31"/800mm in Eindhoven, the Netherlands: Design critique and build topic

[david s]

Well, two days spent well, but the vermicrete will be finished next Saturday... I didn't have enough 10:1 mix to fully close the dome. In the end that was ok, as for the final part I first had to figure the chimney out first anyway... Not sure if it's fully according to your design david s , please let me know. I wrapped the whole chimney and adapter part with two layers of chicken wire, and then filled it all in with 6:1 vermi/perlcrete. You also mentioned putting refractory castable, but I'm not really sure where I should put it? Do you only do a thin layer of vermicrete and then a thick layer of homebrew around it?

Please see the pictures.

I'm not 100% sure what you've done here. I thought you were creating a sleeve, that I detailed previously, so the flue pipe could be removable. It looks like you didn;t do this and have surrounded the flue pipe seating with the 5:1 vermicrete. Because as it appears you have a double flue pipe, If that is correct, you do not want any kind of homebrew or cement render reinforcing around the inner pipe. I would be better if you extend the vermicrete around the inner pipe up to the base of the outer pipe as the same diameter as the outer pipe. (as shown in attached sketch) Then you can then more safely render over the vermicrete and around the outer pipe, but I'd still be leaving a small gap (5mm or so that can be filled with high temp silicone because the outer pipe at that position gets pretty hot.

[Toiletman]

I'm not 100% sure what you've done here. I thought you were creating a sleeve, that I detailed previously, so the flue pipe could be removable. It looks like you didn;t do this and have surrounded the flue pipe seating with the 5:1 vermicrete. Because as it appears you have a double flue pipe, If that is correct, you do not want any kind of homebrew or cement render reinforcing around the inner pipe. I would be better if you extend the vermicrete around the inner pipe up to the base of the outer pipe as the same diameter as the outer pipe. (as shown in attached sketch) Then you can then more safely render over the vermicrete and around the outer pipe, but I'd still be leaving a small gap (5mm or so that can be filled with high temp silicone because the outer pipe at that position gets pretty hot.

Thanks for chipping in David. Below is a sketch of what I did, hope it clarifies it a little bit.

I have a double-walled pipe, and have built the sleeve as you sketched before to make it removable. Your sleeve has tabs on the bottom to fit into the castable, but I'm not sure if you also used tabs on the top to actually hold the pipe, or if you do that just on friction? I also put tabs there, to make sure the pipe always gets back to the same position.

Some questions:

• The double walled chimney pipe is now supported on the inner pipe, on the tabs in the adapter. My feeling is that it would be more robust to support it on the outer rim of the outer pipe. I'm not quite sure if supporting it on homebrew castable there would be a good idea: it's a pretty sharp/thin ring, so I'm thinking over time it will cut and wear the homebrew. Maybe better to use a stainless steel ring or put some ceramic mosaic tiles there to actually provide the support?
• How to deal with the void? My feeling is that it's best filled with some insulation material such that the heat won't escape there. Ofcourse it would still need a gap to allow the pipes to slide in, and expand while hot. Therefore I'm leaning towards using vermicrete... probably the more high strength mix, possibly covered with render later? Any tips/idea's?
• You mention that the outer pipe gets pretty in your sketch. I'm not really understanding why? The whole purpose of having a double walled system is to ensure the outer pipe does not get hot right? Hence why I want to fill the void as that's currently the path where heat could escape to the outer pipe.

The damp curing is now done, so I've removed all covering from the oven. Now chopping wood to start the first small curing fire tonight... looking forward to babysitting it with a beer in hand and seeing if the chimney and steam escape paths work as intended.

Attachached also a view from the gallery looking up. I've since removed some of the excess vermicrete that came through the holes for the tabs in the adapter.

