Hello from Uganda

[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.

[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



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

[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.

[texassourdough]

Re: Hello from Uganda

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

[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

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

[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

[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




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

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

[ThisOldGarageNJ]

Re: Hello from Uganda

Hi Janine,
I looked up Pozzolanic cement and found this:

The Pozzolanic cements are comprised of fly ash or volcanic ash and a chemical binder. This combination produces a very dense matrix that has a slight porosity, thereby dramatically reducing the material’s susceptibility to gas and liquid intrusion thereby making it a more durable repair material.

If this stuff is made with volcanic ash it might have some kind of heat resistance ? I guess you might have to do some more research, Google It... It has a lot of good qualities it may be what you need..
Mark

[cynon767]

Re: Hello from Uganda

The straw, being a hollow linear fibrous tube, is mostly air. That's what makes it both a good insulator and a strong building material; it turns a dense sticky material like clay or mud into a porous matrix of tiny tubes and interwoven fibers. It's the original high-tech composite material!

The fact that the individual lengths of straw are isolated from the outside air supposedly keeps them from burning out. The ones that char still provide insulation; even if they burned out completely they would still leave behind the airspaces in the clay which do the job of insulating.

I have not used the material myself, but have read that short (2-3 inch) chopped lengths of straw work best, mixed into a slightly sandy mix of clay/mud.

I'm glad to hear the lifting operation was successful!

[Janine M. LeGrand]

Re: Hello from Uganda

Hi Mark,
I appreciate the encouragement. The cement here is not a ready-mix. The bag is labled "Multipurpose Cement for General Application" and " Pozzolanic Cement US EAS 18-1:2001 CEM IV/B(P) 32,5 N" which is pretty much greek to me but I assume it is Portland cement. You have to mix with sand and/or gravel. A 50 kg bag runs about $15 US here in this town. I also have seen lime available locally though I haven't bought any yet.

I am about 3-4 hours north of Kampala (the capital) where you can get many more things but transport is an issue. I get around locally here by a small motorcycle, but to go to Kampala I take a public bus or, if I can, I get a ride with a friend. It isn't exactly easy to bring back heavy items. It is possible to hire a large truck, but I haven't done it and it is complicated and expensive. Complications include things like no street addresses here. Having things sent from the US is of course expensive (say $50 for an average size box and it takes 1-2 months for Priority (despite what they say in the US post offices.) I don't have valuable things mailed as there is a chance they won't arrive.

Its a bit of a challenge living here, but very interesting.

--Janine