36" (900mm) Pompei build in central Sweden

[icrackracquets]

Have now started on the enclosure using 45x45 steel studs. I actually got the sheathing on and part of the roofing over the weekend but I don't have pictures of that yet.

Also made the first pizzas over the weekend. Worked great. I need to make a door over the winter so that I can bake bread the day after. I actually baked bread later in the night after the pizzas were done because the temperature seemed right. Turns out the floor bricks were a little too hot compared to the rest of the oven because the bottom of the bread is very well done. Not burnt, but very well baked.

[icrackracquets]

During curing fires I've seen no cracks in the dome or the entry arch. However, after the first pizza cooking session over the weekend I woke up the next day and found a crack in the entry arch.

I think I must not have filled in enough grout between these two bricks so it has 'collapsed' a little bit.

I'm wondering what people think about this. Is it worth the trouble of dismantling and fixing? Do I NEED to fix it or can/should I just live with it until/if it gets worse?

[david s]

https://community.fornobravo.com/for...-no#post460753

[mongota]

Take a close look at the top left of the arch, the white circle. Looks like a bit of separation causing a slight crack there when the arch dropped.

Also look at the base of each side, the red circles. The bricks sit half on, half off. I'd want to make sure there's no rotational moment with the brick spanning those two materials.

Additional support/buttressing seems required.

[icrackracquets]

Yes the base there was a planning error. I cast a 'lättklinker' base for the entry but then changed the design halfway through. However, I have poked and tested these repeatedly during construction and they're stable. I have permanent buttressing installed on the sides though. That's the wooden beams you can see on either side.

I haven't put on the sheathing for the front yet so I still have the option of jacking up this section of arch and shoving more mortar in there. I'm still debating if it's worth the effort or not.

[Toiletman]

During curing fires I've seen no cracks in the dome or the entry arch. However, after the first pizza cooking session over the weekend I woke up the next day and found a crack in the entry arch.

I think I must not have filled in enough grout between these two bricks so it has 'collapsed' a little bit.

I'm wondering what people think about this. Is it worth the trouble of dismantling and fixing? Do I NEED to fix it or can/should I just live with it until/if it gets worse?

On the funny side, you can now update your nick to IcrackArches ...

On the serious side: I don't think it's related to grout: it seems to be insufficient structural support of the arch. A half-dome arch has the least side thrust, you only have a section of an arch, as have I. I did some calculations on my design, and the amount of sidethrust and tipping moment these generate is quite astounding. I calculated with 750kg on top and decided to create buttresses, as even with half that load it would still topple. I'll probably try to reduce the weight on top of the arch as well.

How much have you calculated the strength and stability of your construction?

It seems like there's multiple possible issues with your construction:

• As mongota points out: the half-supported base seems to have allowed a little bit of movement or compression, allowing a small bit of rotation that 'cracks' the arch open. Mortar can't support bending loads, so it failed. Was that crack in the 'lättklinker' already there before you discovered this crack? Or did maybe that whole section got moved?
• The chimney loads are not distributed to the sidewalls, but put directly on the weakest point of the arch. The crack on the right seems to have failed on the last brick loaded by the chimney. It might be the angle of the picture, but is the chimney on top of the arch actually symmetric and perpendicular? It seems to be leaning to the right? How much additional load/moment will wind loads on the chimney put on your arch? Is it anchored in your roof already? Was it when it cracked?
• Your wooden supports might not have really been supporting the bricks yet, only now, with a cracked arch, and a little bit of movement or flex are they taking the weight. Did you pre-load these wooden supports in any way when you fitted them? Are you sure they can take the loads? How about in ten years when the screws have rusted and the wood rotted a little bit?
• Unrelated issue: but there seems to be a lot of blackening in the front of your gallery arch: maybe the inlet to the chimney is a little bit too small/square and it could benefit from a redesign.

It's easy for me to say, but I'd take it out and redo it properly, fixing above issues.
I'd probably be worrying about it collapsing on me or a guest one day when the oven is a little hotter than normal, the materials aged and corroded, and just a little bit of extra wind load on the chimney giving it the last straw....
Jacking it up and just slathering some extra mortar on is not going to fix any of the above issues.