[david s]

It looks like yoi have a pretty workable solution.
Regarding your questions
I have three little tabs on the bottom of my sleeve adapter. You can see them in the first pic, but it's upside down so they are at the top.the tabs in the middle prevent the sleeve from dropping into the gallery and the cuts in the bottom of the pic show how I locate the sleeve in the gallery and surround it with some homebrew. The second pic shows how this arrangement works (the right way up) also showing the plastic which makes removal of the inner pipe after adding the homebrew around the sleeve, easier.
The third pic shows an oven with a double flue with the outer pipe seating on the terra cotta cap that sits around the inner pipe (although this one does not have a sleeve for inner pipe removal). If you want to be able to remove both pipes, you will probably need to use some long stainless screws to join both pipes at the top and the bottom.
Regarding heat in that area, yes it does get hot there, it's not very far from the flames that just lick around the top of the oven mouth and into the gallery. After an hour or two of firing you can't hold your hand on it. But up at the top where the outer pipe is fixed against the top rafter of the pergola, it's quite cool. I have blanket stuffed in between the two pipes both at the top and at the bottom for correct location as much as heat prevention. You will probably find yours is much the same once you crank it up.

[Toiletman]

It looks like yoi have a pretty workable solution.
Regarding your questions

Thanks David, that clears some of the uncertainty up.

Then for the oven progres: I lit the first curing fire today! And like so many others before me.... it went to hot and cracked the entry arch :-/. Oh well, it doesn't affect the oven function and all ovens have cracks right?

For the curing scheme I went with the firebrickco's recommendations of a 200x200mm fire x 3 hours the first two days, and then slightly going bigger in the coming days. I asked chatGPT to summarize the forum's curing scheme and got:

for all days: 6hrs at temperature:
1: 150C / 300F
2: 170C / 350F
3: 204C / 400F
4: 232C / 450F
5: 260C / 500F

It was quite difficult to keep the temperatures at 150C/300F, especially while also trying to keep the fire going. Typically it was more towards 170C / 350F, which is probably one of the reasons for the crack in the entry arch to appear: Uneven expansion of the dome due to the too large temperature gradients.

One cool thing to notice: the extension of the mosaic tiles under the ceramic blanket does provide a path for steam to escape. There was noticeably warmer air flowing from the weep holes underneath the oven.

Also: the chimney seemed to work well enough. It was a pretty windy and sunny day today, but the gallery arch is still not blackened at the front. Most smoke went up the chimney.

Enjoy the pictures, I'll keep firing tomorrow. All in all great milestone to enjoy with a beer in hand, tending the fire.

[UtahBeehiver]

There are those who say their ovens never crack and they also sell used cars too..... That said, lesson learned about going too fast and hot during the curing stage. Turtle wins the race over the rabbit during this phase of WFO construction. A crack in the arch is fairly common and the arch is self supporting so no structural issues there. Enjoy the oven.

[atak]

Netjes gedaan hoor, Ik benijd je zorgvuldigheid en je vaardigheden in 3d tekenen.

Well done, But The italian way is easier building the dome.

https://www.youtube.com/watch?v=pXrQ...oklynPizzaCrew the first 40 seconds

[Giovanni Rossi]

Toiletman , A little late for you, but for others following your progress...

I found some small heavy gauge wire baskets (origin unknown) at my parents house. I used 3 and made small fires with strips of wood and charcoal briquettes. That kept me from adding too much fuel and the hot charcoal ignited new wood. The baskets allowed me to move the fires around to expose different parts of the dome to the heat and not over heat one area too much during the early drying stages.

I was (visible) crack free for quite a while. I think it was the 6th or 7th full firing that I noticed a vertical crack in the dome starting about course 5 and climbing 3-4 courses at about 10 o'clock relative to the floor. As most report, it opens when the temp exceeds 1000 F and closes as the oven cools.

You may have had a crack no matter how you did the drying fires. I believe the variation in the bricks and their positioning plus differences in thickness of the mortar joints, all when subjected to heat, creates stresses in ways that crack locations will be predicted only by sophisticated AI modelling.