Clay oven question.

[Iona]

Hello all! Been off forum for rather a long time, busy setting up a business and hardly being in, which is nice, but I shall endeavour to rectify that now that I'm no longer in the rat race...

First thing now that I'm back though, is a question on behalf of my Sister who is working in Liberia, helping to set up a refugee camp for people from Cote D'Ivoire. She's trying to set up a field baking project there, as a means to get people producing their own food, and to bring them together, but having problems at stage 1: The oven.

They're essentially building a clay cob of 1.5m across by 1m high, I've never gone that big, so wondering if size is an issue. When they dig the sand out it's collapsing, the material they're using is straight out of the ground so I'm not sure of the clay content, her description of it feeling 'quite clay-y' didn't help me much. She's wondering if it's safe to add a bit of cement, I've never tried...

Her other question was whether they could use chicken wire between sand and cement to create integrity. Any thoughts?

Essentially, I've only ever done this on a small scale for fun, any advice/tutorials on larger scale ovens or working with raw materials would be very much appreciated!

Cheers, Iona

 

[Reaps72]

Try looking at this may be of use http://www.fornobravo.com/pompeii_oven/pompeii_oven.html
I downloaded the pdf & intend to use for a home project!

 

[ged]

...She's wondering if it's safe to add a bit of cement, I've never tried...

I'm sure it's safe in the mix, but cement is a little bit hazardous to work with of course. You don't want to breath in a lot of dust, or get it on your skin a lot. But there are much worse things.

Her other question was whether they could use chicken wire between sand and cement to create integrity. Any thoughts?

I've seen that sort of thing work well. Whatver you do the concrete (for want of a better term) will probably crack and some sort of reinforcing will help a lot. Even though cement tends to protect steel reinforcing in concrete from corrosion, eventually the chicken wire will probably corrode to nothing (especially at cracks where hot water vapour etc. escapes) so best keep an eye on it. BRC fabric would last a lot longer but would be a lot harder to form and probably more difficult to get hold of. The main thing that would concern me about any slightly dodgy structure of that size would be having it collapse if someone was inside it, especially if it's hot.

 

[Toddy]

Two things come to mind.
We make a willow or hazel structure and build the clay through and over that to create the oven. I'd be surprised if chicken wire would work tbh.......it would need a lot to take the weight of the clay.

The other thing that occurs to me is that perhaps if they made old fashioned mud bricks, the ones with chopped straw or something similar in the mix, and dried those first, then build the oven from them, that it might have a better chance of survival.

There's a very good book available on building these ovens, I don't have a copy, but a friend does. I could borrow and have a read up ? there's also a lot of literature on the topic in experimental archaeology reports, again, might be worth a good read.

cheers,
Toddy

 

[ged]

... I'd be surprised if chicken wire would work tbh.......it would need a lot to take the weight of the clay.

Agreed it probably wouldn't be much good with clay, but with some sort of concrete it can be good enough that people build yachts with it. They call it 'ferrocement'.

http://en.wikipedia.org/wiki/Ferrocement

The main thing is not to reply on a single layer of chicken wire in the middle of the concrete section, where it isn't doing as much for the structure as it can and a single failure can be catastrophic for the structure. Several layers on the other hand, well soaked in concrete, can make for a very resilient construction:

http://www.homestead.org/MarkChenail/ChickenWireConcrete/ChickenWireandConcrete2.htm

 

[Iona]

Thank you! Toddy, When I was taught to do this (on a much smaller scale as a fun thing to do at camps/festies with children) The woman I was doing it with tipped the clay she was going to use out on a tarp with a bit of water and a load of hay and had everyone bare fod stomping it through their toes to mix it in! Similar to your bricks I guess, but without the brick making? And ged, I'll cut and paste the link into an email for her to have a look. Might be really good. The materials they can get hold of are limited, as is everything else, so suddenly I'm getting calls all over the place asking what you do if you haven't got ...... Funny!

 

[Toddy]

When we fire up a clay oven the basketry interior burns too, but as a charcoal, and it doesn't cause any cracking or weakening to the structure. I don't know how the metal will react Ged, or the cement. Kiln bricks are porous and thus allow expansion and contraction of the structure, I don't know how the cement will work around a wire armature.
It might do very well, but I'd trust mud and clay and willow over cement not to shatter with some velocity behind it :yikes:

That's really my only concern with it.

Iona that mixing you describes is exactly how to make the mud bricks It can be hard work, but very satisfying and sundried will be enough to make secure enough to build an oven from. The cooking fires will slowly fire the bricks the rest of the way I reckon.
I mean, it works here, in sodden wet UK, for heavens sake. I know we have to cover over the oven to stop the rain saturating it, and the frost/freeze cracking issues, but it's still very useable

cheers,
M

 

[Mesquite]

Are they mixing the clay with anything or using it 'neat'?

If they're not using anything in it then it might pay to mix something like horsehair or chopped straw to help reinforce the clay. Similar to the way you make clay bricks.

The other reason it could be collapsing is they're removing the sand too soon before the clap has dried out properly. Something that's 1.5 x 1mt will take a fair bit of drying out.