28" homebrew cast oven in walled enclosure Belgium

[david s]

Time to throw in a chicken. Great work, you’ve done a nice job.

[Kris S]

Here's a pic of the apex starting to clear a little. That top log may look like it's too big for curing fires, but it's not, it's the camera angle and the oven diameter itself is just 70cm - 28".

I haven't yet fixed the definitive chimney, so used a 15" long 6" diameter pipe, and most of the smoke takes the chimney route instead of coming out of the front arch, pretty pleased with that.

I hope to have put a roof over the oven within the next 2 weeks.

[Kris S]

Just a quick update: yesterday I covered the dome with 3" of ceramic insulation and started the curing process.

I was really gonna try to go the slow way and try not to go beyond 150 C on day 1, 200 on day 2, 250 on day 3... but I found it difficult to maintain a 150 C fire. I ended up curing 6 hours around 200 C with spikes of 300 C.

after a while I saw steam and to help the steam escape I removed 1" of insulation but backed of in temp.

On day 2 I could see no visible cracks and tried to not go beyond 300 C. After a few hours around 250 - 300 C there was still no steam, so i thought I might as well push it a little harder to 350 C. Still no steam or cracks so I kept it at 350 for another hour or so.

a little later I noticed a small area at the top of the dome starting to clear. I took the temp and I spiked to almost 400 C

Still no steam, but immediately backed of.

Is it normal that I don't see any steam anymore on day 2 and that the very top of the dome is already starting to clear a little? The cast itself got 3 weeks to dry out....

At what internal dome temp does the dome becomes completely white, I.e. what's the final temp i should aim for?

[Kris S]

Mullster (Ha ! finally figured out how to do that)

Thank you, I'll start the 5-7 days curing fires tomorrow as we have just had 2 rain filled weeks , so I'll see if the cracks worsen or not.

In the meantime I've been busy with the decorative arch, I stole the idea from mesoiam: https://community.fornobravo.com/for...ge4#post425083

I used some brick splits, bedded them in mortar, added some wire mesh and rebar, covered it with concrete and added some loops of thick wire to tie the arch on to something later.

this weekend I plan to start building the enclosure, I'm gonna go with what I know and feel comfortable working with: wood instead of metal studs. I know it's considered a big no no but since I'll be covering the oven with 2" ceramic wool insulation and some left over rockwool on top of that, I'm confident I can avoid exposing any wood close enough to hot surfaces, we'll see...

[Mullster]

Kris S your build is looking great. I certainly didn’t achieve such a smooth dome as yours and I cracked my flue gallery too. I had to patch to some degree but honestly - 6-9 months on the cracks just don’t bother me. The oven works great too. If structurally it feels strong I would stick with it, but to David’s point, if you have the time and patience to re-cast...

[Kris S]

Well as long as it doesn't collapse when I fire it up in a couple of weeks I'm happy.

Aesthetics of the cast are not my concern as I will build something around it anyway...

[Petter]

Patch a couple of cm on the outside while the cast is still wet?!

[david s]

The cracks are not going to go away and squeezing some more homebrew into them will be extremely difficult and may not work anyway. Sieve out the coarse sand from your homebrew mix for filling voids and cracks. That makes it both finer and richer. You will have to decide whether to redo the casting or just build over it. They may never get any worse. As they say there are two kinds of oven owners, those who say their ovens have cracks and those who lie about their ovens having cracks.

The homebrew is so cheap the main cost is your time and casting is very quick. I bet you won't be stopping oven building after completing one oven.

[Kris S]

Turns out the flue mould wasn't so easy to remove, it was 90% of the way out and then I cracked it.

I immediately tried to patch the cracks using David S method of trying to press up the homebrew paste in the cracks, which was difficult because it's like a hairline crack...
Actually 2: one goes all the width of the gallery, visible both from inside and outside, and then there's a smaller one only visible on the outside.

Will I be okay, or should I butress to the sides of the gallery using some bricks (they will be conceiled behind a wall anyway so no big deal), I saw someone else use the same approach when he cracked his flue gallery...

[Kris S]

Fingers crossed for a smooth release of the pipe...

[david s]

You've got the idea. You can easily go quite a bit higher as well as moving the pipe further back to make the gallery shallower. In this way I've got the depth of the sides of my flue gallery down to 13 cm with a 125mm flue pipe.
If you are using the flue pipe to cast up against, remember to wrap some cardboard around it . This will allow the pipe to expand a little without stressing your casting then some sheet plastic around that for easy removal of the pipe once the homebrew has set.

https://community.fornobravo.com/for...775#post390775

[Kris S]

Could anyone guesstimate if this flue I put together is ok volume-wise so that the smoke would take this route?
Or should I make it a little higher still?

[Kris S]

Really pleased with how the inside of the dome looks, a couple of wrinkles but minimal patching up required in my opinion.
Note the cardboard 30cm - 12" pizza inside for size reference.

[david s]

If the gallery is made taller than your pics show, you can make it with plenty of volume at its base for smoke collection before it travels higher to the base of the flue pipe. You are correct in observing that mine is quite thin, but I don’t cast in situ using homebrew. I pre-cast using castable refractory (calcium aluminate cement) enriched with AR fibreglass fibres, ss needles and carbon nanotube ad mix (fibres on a molecular scale). I also have buttressing on the sides and over the top corners of the gallery. This allows me to make the gallery strong, but with a low thermal mass to reduce the heat sink effect. That’s why I suggested you go with a thickness of 35mm.

[Kris S]

Dug a little deeper in the forum and delved this pic from you David: https://community.fornobravo.com/for...ion#post398422

So I guess that confirms I can rest the partly rounded back edge of the flue on top of the oven mouth without having to fear cracking:

It does however appear there's a gap between the top of the oven mouth and the flue edge that sits on top, is this on purpose or necessary?

Also the thickness of the front part of the flue looks really thin, something like only 1-2 cm?