Occasionally we have volunteers come and stay in return for working on a project. Rebecca and David, siblings from Cape Town, contacted me and said they were interested in permaculture and eco-projects so I asked if they’d like to try their hands at a rocket stove. By the time they’d arrived, they’d fully researched the stoves and had some plans and ideas.
A rocket stove provides a hob and both intensifies the heat of small twigs, giving greater efficiency, as well as reducing the amount of smoke. They can range from a simple small stove made from a can to a more elaborate affair – for example the three hob affair we were asking for.
Deforestation is occurring at an alarming rate in the Casamance and across West Africa, with obvious detrimental impacts for wildlife (and tourism), desertification (the Sahara slowly creeps south) and meaning that locals need to walk further find fire wood or pay more to buy charcoal. I was dismayed last year to see a nearby huge red hard wood tree – the only one in its area, illegally cut down and made into charcoal. So, rocket stoves provide a cheap and easy solution that just use a small amount of small twigs or bits of wood. There’s an added advantage of being waist height like a western style stove – something Khady declared she’d like, but I wasn’t sure – the old traditional ways are tough to change as my lonely looking hardly used chopping board attests. She still chops onions etc into the palm of her hand.
Anyways…for those that are interested, here are some design notes and photos of the stoves construction. Many thanks to Rebecca and David Viljoen for both the notes and most of the photos.
- Plastic piping – the type used for toilet outflows (used as moulds)
- Termite soil bricks
- Termite soil cement
- Cob (dark clay, potash water, manure, straw, sand)
- Metal piping (chimney)
- Small metal grids (for the burning wood to sit on)
- Decide on the desired height of the stove, and the number of hobs (this will determine width).
- Create a foundation using the natural bricks and cement.
- Cut plastic piping at a 45 degree angle so it sits as an ‘L’ (length of the two pieces depend on the size of the stove).The piping will be used to make the mould of the fire chamber and heat channel up onto the pots.
- Use natural cement for the mould, followed by a thick layer (at least 6cm) of cob insulation. The cob insulation needs to encase the entire layer of cement mould, and so for the horizontal piece of piping it needs to be laid down first. However, it is important to remember that the cement needs to be the only material in direct contact with the plastic piping; the cob encases that cement mould.The plastic piping needs to be left in until the cement and cob have set (dried) enough to hold shape when the plastic piping is removed.
- While the piping is still in, you can begin to build up around the mould with bricks and cement.
- If you want three hobs, two of your hobs will share a heating chamber (one fire source) – thus be connected by a horizontal tunnel (this means one fire chamber is used to heat two hobs). It is necessary to attach a chimney to this system (see the plan).
- The horizontal tunnel that connects the primary ‘L’ shaped system of the first hob to the second hob is the next component. A second two pieces of plastic piping, cut to connect at a 45 degree angle, will be used for this horizontal tunnel and the second hob (see the plan).
- The space around the primary ‘L’ shaped system has been filled with bricks and cement, and so now the second horizontal piece of piping can be laid down (don’t forget to make sure the cob insulation gets laid down first). This piece of piping will connect to the primary vertical tunnel, and so the connection needs to be incorporated into the moulding and joining of this piece of piping (see the plan).
- The vertical piece of piping for the second hob follows the same procedure. Ideally, all the vertical moulds will sit at the same height, as these are the hobs, and the stove top needs to be level.
- As before, the space around the piping, mould and insulation can be filled with bricks and cement.
- The same procedure is carried out with the metal chimney, which unlike the plastic piping is not a mould but a permanent feature – it will remain. The chimney is attached to the second hob’s vertical tunnel (see diagram). Insulation is necessary (to avoid heat loss otherwise funneling up to the hobs), but cement moulding is not (see the plan).
- If this is a three hob stove, like ours, the third hob is a new system; simply repeat the process, so that the primary ‘L’ system of the first hob is mirrored on the other end of the stove. This hob does not use a chimney. As before, be prudent with insulation and fill space up with cement and brick as you go. Ideally, use the plastic piping from the first hob’s system as it will be dry enough by now to gently remove the piping.
- Once all the moulds have been completed and the space around them filled and built up, you can focus on the surface of the stove. Build up the stove until it is in line with the top of the mould/piping – this is the stove top. Ensure that the stove top (the surface area around the holes/hobs) is smooth and level.
- Once smooth and level, try to incorporate ‘Skirting’ around the hobs. That is, build the stove top up by a few centimeters, so that the pots and pans will sit lower than the stove’s surface (see diagram). This is for efficient heating. Cement is best used to build up the stove top up.
- As the respective moulds dry, gently remove the pieces of piping.
- Turning attention to the heat chambers (the two horizontal tunnels where the fuel will sit and burn – it is important that the wood sits above the floor of the horizontal tunnel. We found a barbecue grid and cut it to size. When cut to size, the barbecue grid (reinforced by welding) sat elevated. The wood is then placed and burnt on this grid. To secure the grid, create grooves on either side of the tunnel, while the cement mould is still malleable. By doing so, the grid can be slid in.
We have cooked on the stove – it was indeed rocket like with flames jetting up through the hob. There are some teething issues with smoke, but this seems a common problem that we should fix.
Whilst they were here two of their friends – Manya and Hannah, also from Cape Town, were in the region and wanted to stay. They were keen to do something too and so built a keyhole garden. This is an African idea, originating in Lesotho I believe, where you make a small circular pile of compost with a “keyhole” shaped hole to walk into and access the centre. Kitchen waste etc is put in the middle and watered every day. This composts down and seeps into the surrounding circle of soil/compost, where you can grow salad, herbs and so on. The whole structure is traditionally held together with rocks – we made a palm fence as there are no rocks here – and situated near the kitchen for easy access. Given the difficulties we’ve encountered with growing veg and herbs, due to squirrels, chickens and so on, I was keen to make this well protected with a mosquito net protective covering.
We’re still building up the layers of compost, but it’s coming on strong.
Finally – as usual for me, there was a big coincidence in store. When I posted a photo on our instagram feed one of my old friends from Cape Town, Kelly, contacted me to say she knew Manya. And this is the second friend of Kelly’s I’ve bumped into in the past 12 months.