On the other hand. Some suggestions for MacGyvering or troubleshooting it:

• First do your calculations on what it should theoretically have to take in load, and what it has taken practically already. If you are convinced it should be more than strong enough you could consider testing it. For instance by taking the chimney pipe out, and seeing if you can stack some heavy weight such as cement bags or sth on top of it... if it doesn't fail you can probably trust it for a while. However: this is a very risky operation to do if it would fail... so be very careful if you actually consider attempting it and take precautions for where the bricks would go if they would fail. I wouldn't risk such an exercise and would just take the pain of tearing it down and rebuilding. Especially since you are already dealing with a damaged structure.
• You seem to be building quite a sturdy construction around the oven. You could consider ways of supporting the weight of the chimney to the 'stiff box' you are building, by for instance steel cables to the corners or something like that.

Anyway, too bad to have such a setback, especially after all your hard work and all you want to do is enjoy very pricey pizza's... I wish you wisdom in dealing with it and hope you find a good way to fix it.

PS: on the topic that david s quoted it seems to be a full arch that is attached to the actual dome. This seems to have opened up due to the expansion of the dome and chimney, pulling the arch apart on its weakest point. However, it's still standing due to being a full arch and possibly being attached to the dome.
To me this seems different from your issue: I think your arch really suffered a structural failure. Basically your right side wall moved, and allowed the middle of the arch to slip down. That side wall still very much wants to move to the right, and if it ever does your complete arch will fail and drop down.
How is it supported on the back at the connection to the dome? Could it be that it's now resting on the dome and that's why it didn't drop further?
PPS: David has a lot more practical experience than me, so I might just be worrying too much here. Feel free to chime in again.

[icrackracquets]

On the funny side, you can now update your nick to IcrackArches ...

On the serious side: I don't think it's related to grout: it seems to be insufficient structural support of the arch. A half-dome arch has the least side thrust, you only have a section of an arch, as have I. I did some calculations on my design, and the amount of sidethrust and tipping moment these generate is quite astounding. I calculated with 750kg on top and decided to create buttresses, as even with half that load it would still topple. I'll probably try to reduce the weight on top of the arch as well.

How much have you calculated the strength and stability of your construction?

It seems like there's multiple possible issues with your construction:

• As mongota points out: the half-supported base seems to have allowed a little bit of movement or compression, allowing a small bit of rotation that 'cracks' the arch open. Mortar can't support bending loads, so it failed. Was that crack in the 'lättklinker' already there before you discovered this crack? Or did maybe that whole section got moved?
• The chimney loads are not distributed to the sidewalls, but put directly on the weakest point of the arch. The crack on the right seems to have failed on the last brick loaded by the chimney. It might be the angle of the picture, but is the chimney on top of the arch actually symmetric and perpendicular? It seems to be leaning to the right? How much additional load/moment will wind loads on the chimney put on your arch? Is it anchored in your roof already? Was it when it cracked?
• Your wooden supports might not have really been supporting the bricks yet, only now, with a cracked arch, and a little bit of movement or flex are they taking the weight. Did you pre-load these wooden supports in any way when you fitted them? Are you sure they can take the loads? How about in ten years when the screws have rusted and the wood rotted a little bit?
• Unrelated issue: but there seems to be a lot of blackening in the front of your gallery arch: maybe the inlet to the chimney is a little bit too small/square and it could benefit from a redesign.

It's easy for me to say, but I'd take it out and redo it properly, fixing above issues.
I'd probably be worrying about it collapsing on me or a guest one day when the oven is a little hotter than normal, the materials aged and corroded, and just a little bit of extra wind load on the chimney giving it the last straw....
Jacking it up and just slathering some extra mortar on is not going to fix any of the above issues.

On the other hand. Some suggestions for MacGyvering or troubleshooting it:

• First do your calculations on what it should theoretically have to take in load, and what it has taken practically already. If you are convinced it should be more than strong enough you could consider testing it. For instance by taking the chimney pipe out, and seeing if you can stack some heavy weight such as cement bags or sth on top of it... if it doesn't fail you can probably trust it for a while. However: this is a very risky operation to do if it would fail... so be very careful if you actually consider attempting it and take precautions for where the bricks would go if they would fail. I wouldn't risk such an exercise and would just take the pain of tearing it down and rebuilding. Especially since you are already dealing with a damaged structure.
• You seem to be building quite a sturdy construction around the oven. You could consider ways of supporting the weight of the chimney to the 'stiff box' you are building, by for instance steel cables to the corners or something like that.

