2024 Neapolitan oven build

[david s]

Apart from the water resistant calcium silicate board which I’ve never seen or used, the standard cal sil, 5:1 vermicrete will suck up any water into itself just as much as blanket will. The good news is that when any of them are dry they just go back to their original condition. The one that I’ve found that does not is mill board. It turns to mush and is very weak when it’s dried.

[daidensacha]

Calcium Silicate floor insulation coverage

I was watching another youtube build of a precast Forno Bravo oven, and the guy mentioned it is good to extend the calcium silicate floor insulation so that the insulation blanket covering the dome comes down and stops on top of it. If there is water this will prevent it wicking water up the dome.

Is it necessary? In nearly all the builds I have seen where the soldier course is laid on the calcium silicate board, it is cut inline its where the outside of the dome meets it. Then the blanket and vermicrete is added, but I haven’t heard this mentioned or seen before.

I do have enough calcium silicate board, if I am crafty and stick the off cuts here and there. I’m wondering how others who make ovens do it?

Example of the calcium silicate board extending past the outside of the dome under the fire blanket covering the dome.

[daidensacha]

2 x 3000x50x1.5mm V2A 1.4301 Stainless steel bands delivered yesterday, along with bricks, insulation, mortar, plaster. Moving on with the original plan to attach the stainless steel bands with bolts and angle.

Thank David for the info. Spoke with my wife’s brother who is an engineer, he concurs with your opinion on not needing springs. I’m not sad about that.

My brick cutting jig is ready to weld together, all the parts are there and prepared. Once they are together I can measure for fixing holes that will fix the angle of the brick for the individual courses. Those holes will be the pivot from which the jig will move the brick to make left and right cuts and the precise angle for the course radius.



Once this is done I’ll complete the adaption for the wet cutting saw platform.

[david s]

As I’ve said previously, The expansion issue is probably not something you need to worry about and the amount is around half that of a kiln. You are correct in concluding that the bricks will expand tight against the band and then as it heats and expands the pressure is relieved and the reverse probably occurs on cooling. However relieving this variable tension with springs, although in principle may sound like an ideal solution, could be introducing further problems. The use of steel rods and nuts is the common method for kilns and I’ve never seen springs used although I’m sure if it were a problem someone would have tried it and you’d see it as a common method. Most electric kilns just have an outer sheet steel skin to hold the bricks in position. Cheaper ones that don’t have stainless often rust out well before the bricks are worn out. I’ve got plenty of expensive insulating fire bricks from old rusted kilns.
The expansion at 500c is not really a big problem, only around 3mm so probably not worth worrying over. Using springs may work, but I wonder how they’d look in 10 years time, particularly as they won’t be stainless?
The first oven I built had a problem with the door. I thought I’d be clever and made the door first with a wooden face and a cast insulating panel(using crushed insulating fire brick as the aggregate for the mix. In order for the door to release from the opening I made the door with a slight conical edge so it would fit and seal nicely against the oven mouth.placing some plastic around the door edge so the dome casting mix would release nicely when the dome casting was placed over the door. The door ofcourse removed beautifully, but on firing if the cool door was fitted to the hot kiln, on cooling it jammed so tight that the door became impossible to remove easily without damage to either it or the oven mouth. A few millimeters can create a big problem. Obviously I abandoned this type of door for future ovens. With the thousand of years oven oven building history and probably millions of variations and solutions to problems I should have realised that this solution must have been tried many times before and like mine, found to be unsuitable.

[daidensacha]

I found some examples of springs, one takes 200kg, the other 300kg. They would be attached to angle at the arch, with insulation between them and the dome, so protected from any significant heat. Question is what sort of pressure would be sufficient force to reinforce the dome? That would allow expansion/ contraction, and the pressure would remain pretty constant.

[daidensacha]

david s The feedback is good, and appreciated. It can only help me to understand and pushes me to research. It’s a rabbit hole I hadn’t anticipated, but I’m committed so let’s go.

To come to the right answers I need the right questions.

Firebrick expansion

How much do firebricks expand when heated to 500C?

• The first obstacle to getting relevant accurate info is that it depends on the type, brand, and materials used in the firebricks.
• Searching through information via Google, i came across a white paper with an interesting statistic. The thermal expansion of a 150mm firebrick at 500C was .254mm. At this rate, with a dome that approaches a circumference of 3 meters, it extrapolates to 5mm expansion.
• The unknowable for me is the temperature distribution in the brick, from the inside exposed to the fire which would be hottest, to the outside of the dome which would presumably be less.

