28" homebrew cast oven in walled enclosure Belgium

[Kris S]

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!

[Ronstarch]

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

[Kris S]

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?)

[Kris S]

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.

[Kris S]

I've got some other smaller bricks 5cm thick that I would like to make a nice arch with for the wood storage area under the hearth.
I went ahead and tried to arrange them free hand in a kind of low arch, Do you think this could work and not collapse? The more I look at it, the more it looks unstable?

I would like to use a 'flattened arch' instead of a true semi circular arch.

any advice on this?
is this doable without having to cut and taper (some or all of) the bricks?

edit: the internal widt of the arch in this case is 68cm and the heigth 27 cm.

[Kris S]

Here's an exmple of what I don't want: a semi circular arch:



And this is more or less what I would like: a flatter arch.
Maybe I should also try to taper the first 2 'corner' bricks as they did here?

[david s]

The flatter the arch the greater the sideways thrust and the problem is exacerbated by a heavier load on the arch from the top.The semicircular arch is not bad, but with the sides un-supported by buttressing still has quite a lot of sideways thrust. The pointed gothic arches developed to reduce the sideways thrust experienced with the semicircular arch. The only arch that can stand up with no, or failed, mortar joints is the catenary arch, as long as its base is not wider than its height. In the end you do what you can get away with.

[deejayoh]

I think what you want is called a "Segmental Arch". It's the design that's in the original FB plans. They're nice because they give more headroom for pans and such, but they're not as strong as a true arch.

the arch in the pic you shared looks like it could have some problems over time, due to side thrust.

[Kris S]

Well the sides would be butressed as the arch is meant to sit under the hearth inside the opening where I would store some wood. It's not for the free standing decorative oven opening arch

Maybe I can put some support under the arch in place as well, it wouldn't be very visible.

[sergetania]

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.

Honestly, at the oven cooking temps (350-500C) I can't tell a difference between different woods. It all burns so hot you don't even get much smoke. I really like oak because it gets the oven hot faster.

The build is looking great!

[Kris S]

This is where I'm at right now: the oven floor and perlite/vermicrete insulation layer are covered for rain and wind while I'm waiting for the fireclay to arrive, it should arrive tomorrow, but I won't be casting untill next weekend because I will be picking up some free slates and roof tiles for the roof. I'll get them both so I can see what I will like most.

I've also 'test stacked' the arch below and I think it looks great, but I'm not going to finish it yet, I first want to see how it looks like having two arches above each other, when the oven and decorative arch are in place, maybe I won't like it after all.

[Kris S]

Hi guys, looking for some confirmation that I’m doing things right before I start casting…

Here’s the oven opening mould, I drew a line and indicated ‘sand’ and ‘cast’ on it, this would result in this cross sectional view.
My reasoning for the ‘sand/cast line’ is that if I would put sand right up into the corner where the OSB-board and Alluminum sheet meet I would end up with a sharp and fragile edge as is drawn below.

Is my reasoning correct and can I go ahead like this?

[Kris S]

Also made a quarter arch to assist shaping the sand dome, I drilled a little 'depression' in the arc so it would pivot easier on the screwhead.

[david s]

All good so far. Creating the sand hemisphere is actually easier than you’d think. Eyeballing the profile and tapping the surface with the flat of a Bricklayers trowel produces a perfect hemisphere. The central stick to determine the height of the dome is better if it’s lightweight so it doesn’t, become a problem to remove from the casting. You can also stack some polystyrene boxes in the middle of the sandcastle to save on the amount of sand required. They are really easy to break up when you need to remove them. After casting the dome you will need to cut another mould plate, slightly larger than the oven mouth plate, to form the rebate at the oven mouth which will accomodate the oven door.

[Kris S]

Thanks David, much appreciate your feedback!

Yes, I might have to shorten the central stick a bit and put it on top of something to prevent it being stuck inside.