Initial build ideas - thoughts?

[di11on]

Hi folks,

When people speak of a 28" or a 32" oven.... is that the width of the interior cooking space or the overall exterior width?

I'm considering building a semi-portable small oven with an overall exterior width of around 28" to 30". Is this possible? Will it work ok?

This is what I'm considering:

- A treated solid pine base (using 90x90mm wooden beams - similar to in this video: https://www.youtube.com/watch?v=i0foHjPVbP4)

- For bottom insulation I'm considering a layer of 45mm Rockwool with a 50mm layer of vermicrete on top.

- For the cooking surface and entrance tunnel/arch, 5x11x22mm refractory bricks

- For the dome I'm considering using a mainly cob (if I can find clay anywhere).

I'm considering a final layer to weather proof it and for aesthetics if possible... what should I use here and how thick should my cob layer be at a minimum?

Any thoughts or feedback?

[Greenman]

Re: Initial build ideas - thoughts?

Hi Di11on - The dimensions usually referred to are the internal diameter of the oven. You would end up with a quite small oven even if the material you used was quite thin and that creates problems with heat retention and durability, particularly if you want it to be portable.

I am not sure about rockwool under the vermicrete, it is likely to compress.

The cob I am not sure about how it will cope with being transported.

Most of the ovens that are made to be moved around are made of refractory cement of one kind or another. Suitably reinforced they seem to provide the strength, the ability to cope with the temperatures and end up lighter and thinner than brick domes.

I am sure that there are folk with experience with the various elements that you want to combine who will provide more feedback but the combination of materials you propose would be challenging and I suspect somewhat experimental.

Good luck with this, I hope it all comes together for you. I will follow with interest.

[di11on]

Re: Initial build ideas - thoughts?

Thanks for the reply.

I am wondering if the portability requirement is too limiting. I'm in rented accommodation (in the South of France). Rather than limit my options, perhaps I should just take the view that this is an experiment before I build a "proper" one whenever we buy?!

Is it possible to build the dome with just refractory cement? I am finding it so hard to find clay, that I am looking for alternatives. I guess you would add sand to the refractory cement - in what ratio? What do people generally use for the outer layer for weather proofing and aesthetics?

Edit: Assuming the rockwool under the Vermicrete is ok would 45mm (1.75") of Rockwool + 50cm (2") provide sufficient insulation under the oven floor?

Edit2: Funnily enough, I have had an email from a local artisan's supply store who have 25kgs of red powdered clay which they say is suitable, for €23 a bag. A 25kg bag of refractory cement is €13 here...

In the end of the day, my objective here is to use the materials that give me the best performance for a given weight and volume. With this in mind, what do people think would work best. Sounds like a refractory cement approach will give me a better performing oven than using clay for the same volume. If I use refractory cement, do I need an insulating layer?

[cobblerdave]

Re: Initial build ideas - thoughts?

G'day
I suppose it gets down to some real simple terms like portable and movable.
I helped a friend out a few yrs ago who moved house and his first oven, a cob became garden fill with the move.
His second oven was a pressed clay paver oven, built on a hard wood pallet.
It was a cracker of an oven. Easy to build as he did most of the work. I just sat and watched ( and drank his beer).
He finally got a job down south and the oven was loaded into a Trailer took 6 of use to load it. G
Unfortunately I lost contact and often wonder how it survive its 1700 km move and if it has now found a full permanent base and and entrance and chimney as first planned.
Yes it was insulated top and bottom. But had no entry
Regards dave

[di11on]

Re: Initial build ideas - thoughts?

Thanks Dave,

I think you're right on the money. I've come to the conclusion that "moveable" is the key... and by that I'm thinking as long as you can get a pair of forks under it and as long as it's in a location that a forklift can get to, then that's as good as I can hope for. Putting wheels on it, for example, will only allow me move it around in a flat area and that's not of much use at all compared to how much it will restrict the build.

Regarding the building of an igloo type oven, I'm still at a loss regarding the best material to use for the dome, if not using clay. Will a mix of refractory cement plus sand work? Will I need an insulation layer?

[di11on]

Re: Initial build ideas - thoughts?

Ok, so I've decided on a 22" interior diameter (which I know is small).

I've also decided to go with a home-brew castable and I intend to mold main dome in segments like here:

The basic idea is this...

- Homebrew castable segmented primary layer (thermal mass)
- Rock wool insulation layer
- Outer vermicrete layer (precise composition to be determined).

