Hello from Uganda Introductions Discuss Hello from Uganda in the Good Background Information forums; I am a bit (like a lot) beyond my experience here, but I certainly agree that straw under the dome ...

[texassourdough]

I am a bit (like a lot) beyond my experience here, but I certainly agree that straw under the dome walls will have loading issues with the potential for collapsing.

When you say put down a layer of straw/clay under the oven I think it needs a pretty good blend of straw and clay. The hearth layer won't be terribly heavy so it can probably have a fair amount of straw, I think I would mix it pretty wet so everything is well adhered. I like the idea of having some insulation under the walls. Perhaps you could still include straw but at a lower rate so it has more clay for strength. You could probably also include some brick debris to provide extra strength without adding as much conductivity as rock would???

This is a very interesting project! Good Luck!
Jay

[dmun]

I think the compressive strength of the straw/clay mixture is not much of a problem. Insulating firebricks are made with sawdust where the wood is burned out, and they have great compressive strength.

[texassourdough]

Good point, dmun! Maybe sawdust would be good to blend into the clay/straw???

[cynon767]

I tend to agree with dmun... the small insulating pockets of air formed by the straw, whether intact or burnt out, would be in the middle of hardened clay. Even though it won't be heated to the same kind of temps we often think of for bricks, it would still be fired simply by using the oven... it would probably be almost as strong as the rest of the clay bricks you'd be using, and would very likely have quite good compressive strength.

[Janine M. LeGrand]

As you can see, I am going with the suggestion of "straw" cut into short pieces. We sometimes are using a cleaver and sometimes scissors to cut the straw; it is a bit of work but goes faster than you would think. The "straw" is left over stems from the grass my goats eat, dried a little. We are using the support slab for a table as we cut. Next step will be to make the straw+sand+clay mixture and slather it on the support slab. Given the suggestions here, I'll put down a layer of straw+sand+clay all across the slab, then the floor brick then the walls of the oven using sand as a mold.
I'll put the entrance arch in place (already shaped on the ground) and a coating of straw+sand+clay. That's the plan and we'll see what happens.

--Janine

[Janine M. LeGrand]

Working on the oven--lots of work. I decided on using termite mound soil as my clay. Local building knowledge picks it as a very good building material and a scientific paper indicates it has a refractoriness of 1400 deg C. (Refractory Properties of Termite Hills under Varied Proportions of Additives, by Mohammed B. NDALIMAN available at Refractory Properties of Termite Hills under Varied Proportions of Additives from Leonardo Electronic Journal of Practices and Technologies). So we collected termite hill soil:

Here is a close-up of the soil:

We broke up the soil, added water, lots of short pieces of grass stems, and some sand to make an adobe:

Then put this on the support slab about three inches thick to act as insulation under the oven floor.
Then the local bricks went on top as the oven floor --though I have one more step I'll do for the floor next...

Next post you'll get to see the finished floor--I'm limited to 5 pictures per post which I'm sure is a good idea to keep the access time for people reasonable
Hope you're enjoying these pics!

[Janine M. LeGrand]

After putting down the bricks for the floor, since the bricks are very rough and uneven I decided to put down a layer of clay to even out the floor. I mixed termite soil with sand (higher proportion than for the adobe since I was trying to minimize shrinkage/cracking) and we smoothed this on. Actually, when the first layer dried it had a bit more cracking than I wanted so we put on a second thin layer. Anyways here is what the floor looked like when we finished:


Since then, as it dries we are getting small cracks again. I may coat it again, but I think actually even with them it would be OK as they won't interfere with smooth pizza movement or such, plus likely will just fill in with a little ash anyways.

Next step will be building the dome.

[texassourdough]

Way to go Janine!

Termite soil looks like a great choice. I also like the idea of a mainly clay floor. It will be soft at first but with time should become hard as a...brick. I suspect you will have to patch numerous cracks during the drying (for clay is pretty expansible on wetting) (shinking on drying) but the patches should be pretty easy and the end result should be smooth and hard.

Way to go! Look forward to more tales of Janine's oven!
Jay

[Archena]

Hi!

<Resists urge to explain what's in termite earth >

Looks great thus far! Did you decide for brick or adobe (cob) for the dome?
By the way, you can probably upload pics faster in the Gallery (I like them in the thread myself but the gallery is less limiting, I think).

I have a young friend who's heading for Uganda for a mission trip. It's one of the few African nations I'm actually tempted to visit (understand, I'm an extreme homebody who never even visited Mexico when I lived in New Mexico). Anyway, I'm enjoying watching your progress. Congrats!

[Janine M. LeGrand]

Thinking about what's in Termite soil--termite dung??? Given the soil here maybe some human and other critter's nasty's too. Actually, it is the human pathogens that give me the willies--I'm here as a health advisor/coordinator for the Church of Uganda and I'm all too aware of contamination issues. I can't think of any termite-human zoonosis so that part is pretty safe. I'll just keep repeating to myself "It's sterilized, it's sterilized, the heat of a WFO sterilizes it--besides it's stuck in the clay" Plus there's always the pizza pans--believe it or not I bought some in Kampala!

Cob or brick--good question. The deciding factor for me is do I have enough bricks on hand; I usually buy them by the truckload as I don't want to waste the transport cost. I think I have enough on hand for the oven if I use the half-bricks (broken bricks). So the plan will be to start with whole bricks and as I go up the dome and the circumference gets smaller I'll start using half-bricks. I'll use the termite soil with sand added as mortar. I think pieces of the brick are a little less likely to flake off as could happen with the mud given the surface cracking... Any flakes on the floor will get brushed off with the ashes, but don't want something dropping in my food. Hopefully after I've fired the oven that won't be a problem though. After the bricks, then I'll cover with termite soil-grass-sand adobe for insulating the dome. Lastly a coat of cement to waterproof.

Do you know if I should get some lime to add to the cement? Last time I checked it was available. Does lime make cement more waterproof?

Archena, glad to here your friend is coming to Uganda--many people know almost nothing about this country. Check with him and see if he is coming near Masindi. Masindi is near a popular safari area called Murcheson Falls on the Nile River. You can see crocodiles, elephants, giraffes, lots of birds, baboons, etc. there. I know a group of Americans mostly from S. Carolina are coming in December with Palmetto Medical Initiative (a great group of people--you can check out palmettomedical.org if you're interested).

Oh, on puting up the pictures--I put some in the gallery at first, but I couldn't figure out how to get the link to them in the thread post. At least this way works for me, putting them in the post.

Thanks for all the advice and encouragement.

P.S. I love the the Jim Elliot quote

---Janine