[Stoves] A heat-resistant insulation mix

[Xavier Brandao]

Stovers,

 

I wanted to submit another question related to the institutional rocket
stoves (IRS).

We encountered a problem with the insulation mix we used. In Benin, there
are only a few oven to produce ceramics. They are already used for bricks
and NANSU (kind of Jiko) ceramics. Demand for NANSU ceramics is huge from
metal craftmen. So big that one of them grew tired to wait, and made his own
ceramics, with a simple wood fire. It is of poor quality, and it breaks
easily. Since this option and building our own oven was not possible (too
expensive and we are not ceramists), we needed to find an insulation which
didn't need to be cooked. That is also why we want a metal domestic charcoal
stove.

So we followed a recipee described in the IRS manual. Between the inox
combustion chamber and the sheet metal outer body of the stove, we used a
mix of 6 parts wood saw dust and 1 part of clay. On the stoves we made in
the military camp (where they prepare from dawn till dusk), the mix almost
completely burnt after a few weeks of use, leaving only a thin powder at the
bottom of the space between the inox and sheet metal layer.

 

We don't have anything to analyse it, but we are pretty sure the powder pile
at the bottom is clay powder, the same clay powder we put in the mix. The
sawdust burnt because of the heat. Small smoke was coming out of the small
holes in the outer layer of the stove when in operation, certainly because
the sawdust was burning. We thought that was the plan : the sawdust would
burn and leave holes in the mix, making a kind of insulative ceramic. The
strange thing is that it didn't burn like that in the two first stoves we
made. At least not that we know.

Maybe is it because we then used water to mix the sawdust to the clay? The
mix clay-sawdust for the camp stoves was dry.

Or perhaps with such a thin layer of inox (1mm), the sawdust is meant to
burn completely, and 6 parts is too much for 1 part of clay. At one point or
another, the only thing left would be a pile of clay.

 

We are thinking about different things. We need to do without ceramics.

For the next stoves we'd like to replace inox layer + insulative mix by
bricks. It will be less expensive. We want to try to cut standard size clay
bricks to the size of our combustion chamber (it seems bold) and put them in
the sheet metal box. Then to bind them with something strong. And perhaps
had an extra layer of cement + clay, I think this is what you recommended
Crispin, to prevent users from breaking the bricks when pushing the wood. We
need something heat and shock resistant, long-lasting, efficient and cheap,
and that seems like the best solution.

 

As for the stoves left empty, it seems that the cooks don't complain.
Somehow, they are still efficient and clean. Air is also in insulator. But
we need to refill them. We think to avoid using sawdust, and put a mix of
clay + cement + water.

Do you think that would resist heat and last? What are your experiences of
making insulative layer, without the help of ceramics? And with cheap and
wide-spread material? Rock-wool for example is too expensive and too rare.
People here advise us to use laterite. It is cheap and to be found
everywhere, heat and shock resistant. Metal workers use laterite bricks for
furnaces. But I doubt about the energy efficiency, compared to clay.

 

Thanks in advance,

 

Xavier

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