For this reason the gap needs to be filled with a flexible low conductive material. If you are building an enclosure then this is less of a problem because you don't have an outer shell. However, it will reduce some heat flow by conduction, but because it's so small won't do much to stop heat flow by radiation. You wouldn't expect 1/2" of insulation over the dome or under the floor to prevent significant heat loss. In my build because my flue gallery is so light (10 kg casting) and therefore not a significant heat sink, my expansion gap/thermal break is between the flue gallery and the outer decorative arch.

[cnegrelli]

That gap is a thermal break, to keep the energy (i.e. heated dome) from dissipating the heat to the chimney/flue/entry area, where it does not good for cooking. This reduces the volume/mass of material that is heated up resulting in quicker charge times and keeps the heat from bleeding away quickly.

[Alomran]

I've finally decided that the outer door will be made of ceramic fireproof glass. When fully closed you can see the whole fire without the radiating heat. If the door is totally closed, two air vents, which take air from the outside of the building feed the fire from either side at the bottom of the vent area (see recess holes in picture). The glass will sit within a U shaped frame and will be removable. There will be a counter weight the same weight as the door which hangs inside the Inside the envelope/box. It will be a bit like how a sash window works, and enables the window to stay in any elevated position due to its counter weigh https://en.wikipedia.org/wiki/Sash_windowt. All this will be will be removable for servicing

What is the purpose of creating a 1/2" air gap separation between the dome and the doorway/chimney chamber structure?
Is it a thermal expansion gap?
Is it advisable? or a must to have?