V2A 1.4301 Stainless Steel

• Some data on its qualities. Austenitic (non-magnetic), low thermal conductivity (heat resistant), corrosion resistant.
• Has a high module of elasticity at 200 GPa. (see Elastic Modulus: Definition, Values, and Examples for explanation of module of elasticity)
• Coefficient of thermal expansion 16 K-1 · 10-6 (this was not in my schooling. doing my head in calculating it for 3000mm long strip, get varying result from 12-25mm @460C)

From reading, it’s clear both the bricks and stainless expand, but to different degrees and at different times due to the differing rates of exposure to the heat.
If my calculation is anywhere near the ball, then the stainless steel would expand slightly more than the firebrick over a 3 meter length. Enough that when the oven is heated, there would be less reinforcing tension translated from the stainless band to the oven dome.

Open to any input if someone has more education about these terms and what it means.

It did come to me as a possibility to add a high tensile spring into the band mechanism. Then enough tension could be added that the spring would allow for expansion and contraction, albeit the reinforcing strength would then also differ, it would possibly be a way to eliminate any slack in the band when the oven is at full heat. Thoughts?

[david s]

It is common for brick kilns to have some steel bracing. During firing thr refractory material (bricks) will expand from the heat well before any steel bracing, but as the temperature climbs and the steel begins to expand, sometimes there needs to be some adjustments by tightening the bracing. As the kiln cools the steel bracing starts its shrinking and should be loosened again to the original position. Kilns generally reach more than double the temperature of a WFO, and therefore double the thermal expansion. , but the same principles apply.
For most steel braced ovens the adjustment is not possible because the adjusting nuts are probably deeply embedded in insulation.
This difficulty does not present itself for an oven built as a hemisphere, because its form is far more stable and self supporting. The other big advantage of a hemisphere is of course its superiority as being the most efficient chamber for even circulation and therefore economy. Kilns built in a cube formation are much better to load wares into, but end up with cool spots in the corners. Bread ovens with a square or recatangular chamber with a low roof hold more bread and are easier to load than a circular or hemispherical dome.These are usually considerations for commercial ovens rather than those for home owners.

I'm not trying to frighten you away from your plan, but just be aware of the extra work you have to go to as well as overcoming some problems that may occur.

Check back here

https://community.fornobravo.com/for...137#post457137

[daidensacha]

I gave up the dream of building a true Naples brick oven, but I'm still interested in seeing others do it. My questions is how the stainless band(s) that hold/buttress the solider course deal with the expansion can comes during firing. I once saw a precast oven on a trailer where the builder had accidentally made the metal straps that crossed the oven to keep it from sliding off the trailer too tight. You could actually see the oven dome trying to expand upward and then being squished outward then it was fired. Or at least that was what it looked like.

How do builders deal with that.

And congratulation on the great work so far. It's all very thoughtful.

Thank you. All my work to date has been in sketch-up, and google. But it’s been a great process, refining, changing, building it virtually over and over again. It’s helped me to understand what’s needed, and how to tackle details that had me stumped, like the arch. This still evolves and changes, and when I make one change often it cascades to other aspects so I need to alter other parts of my plans.

I first came across Forno Bravo plans around 9 years ago, and it’s been my dream since then to build an oven. I decided this year to take the jump and “do it”. I’m no expert, far from it. There are many others in this forum who have far greater knowledge and experience with these ovens.

I did read about expansion of the firebricks. If I remember correctly, nature of the material is such that it is minimal. The greater stress I am worried about is the weight of the dome on the soldier course. I am laying them directly on the insulation board, without cementing under them as that isn’t really possible on the insulation board. I also read it shouldn’t be anyway, to allow movement and expansion, which will stop the reduce the possibility of cracks.

I don’t imagine the reinforcement strap should be tensioned with a view to stopping expansion, but from my view a potential explosion of the soldier course outwards from the downward pressure of the weight of the dome. My brother in law is an engineer, so i’ll lean on him for advice about the the required tension. It’s a good point you raised though, and i’ll be mindful when it comes to tightening the bands. Still a little way off, will start excavating a 9000x5000mm are for a terrace come outdoor kitchen. The pizza oven will be in one corner, with 2 meter bench on the left, and 3 meter bench on the right with a fireplace and grill. It’s still cold, too cold to lay the slab, but I can prepare the foundation and formwork so I’m ready as soon as there is a good patch of warmer weather.

[totalnewbie]

I gave up the dream of building a true Naples brick oven, but I'm still interested in seeing others do it. My questions is how the stainless band(s) that hold/buttress the solider course deal with the expansion can comes during firing. I once saw a precast oven on a trailer where the builder had accidentally made the metal straps that crossed the oven to keep it from sliding off the trailer too tight. You could actually see the oven dome trying to expand upward and then being squished outward then it was fired. Or at least that was what it looked like.

How do builders deal with that.

And congratulation on the great work so far. It's all very thoughtful.