Anyway, too bad to have such a setback, especially after all your hard work and all you want to do is enjoy very pricey pizza's... I wish you wisdom in dealing with it and hope you find a good way to fix it.

PS: on the topic that david s quoted it seems to be a full arch that is attached to the actual dome. This seems to have opened up due to the expansion of the dome and chimney, pulling the arch apart on its weakest point. However, it's still standing due to being a full arch and possibly being attached to the dome.
To me this seems different from your issue: I think your arch really suffered a structural failure. Basically your right side wall moved, and allowed the middle of the arch to slip down. That side wall still very much wants to move to the right, and if it ever does your complete arch will fail and drop down.
How is it supported on the back at the connection to the dome? Could it be that it's now resting on the dome and that's why it didn't drop further?
PPS: David has a lot more practical experience than me, so I might just be worrying too much here. Feel free to chime in again.

I calculated a lot before my build, but I did not calculate side thrust of the entry arch. I just added those wood butresses and called it good. I did not preload the buttresses at all so that could definitely be a factor. However I did wiggle them on each side after the 'collapse' occurred and I could swear they were both still not super tight against the arch, but I think I should check that again.
Likewise, I'm fairly certain the chimney is mostly straight and what you're seeing is just a result of picture angle. I should check this again though as well. When the collapse occurred I had not put on the roof sheathing. Now I have and the chimney is now braced by the roof.

While jacking and grouting might not fix it, it seems like jacking and loading the buttresses might help. That's going to be the most likely course of action this year at least. Probably might try bracing the buttressing to the enclosure frame as well as a safety/ageing precaution. There is no way I'm taking entire arch and chimney down and redoing it before winter. I think my wife is close to her limit with my work on the pizza oven. Especially consdiering I still don't even have the enclosure finished.

The blackening of the entry is almost entirely from the curing process. I read a lot about this during curing because I was also worried about it. It seems extremely common that wet/new ovens smoke a lot out of the front. It is my hope that this will improve with age. I definitely don't have the energy to completely redesign the entry. Luckily it is just the entry and as I have built the entry completely separate from the dome, it is able to be redone a few years down the road without affecting the actual dome. I built the entry with a ~10mm gap from the dome. I glued a piece of fire rope around the perimeter as a small insulation. So the entry is just butted up against the dome.

[icrackracquets]

So whether it was a good idea or not, I have no idea, I attempted a fix on the entry arch. I took the form I used and cut it in half so that I could fit a jack under it in order to get an even load/support distribution. I jacked it up slowly to get it back to the right height, loaded the buttresses, and dropped the jack again. It seems to have worked. At least enough to not need to worry about it for awhile. I also added some braces anchoring the buttresses to the side walls of the enclosure as a redundancy.

After two full temp cooking there is definitely still smoke coming out of the entry. But my oven walls also don't completely clear under a full temp fire (just the dome) so I'm hoping it's still just a slightly wet oven. So hopefully once it's fully dried and the entire oven routinely clears this issue will start to resolve itself.

Until then I think I'll just make a metal blast door to fit in the outer arch in order to keep the smoke in. Also need to make a heat retaining door over the winter so I can get some bread going.

[UtahBeehiver]

New ovens are notoriously smoky. It takes a while to get all the mechanical water out of the build. Each fire it will get a little better. Be sure you are drafting up the chimney well before fully loading oven. I usually start my fire under the chimney then when drafting good push the fire into the middle of the dome. Clearing takes place around 900 F and works it way down the sides of the dome, if you see a ring of carbon near the bottom that means the floor area still has moisture in it.

[david s]

New ovens are notoriously smoky. It takes a while to get all the mechanical water out of the build. Each fire it will get a little better. Be sure you are drafting up the chimney well before fully loading oven. I usually start my fire under the chimney then when drafting good push the fire into the middle of the dome. Clearing takes place around 900 F and works it way down the sides of the dome, if you see a ring of carbon near the bottom that means the floor area still has moisture in it.