So here are some questions:
1. Does this sound generally ok?
2. How thick should my primary castable layer be?
3. My primary layer will have expansion joints (like you see here) - will I need to cover this with a layer of homebrew before I put the rockwool layer? If so, how thick?

[stonecutter]

Re: Initial build ideas - thoughts?

Ok, so I've decided on a 22" interior diameter (which I know is small).

I've also decided to go with a home-brew castable and I intend to mold main dome in segments like here:

The basic idea is this...

- Homebrew castable segmented primary layer (thermal mass)
- Rock wool insulation layer
- Outer vermicrete layer (precise composition to be determined).

So here are some questions:
1. Does this sound generally ok?
2. How thick should my primary castable layer be?
3. My primary layer will have expansion joints (like you see here) - will I need to cover this with a layer of homebrew before I put the rockwool layer? If so, how thick?

David uses some small ovens he could probably answer that first question. If it was me, I wouldn't go that small.

As far as how thick, I would think with an oven that small, you wouldn't need more than 2"-3". If you are using 1:1:1:3, then I suggest 3". I'll not restate my opinion on using that ratio as a castable. But consider reducing the portland and replace the subtracted amount with more clay and lime.

A layer of any kind of mortar will crack when applied over an expansion joint. Better to just layer your mineral wool over the dome, then proceed with your perlcrete or vermicrete.

[di11on]

Re: Initial build ideas - thoughts?

David uses some small ovens he could probably answer that first question. If it was me, I wouldn't go that small.

As far as how thick, I would think with an oven that small, you wouldn't need more than 2"-3". If you are using 1:1:1:3, then I suggest 3". I'll not restate my opinion on using that ratio as a castable. But consider reducing the portland and replace the subtracted amount with more clay and lime.

A layer of any kind of mortar will crack when applied over an expansion joint. Better to just later your mineral wool over the dome, then proceed with your perlcrete or vermicrete.

Thanks for that - appreciate the thoughts.

What mix would you recommend for a castable? I don't think I've come across your thoughts on this before and I appreciate all the input I can get!

[stonecutter]

Re: Initial build ideas - thoughts?

Thanks for that - appreciate the thoughts.

What mix would you recommend for a castable? I don't think I've come across your thoughts on this before and I appreciate all the input I can get!

I haven't done enough to recommend anything beyond what I had mentioned about reducing the Portland in the component ( homebrew) mix. But the fact that you are building a temporary oven gives you a lot more freedom, because you already don't expect a whole lot. If you were casting an oven with longevity in view, I would go with a proper castable, and not a Portland rich mix design like 1:1:1:3

[di11on]

Re: Initial build ideas - thoughts?

Look what I saw browsing the building materials section of my local DIY store:



I'd have snapped it up if I had somewhere permanent to put it! Not sure if the price includes all the mortar and additional materials you need to assemble it. It has all the supporting stonework though... which all has that lovely warm local sandy colour. The stonework is beautiful... no cavity blocks here... and for €399... hmmm

Interestingly, they all seem to go for this type of "Roman" oven around here, which seems to be based on a focus on bread making... the dome looks much lower on these - elliptical rather than parabolic.

Edit: Looks like someone gave up in the early stages of trying to put it together!!!

[stonecutter]

Re: Initial build ideas - thoughts?

That could just as easily be a temporary oven. Insulate it and stucco...done.

[di11on]

Re: Initial build ideas - thoughts?

Hmmm.... it could, couldn't it...

I might just take a trip back and see what it does and doesn't include

Edit: on a permanent install, would you seal those expansion joints with refractory cement, or would you leave them open... I think I've seen pictures where the whole things gets covered in a layer of something or other?!?

[stonecutter]

Re: Initial build ideas - thoughts?

I think that I answered that on another thread...maybe not. Anyway, you can parge the joints with mortar, but it will still crack. Parge the joints, wrap the dome with insulation, apply perlcrete or vermicrete, then stucco.

[di11on]

Re: Initial build ideas - thoughts?

Thanks sc, yes you did answer my query in relation to a segmented dome casting.

It looks like the oven has been exposed to direct sunlight for quite some time. It looks like there is some superficial flaking on the surface. Would this be an issue? I guess since it's designed to withstand over 1000 degrees F, it should be ok?

[stonecutter]

Re: Initial build ideas - thoughts?

That looks like something like the brick I used for my oven. Uv doesn't damage masonry like that, so it's probably just the way it was cast. It's your call.