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Janine M. LeGrand 08-30-2009 08:03 AM

Hello from Uganda
Hi everyone,

My name is Janine and I am an American living in Masindi, Uganda which is fairly rural Africa. I have been enjoying reading many people's posts in this forum and want to try to build a basic wood-fired oven. The big challenge here is that most of the recomended materials are not available locally--no refractory cement, no firebrick, fancy tools etc. Here you may build an entire house using only tools such as a machete, a hoe, trowel and shovel. On the plus side, I am getting used to fixing things that break so that doesn't scare me and even a basicly workable oven would be a blessing--I have been without any sort of oven (not counting my dutch oven or my pan-on-pan homemade charcoal "oven") and I really miss breads and baking. Yesterday I was able to use a friend's propane oven and I baked french bread, sesame breadsticks, garlic herb foccacia and braided challa (spelling?). It was a great day off! Anyways, building an oven will be a real challenge but I would like to have an outdoor oven. I'm sure what I'll get won't be up to the standards of what I am hearing about, but I hope I can do something that will be able to get me some loaves of bread....

PS-- I considered making an adobe oven such as what I believe is called a "horno," but the latrine coverage in this country only around 60 percent so the soil is not exactly clean. Yes, locals build stoves out of mud and animal dung but dung is really not something I want (human or animal) near my food, even if the heat of the fire would sterilize any pathogens--the idea makes me lose my appetite. So I'm looking at cement even if it will crack or degrade quickly. Hoping for the best:)

dmun 08-30-2009 09:40 AM

Re: Hello from Uganda
Any sort of fired clay brick or terra cotta flat tile could be used to build an oven. Refractory mortar may be out of the question, but ovens have been successfully built with a mixture of clay and sand as mortar, and I'm sure that by the time it had been heated to baking temperatures a few times that any bacteria would be killed off. The thing with any clay oven is that it needs to be kept really dry, as the mortar doesn't become hard and waterproof. Your real problem may be a workable heat proof insulation. I'm sure that even vermiculite would be hard to come by in rural Africa. If you could get some sort of volcanic pumice that could be a workable substitute.

Keep us posted.

texassourdough 08-30-2009 09:57 AM

Re: Hello from Uganda
Welcome Janine!

One of the neat things about a WFO is it gets hot enough to destroy just about any hydrocarbon so sterility of the oven is not much of a concern. While I can understand your desire to not "cook" on potentially contaminated soil, dmun's suggestion of clay bricks/terra cotta tiles can easily provide you a "clean", nice floor to cook on and for lining the oven. What is beyond that is not so critical. For a dome an old barrel might work well. It would burn/rust out fairly soon but...ought to be cheap and easy to replace. While an oven without insulation will definitely lose heat faster, earth and cob ovens have been built for thousands of years all around the globe. I would not worry so much about heat loss for dry dirt is a fairly good insulator.

Good Luck!

Janine M. LeGrand 08-30-2009 10:24 AM

Re: Hello from Uganda
Hi Dmun,
Thanks for the quick reply. Yes, vermiculite and/or perlite are not available around here. The bricks I can get are from the mud down the hill, hand-formed (so every brick is a different size). These bricks are fired once using very primative methods--they are very soft. We usually cut these bricks using a machete. Volcanic pumice is an interesting idea but I have never seen anything like that available here. Do you think there is any way wood ash might be used? I thought I might have heard something about ash in an early Roman oven. I can get bags of cement and have made a foundation, circle of bricks enclosing a bottom wood storage area, and a concrete support slab but haven't started on the oven per se yet. When you recomend clay, do you mean clay soil? That I have, but not if you mean like sculptural clay.... If I build the oven out of these local bricks do you think clay and sand would be a better motar than cement with sand? Everyone warns not to make the ovens out of Portland cement, but what actually happens if you do? I don't care much about appearances and am willing to patch frequently if needed. I have heard of at least 1 individual report how he broke the rule and used portland cement and his oven is still working well many years later so apparently sometimes you can get away with it--not that I'm saying you should if you live where refractory cement is available. I was thinking of using wet sand to make a mold and putting cement on that to make a dome--then seeing if it would stay together through the heating process. Similarly maybe cement bricks (unmortared) on the cement slab to keep the fire off the slab and replace these bricks as often as needed. Cement bricks here are made so the bricks are the same size, unlike the mud bricks. Local bricks for an oven floor would be a very uneven surface plus what is in our soil here is not what I want touching my food...

On the insulation, yeah I think that will be a real problem. At least here wood is cheap--you can get a pickup truck's load of firewood for about $10 US. So maybe lots of fire and fairly quick cooking foods?

I appreciate your taking the time to try to help me with this crazy project! Thanks.


dmun 08-30-2009 10:39 AM

Re: Hello from Uganda
Wood ash is an idea, it's heat resistant, and fluffy. You'd have to keep it really dry, but with your cut-it-with-a-machete bricks you'd want to keep it really dry anyway. Under the floor it would compress too much to be useful, but over the dome you could treat it like loose vermiculite.

Is there any kind of light weight stone like Tufa that you could layer under the oven floor?

I think you're better with the local mud bricks than the portland cement based ones. And yes, clay soil is usually a mixture of clay and sand, which it what the mud-based mortars are anyway.

