28" homebrew cast oven in walled enclosure Belgium

[david s]

No, don't hose it, you don't want to get the underfloor insulation wet. Some of the water in the mix gets used up chemically in the hydration process, and for this to continue it needs a certain amount of free water to continue the reaction. It looks pretty good, just remove the sand tomorrow and cover it if it looks like raining. Once you've filled the voids keep it well covered for a week.

When you remove the oven mouth mould plate, use it to make the flue gallery mould plate, an inch larger all the way around. This ensures that there'll be room to fit your door in place.

You've just built your dome that would take the brick builders months to get to the same point, and it costs peanuts.

[Kris S]

Thanks for reassuring me David

Next question : I've been tinkering with the flue gallery mould, it's 23.7cm deep (9.3") for a 15cm (6") chimney, so I have 4.4cm (1.7") on either side.
It looks kinda deep, is it possible to reduce the depth by either:

* going even narrower than 4.4cm on either side,
* or by casting a bit more on top of the current oven mouth? is that strong enough, more likely to crack when heated? I could reduce the depth with 4.4cm that way (see second picture pls)

or just leave it as it is, because It won't be worth the trouble to gain 4.4cm?

note: chimney pipe is not the actual one I will use, and the mould isn't finished yet either.

[david s]

There is a stack of room at the top of the flue gallery to set the pipe further back. If you make it start even higher by funnelling the gallery towards the base of the pipe you will have even more room to set it back further, making the gallery entry even shallower. The funnelled gallery will draw better, producing a smoother smoke flow and the shallow gallery makes the oven much easier to work, moving things in and out of the oven chamber. Because you don’t need the thermal mass in the gallery it can be made thinner. Around 35mm should be plenty of strength.

[Kris S]

I'm not sure I completely understand what you mean, english is not my mother tongue...

I found this pic of one of your shallow flue galleries, I'd like to do something similar.
(here's the thread: https://community.fornobravo.com/for...lue-size/page2)




Trying to figure this out, is this diagram somewhat correct?
So you put the mould right up to the oven mouth, and the back edge of the chimney is also in line with the oven mouth to save space.
So the surface onto which the back cut out tab of the chimney rests is cast a couple of centimeters over (on top) of the oven mouth edge...?

If this is correct, I could shorten the flue gallery from 23.7cm to 15 + 3.5 = 18.5cm...

[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?

[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]

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.

[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?

[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]

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

[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...

[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.

[Petter]

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

[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...

[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...