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28" homebrew cast oven in walled enclosure Belgium

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  • Kris S
    replied
    Laid the oven floor, tried my best to somewhat level the firericks, this is the best I could.
    They're not quite exactly the same dimensions, hence the gaps between some bricks, hope it's good enough.

    I'm also going to slightly narrow the oven opening from 48 cm to 44cm to prevent too much heat loss.

    Can't start casting yet for another week because delivery of the fireclay is delayed, again.

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    Last edited by Kris S; 04-19-2021, 12:58 AM.

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  • Kris S
    replied
    Thanks for your advice Ronstarch! allright I'll stick to the sturdier design then.

    Yes, I'll be casting over a sand dome, and casting the flue gallery separately. It's the big flexibility that that makes me a wee bit anxious for the moulds, I feel the easy work is done and now the hard part starts.

    The door opening, your oven is 1" wider and your door 2" narrower than what I plan (29" & 17" VS. 28" & 19").
    I've still got 2 weeks to decide the final width, not 100% sure yet. the oven will be mainly used for pizza's, but I'd also like to use it sporadiacally for some meat or fish dishes, and the remaining heat for some bread maybe. Can you not retain the heat inside longer after the pizzamaking by shutting the door when there's only embers left (i.e. no more smoke and need for the chimney?)

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  • Ronstarch
    replied
    Great progress so far! My opinion, yes, that first design is too fragile, you (or more likely a friend) will chip those tips away with your peel, and they could also just crack from heat cycling. The second way is stronger and better. Are you casting over a sand dome? If so, you basically have infinite flexibility as to how to cast that section of the oven, and if you cast the flue gallery separately, you have flexibility there as well. So there are ways to get creative to keep the flue gallery short while not creating any weak points. Something that I wish I had done on my oven is to have the vent start out wide and thin, venting back over the top of the dome itself, and then have the chimney set back from the front of the oven, as a way to keep the flue gallery shorter. Maybe something to look into. Also, by eye, your door opening looks pretty wide relative to the oven diameter. It’s an inherent inefficiency with smaller ovens, but you’ll lose a good amount of heat through that opening. But the trade off is nice easy access to the inside of the oven, which makes for a good user experience. My door is 17” wide on a 29” ID oven, which works well for me.

    Looking forward to the rest of this build!

    Edit: I’m an enthusiast who has built 4 homebrew cast ovens, mostly using the guidance from this forum. So, very far from an expert
    Last edited by Ronstarch; 04-02-2021, 08:30 AM.

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  • Kris S
    replied
    I'm in need of some advice here:

    would this first floor plan (on the multiplex board) work? It allows the flue gallery to be approx. 5cm shorter but i'm afraid the rebate/corner for the door may be too fragile and prone to breaking?

    Or do I stick to the more conventional design that I drew on the concrete slab?

    looking forward to some opinions!

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  • Kris S
    replied
    Forgot to add I also drilled three 10mm weepholes through the conrete, I could immediately see it's advantage as there was a little water seeping through after I put the Vcrete on.

    Getting way ahead of myself again and stocked a bit of future firewood under the oven.
    I've got a sheer endless supply of willow and oak, but read that fruit woods are considered excellent for cooking with. I have a little bit of apple and plum (close up picture) and also stocked some cherrywood.

    I intend to only use these if and when I get the hang of firing and cooking half decently.

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  • Kris S
    replied
    Poured the 10cm (2.5") thick 50/50 vermiculite/perlite insulating layer.
    Used a 5/5/2/3 volume mix of verm/perl/cement/water. Dry mixed the solids first before adding water as advised on the forum.
    Vermiculite is the brown stuff, and Perlite the white lumps in the picture of the wheelbarrow.
    Have to let it dry for 3 weeks now before continuing.


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    Last edited by Kris S; 03-29-2021, 12:39 AM.

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  • Matthijs
    replied
    The chimney is tricky.... I think the tabs in the end of the flue pipe give you a bit more stability (at least this worked for me. But also more touch point with the oven and risk of cracking the stucco.

    The photo shows my nice cracked stucco (one layer) in the front of the oven chimney. The stucco does not touch the chimney in any place.
    (I had to redo my stucco on the chimney anyway due to unremovable cardboard....)

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  • david s
    replied
    6” (150mm) is the correct diameter for your oven. The height doesn’t matter as the flue is only there to get the smoke away from your face. The taller the flue the greater the draw.if it’s really high it requires stays. Generally around 3 ft works pretty well without stays. I use one 900mm length for most ovens.

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  • Kris S
    replied
    Thanks David S for confirming the type of PP fibres I found are the right ones!

    Something else: I read somewhere (can't remember where anymore) that the length of the chimney should be about 3 to 4 times the door height.
    For me that would be 3 or 4 times 22cm, resulting in something like 70 - 80 cm.

    I realize the longer the chimney, the better the draft / less smoke escaping throught the front opening, and it also depends on the diameter, wind etc. but just wondering what you guys think of this. would 70 - 80cm be enough in your experience?

    For my 28" / 70cm oven I think a diameter of 6" / 15cm for the single wall chimney would do.

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  • david s
    replied
    Originally posted by Kris S View Post
    I also dropped my tape measure in one of the hollow colums of stacked blocks
    Sorry, can't help you

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  • david s
    replied
    The ones I use are Sika PPM 48/19 and come in a pack of two types of fibres, the short ones 19mm are finer than human hair, the longer thicker ones are 48mm and around 0.7mm. Only the fine ones should be used as burnout fibres. Sounds like you have the right ones. You can test them out by placing a pinch of them on a saucer and pop it into your kitchen oven at 180C. They should melt at 160C. You can use the larger fibres in a normal concrete slab. being plastic they don't corrode if on or close to the surface like steel fibres do.

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  • Kris S
    replied
    How long do the PP fibers need to be?

    The ones I found online are about 1/2 inch long and 20 µm thick.

    The same manufacturer (Sika) also makes about 2 inch long and 0.7mm thick fibers, but I can't seem to find a seller...

    Will the short ones do the job?

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  • Kris S
    replied
    I’m thinking a few steps ahead now, but for some reason I can’t wrap my head around how to place the chimney pipe on the flue gallery.

    I want to go the David S route with simply resting my (single walled) chimney on top of the flue pipe and rendering up to it (with a cardboard spacer in between) with Vcrete.
    But I don’t really understand the advantage of cutting and bending 3 tabs at the bottom of the chimney to put it on the flue gallery over the hole. Can’t you just make the hole of the gallery a little bit smaller (1cm?) so the chimney can be put on top without it falling through and without the need for the tabs? And rendering up to up with vcrete for 8 inches high or something?

    I would think the gallery hole always has to be a bit smaller than the chimney diameter so the pipe can’t fall through? So are the tabs just there to ‘anchor’ the pipe more in place because they will be covered with Vcrete, thus giving more stability?

    Maybe these drawings make it more clear what I mean:

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  • Kris S
    replied
    I also dropped my tape measure in one of the hollow colums of stacked blocks

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  • Kris S
    replied
    Poured the table top...

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    Last edited by Kris S; 03-22-2021, 12:53 AM.

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