Hello from Uganda

[Janine M. LeGrand]

Re: Hello from Uganda

Hi Jamie,
Thanks for the explaination on why straw works as an insulator and the details on the desired mix. I think I will put down a layer of straw/clay under the oven. Also over the bricks of the dome of course. For under the oven, I could 1.) keep the straw/clay mix to the interior of the brick circle or I could 2.) extend the straw/clay under the wall bricks of the dome. Option 1 would not provide as much insulation as heat in the wall bricks would move down into the slab. However, option 2 might have a concern about settling. With option 2, the weight of the dome would be on the straw/clay and if the straw in the clay rots out or burns then I wonder about the structural strength of the clay with all the airspace. I wouldn't want to build the dome then have a section of it drop down one or two inches if the straw/clay collapsed. I am leaning towards option 1 keeping the straw/clay inside the oven circle for the floor build with the wall bricks resting directly on the concrete support slab. What do you think would be the better plan? Or, do you have a different suggestion?

--Janine

[Janine M. LeGrand]

Re: Hello from Uganda

I think I figured out how to show you pictures of the stand so far so you can see what I have done so far. The stand is a bit rough but should be functional. We ended up building putting up the circular brick wall at night by flashlight which probably wasn't the best idea but I think it will work. The concrete support slab was made first sitting on a bunch of grass on the foundation--the foundation was a good flat area so I used that. I built in wire handles in the support slab to help in moving it. After the slab was a bit cured it was dragged off the foundation so we could put up the wall around the firewood storage area. Then 10 strong guys lifted it onto the wall. The handles on the support slab will be covered in the oven build.
---Janine



Added comment: Oops, the photos aren't showing here on my computer. The next post has the photos--took me a little bit to figure out how to post them.

[Janine M. LeGrand]

Re: Hello from Uganda




OK, second try at the pictures--think this should work.
--Janine

[Rodneyf]

Re: Hello from Uganda

This build is going to be one for the books so please keep the pics coming and there will be a lot of us keeping watch.

[Janine M. LeGrand]

Re: Hello from Uganda

Hi Rodneyf,
I tried to get pics of all the guys moving the slab, but unfortunately some of them didn't want me to take photos. Here people can be sensitive about having their photos taken so no photos of that. It was pretty amazing--that slab was HEAVY and they took care of the job in a few minutes. I'll plan to keep adding photos.

Thought you might like to see the kind of bricks I am working with. They vary a fair bit in size and break pretty easily but are the standard building material around here. The way to cut them is to use a machete.

--Janine

[texassourdough]

Re: Hello from Uganda

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]

Re: Hello from Uganda

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]

Re: Hello from Uganda

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

[cynon767]

Re: Hello from Uganda

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]

Re: Hello from Uganda



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]

Re: Hello from Uganda

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]

Re: Hello from Uganda

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]

Re: Hello from Uganda

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]

Re: Hello from Uganda

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]

Re: Hello from Uganda

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