Janine M. LeGrand 08-30-2009 10:41 AM

Re: Hello from Uganda
Jay, thank you for your suggestions. The idea of dry dirt as an insulator is a great one--dirt I have!!! I also have a pile of sand so I was thinking of using that as a form. I know you're right about sterility, maybe I just have to get over my squeamishness. I would like to have a flat floor for the oven though. The cement bricks are made equal in size. The mud bricks vary a lot in size. Cutting mud bricks wouldn't seem like a good option as cracking them with a machete makes pretty rough cut and they often break where you weren't wanting them too.

Barrels are not that easy to find here. Never seen the wood kind and haven't found a metal barrel with a known safe history--still looking for a cooking oil barrel or such. I don't really want one that had unknown chemicals in it. I already have sand on hand and I like the idea of using it wet then digging it out so I can later use the sand in another project.

Thanks also for the quick reply and your helpfullness!

Janine M. LeGrand 08-30-2009 10:54 AM

Re: Hello from Uganda
I can't think of any lightweight stone found here. As for the bricks, actually when used with mortar of cement and sand they stand up to the rain well--that is the second most common material for building houses here (mud/reed is #1 due to cost). Those who can like to plaster on a coat of cement but many can't. Half of my chicken house is made of these bricks, unplastered, and shows no sign of water damage. For the oven, do you think a plastering over with cement would be good enough to keep the water off? Our weather is very mild here.

One strange thought .... some solar ovens use a trapped air space as an insulator. Is that something to consider? Or maybe build in a space and add in wood ash?

You've got me thinking:)

texassourdough 08-30-2009 11:34 AM

Re: Hello from Uganda
Hi Janine!

I thought about the barrel history and figured you MIGHT be able to get a clean one. I should have mentioned the contamination issue! The real concern in a barrel will be heavy metals. The organics will burn out. But...yes, a dirty barrel would be a much bigger concern than "infected" mud. The latter WILL be sterilized. One of the magical moments in using a WFO is watching the interior clear of soot and tar when it reaches 750 degrees. Always impresses!

Your mud bricks are sun dried are they not? You might be able to get/make harder bricks by baking them???? (I am pretty confident you can and wood ash is probably one route but I don't know brick chemistry...). The clay referred to is ordinary soil clay - nothing special (yes there are better and worser clays based on clay content but...). It is (as I understand it) the standard starting material for building earth/cob ovens. It can get pretty hard with baking.

Regular cement loses strength and structure very quickly when heated to WFO temperatures. As I understand it, the oven would basically disintegrate and you would end up with cement dust all over the inside of the oven. Regular Cement can stabilize the exterior but not the interior.

You might try an experiment of making baked bricks from clay and wood ash with and without sand. If you can make a moderately hard slab it might be able to serve as the floor. People often stress a bit about small gaps in the floor, but they fill in with ash and its no problem (obviously you don't want large gaps).

Good Luck!

Janine M. LeGrand 08-30-2009 12:00 PM

Re: Hello from Uganda
Jay, thanks for the tips. You're the first person to actually answer "what happens if you use Portland cement?" If anyone has first hand experience on this I would love to hear it. OK, now I'm leaning toward local brick for the walls with a cement outer coat plastered on. These bricks are first sundried then stacked up in big stacks with room for a fire inside the stack, then the fire is burned inside the stack of bricks.--they are not hard like US fired bricks! I'm guessing the motor between the bricks can be made from mud the same way mud/reed houses are made--lots of stomping in the mud. I'll have to consider more about the oven floor and I may try experimenting as you suggest. Do you think it would be helpful to put a layer of dry dirt on the concrete slab under the oven in order to insulate? Or, it would be easier to make it stable and level by puting down mud instead of dirt then let it dry. Would doing that help reduce heat loss from the oven to the slab and/or reduce heat damage to the slab? Or is it not worth the trouble? Anyone feel free to pitch in with an idea!

I hope to get the support slab in place tomorrow. It is built, but as I didn't have wood that I thought was strong enough to hold wet concrete up, it was built on the ground and now we need to raise it and put in on the brick wall of the firewood storage area. Then I can start working on the oven and/or insulation.

cynon767 08-30-2009 12:37 PM

Re: Hello from Uganda
Some of the earthen oven builders use empty glass bottles packed in straw/sand/clay under the floor as an insulator; it's not as good as some of the other high-tech stuff, but it does create airspace and insulates better than raw dirt. When packed into clay, straw actually insulates very well and does not burn out. I expect that the mud/reed mixture could actually be adapted to insulate relatively effectively.

If it were me, I'd use the local brick inside the oven, covered with a mud reed mix- heavy on the reeds to increase insulation- and plastered over to protect the mud.

You might try taking a look at Kiko Denzer's information- he has a good book about building low-tech earthen (clay or cob) ovens, with good info about insulation of the sort that will be available to you.

good luck lifting up the support slab... that sounds difficult. If it cracks while lifting, it might all be for naught. If that does happen, I'd seriously consider whether, since you don't have the sort of plywood you'd need to support the wet concrete, you'd be better off just building a solid stand (i.e., walling off the box and filling with dirt/rubble) and pouring the slab on that.

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