[daidensacha]

rsandler Thanks, I’m moving forward with my plan to build the brace reinforcement out of V2A Stainless steel.

I picked up 4 x 100mm lengths of x50x3mm flat V2A stainless steel, and 4 x 40mm lengths of V2A 25x4mm stainless tube yesterday. Called into a local engineering workshop today and they were more than happy to weld them together for me.


All tthe other pieces are on the way.
1 meter M16 A2 stainless threaded rod, with washers and nuts. ( I will cut this into 4 x 250mm lengths, or shorter, once I know what’s needed.)
2 x 3000x50x1.5 V2A stainless sheet strips.

This will last my lifetime.

All I have to do is drill the holes, and join the bands with solid stainless rivets. But I’ll leave that until when I have the dome and arch up, and know the exact measurement I need to fix them. Having a plan with the details worked out puts me at ease.

[rsandler]

I can't speak for the exact temperature on the outside, as I've always had my ovens insulated before going to full cooking temperatures, but I have never gotten the lower dome walls on either of my ovens (both hemispheres) above even 500C on the inside. The inside will generally be hotter than the outside, so surely we're talking lower still for outside temperatures. The peak of the dome will definitely get above 500C--can't say exactly how high as my IR thermometer only goes to 550C--but the lower walls are always cooler. I'd defer to others like David S if they think differently, but would think that a material resistant to 600C would be just fine banded around the lower part of the dome walls.

[daidensacha]

Oven Dome Temperature and reinforcing band material

In theory I understand my goal with the oven is to heat and cook at 500C. This is purely conceptual for me as I have no experience yet heating an oven with wood, and cooking in one at those temperatures.

I also understand the quantity of wood required, and therefore heat up time is relative to the oven size and thermal mass that needs to heat up to temperature. That said, in choosing the correct material for reinforcing bands for my oven, what I need to consider is the temperature the metal bands will be exposed to. V2A, or 1.4301 stainless is heat resistant up to 600C. WIth its anti corrosion properties it would also be resistant to rust from any accumulation of moisture in the dome.

Bear in mind placement of the reinforcing bands around the outside of the brick dome. I wonder if someone with experiential knowledge can share with me what temperature they would be exposed to sandwiched between the firebrick some and the insulation blanket? I’m not sure if I need to look for something with resistance to higher temperature.

[daidensacha]

Neapolitan dome reinforcement

David kindly brought this to my attention, that because of the accentuated curve of the Neapolitan style oven, it requires additional reinforcement of the lower soldier course. I have a clear idea of what needs to be done, see images posted by David a few posts before this one. See also in the images provided for oven build in Napolitian style 106cm build inside a hobbit house.

This sent me down a rabbit hole. I’ve spent countless hours researching, googling trying to find similar applications of this type of reinforcement to see if I can buy some stainless steel bands. I came across 2 example where it is used. Reinforcing walls of old water tanks, and hot tub hoops. In the US, it might be easier to get hot tub hoops made to order. Here in Germany not, but I did find a hot tub complany in Estonia that would gladly make and send them to me in Germany.

I‘m no expert with steel, but I found out in Germany V2A Stainless steel (also known as 1.4301), or V4A stainless steel (the newer version) is rustproof, heat resistant to 600C, and easily welded using all electrical methods. It is relatively inexpensive too when I contacted a supplier to ask about the price of 2 x V2A stainless steel bands 3000 x 50 x 1.5mm.

I‘m making brackets similar to what is used in the Napolitian style 106cm build inside a hobbit house. I will connect the band to the brackets with solid stainless steel rivets. The Bands will be secured to the front of the oven with M10 bolts anchored to angle at the arch.

I‘m just documenting this in case someone else also needs information about bands and what to use, or where to get it. I‘m going this route as it is by far the most inexpensive, and will give a good result. Hot tub hoops would also work, if your somewhere where you can get them.

[david s]

The products you referenced are mortars and are not likely to be suitable. Get a bag of dense castable refractoryy. It contains calcium aluminate cement which is more heat tolerant than ordinary Portland cement OPC, high temperature aggregates and burnout fibres which reduce the risk of explosive steam spalling.

"I’m not sure what temp it gets in the vent," Put it this way, the black soot in my flue gallery never burns off and that happens at around 300C. OPC starts to degrade north of 300C, but to be safe castable refractory would be a safer choice for your flue gallery

[daidensacha]

I was exploring using it to cast a light weight vent between the top of the arch and the flu. See image dotted lines. I just found out I get a 5% rebate for signing up to emails from the supplier I’m getting my materials, so I might just spend half that rebate on 25kg of castable refractory.

I’m not sure what temp it gets in the vent, but far from the temp of the dome. I think it would stand the heat there. The structure of the chimney will be built around it. The harshest treatment it might get will be when it gets cleaned.