Further to that very good advice, as the unburnt carbon indicates moisture, there is a huge difference in temperature between the crown and the black sides. This also means a huge difference in thermal expansion. It is the difference in thermal expansion that creates stresses and sometimes cracking. Moisture in the bricks or refractory will hold back the temperature. If you have an infrared temperature gun you can read these differences in temperature quite easily.
It is precisely at this stage when the problems can occur. Unfortunately it is also at this stage when first time oven builders get impatient and increase the viciousness of the fire. Under NO circumstances should you use a blast door to increase the chamber fire intensity at this stage. Some folk use a blast door to reduce the heat up time. It works by reducing the air (oxygen) intake to the ideal fuel to oxygen ratio. However, if used before the oven has become heat soaked and the bricks or refractory pretty much evened out, it leads to the same problem of uneven thermal expansion which creates micro cracking that is not even visible
As an example, potters limit their biscuit (unfired clay) firings to 100C/hr to avoid cracking. The same applies to fired bricks or refractory to a lesser extent. Some potters will fire their glaze firings at 250C/hr and while the thin walled biscuited pots will handle it the thick bricks are being placed under a lot of stress. Most oven owners ramp up their ovens from ambient at a rate of 300C/hr even when their ovens are dry. A slow heat up is far kinder to your materials and leads to a much longer life of your oven.

[icrackracquets]

Further to that very good advice, as the unburnt carbon indicates moisture, there is a huge difference in temperature between the crown and the black sides. This also means a huge difference in thermal expansion. It is the difference in thermal expansion that creates stresses and sometimes cracking. Moisture in the bricks or refractory will hold back the temperature. If you have an infrared temperature gun you can read these differences in temperature quite easily.
It is precisely at this stage when the problems can occur. Unfortunately it is also at this stage when first time oven builders get impatient and increase the viciousness of the fire. Under NO circumstances should you use a blast door to increase the chamber fire intensity at this stage. Some folk use a blast door to reduce the heat up time. It works by reducing the air (oxygen) intake to the ideal fuel to oxygen ratio. However, if used before the oven has become heat soaked and the bricks or refractory pretty much evened out, it leads to the same problem of uneven thermal expansion which creates micro cracking that is not even visible
As an example, potters limit their biscuit (unfired clay) firings to 100C/hr to avoid cracking. The same applies to fired bricks or refractory to a lesser extent. Some potters will fire their glaze firings at 250C/hr and while the thin walled biscuited pots will handle it the thick bricks are being placed under a lot of stress. Most oven owners ramp up their ovens from ambient at a rate of 300C/hr even when their ovens are dry. A slow heat up is far kinder to your materials and leads to a much longer life of your oven.

Interesting. The purpose of the blast door was simply to stop smoke escaping out the front. But if the side effect of that is a super fast heat up time I suppose I'll wait on that for a bit.
I've only done the two cooking fires now and to get up to temperature I built up over three hours. Mostly because I've never cooked like this before, I knew the oven was still new/moist, and I wanted to make sure I'd have enough time to get it up to temp. Looks like I'm keeping that schedule for the next few fires at least until I can clear the entire dome. I still haven't seen any cracks yet (except for the obvious entry 'collapse') but I'm only seeing the inside and I obviously couldn't see microcracks.
Thanks!

[david s]

Smoke is unburnt fuel, so try not putting so much in the chamber.

[Gulf]

Also, extremely dry wood works best in a WFO.. Even limbs that have been cut for a year still have a lot of water in them. The wood won't burn well until the water has been driven out. Water can be another cause of incomplete combustion in even in a dry oven. I like to dry my limbs/split wood for a couple of years or more. I haven't always been able to do that. Dead fall limbs and trees is another source for dry wood. In many cases the limbs have stayed attached to the tree for a couple of years before it is fell by wind. Even if it has received a recent rain, deadfall only takes a month or two to become dry enough for oven use imo.

[Giovanni Rossi]

A couple more wood comments: The experienced fellows on the Forum recommend using wood "no thicker than your wrist". That has been a good gauge for me. Sometimes I try to do other things during the start up and get complacent. If I lose the flame, there's always some smoke before the new wood ignites on the embers. Also, when bringing my oven up to temp, I'll stage the next pieces in my entryway. That gets them nice and toasty before they hit the flames.

[rsandler]

Yet another good way to get dry wood is to toss several logs into the oven after the fire is out and the temps have dropped below 400F/200C. Kiln-drying, effectively. With my first oven, we were living on the East Coast of the U.S., where it was very humid in the summer, such that thoroughly seasoned wood, or even commercial kiln dried, would be damp and smoky after a week or two of sitting in my garage. I could only get a quick, clean fire if I made a point of drying the next-week's wood with the residual heat from the previous week's fire. I can be a little looser now that I'm in northern CA, where the humidity is near zero and it hasn't rained since April :-).