How to build a Rocket stove - a step by step guide

One of the problems that I've already mentioned about the solar cooker is shared by the Rocket stove, namely that the beneficiary families cannot be involved in its construction and therefore there is a risk that they will neither use nor maintain the cookers. On top of that there are a couple of possible improvements that would be interesting to try out - namely having separate and sloping fuel and air entrances to try and prevent people from choking the stove with too much fuel and hot ash and coals. The idea is that the fuel entrance slopes downwards to reduce the need for near-constant attention while cooking as the wood will "self-meter", falling down the chute as it burns at the tips of the sticks. Another benefit is that the stove can be used with charcoal, unlike the standard Rocket stove. The addition of a separate, upwards-sloping entrance for air should guarantee that sufficient oxygen enters the combustion chamber, while also helping to automatically empty the stove of ash as the fuel is burnt - thats the theory anyway!

The new design is the brainchild of Jerry, a technical genius who works for the CRC in Suchitoto. Some of his other ongoing projects include plans to install a micro-hydro plant to provide power for a community hospital and school with REDES, solar powered water pumps, biogas digestors and endless improvements for the Rocket stove - including an interesting idea for a hybrid Rocket, lit with biogas to help heat it up and burn damp wood as well as replacing the gas cookers that are often used for quick meals or hot drinks. Another idea of his is for a Rocket with two or three burners to accomodate multiple pots, or a large comal for cooking tortillas for extended families - there's lots of potential for REDES to adapt the designs to suit different families.

Yesterday Steph and I caught a bus up to Suchitoto to experiment with these ideas for the new design (and on the way she was serenaded by three teenage lads who happened to be carrying a guitar and ukulele with them!) We were somewhat lacking in the resources you might have in the UK for prototyping, so had to make do with recycling an old polystyrene board (ironically showing information about a CRC project building "Armenia" stoves which are mostly disused now) and some AIDS awareness posters, along with a cardboard box scavenged from the local shop for a mold. The idea was to stiffen the box with the polystyrene sheeting, which also serves to separate the wet adobe from the thin cardboard walls with the plasticised posters theoretically stopping water from seeping out...Jerry rather optimistically hopes to reuse this mold time and again for future stoves! The combustion chamber and various inlets for fuel and air are formed from empty drinks bottles filled with paper or water for stiffening and later removed once the cooker has dried.

The stove is primarily constructed from adobe, which requires clay-rich mud, so we were armed with a spade and pickaxe and sent off into the garden with a dustpan-sized sieve to produce a bucketload of fine-grained mud. Trust me, its a lot harder than it sounds as the clay makes the soil stick together in lumps and roll up into hard little balls that don't fit through our toy sieve. An hour or so later (and having provided a tasty feast for a swarm of mosquitos that suddenly appeared out of nowhere) we finally had enough mud to go with the sawdust that Jerry had been hoarding for months to make our adobe mix. The sawdust is a vital, if surprising, ingredient - ideally the finished stove would be fired to burn out all of the sawdust (any fine-grained organic material can be used) leaving a porous material not dissimilar to pumice. The trapped pockets of air provide the insulation vital for an efficient stove by reducing its effective thermal mass (the heat is confined in the combustion chamber rather than heating the whole body of the stove as happens in many designs of "improved" adobe stoves.)

After creating a dry mix of approximately 50:50 mud to sawdust we got to work on the remaining mud, adding water to make quite a moist adobe mix which was daubed around the base and up the sides of the mold to give a smooth surface finish about half a centimetre thick. This was then filled in with the mud/sawdust mix which was made up slightly wetter to ensure that it flows properly around the mold. At this point we ran out of both sawdust and time, so we agreed to return on Friday and rushed off to catch a bus back to San Salvador for our meeting with Seb and Edwin (who carried out the structural analysis of REDES' bahareque house) but thats a story for another time! [To be continued....]

As you've probably noticed Friday's come and gone now, and we now have a cardboard box of mud waiting for us in Suchitoto, slowly drying in the sun. The second day's work on the stove was a little frustrating - endlessly forcing mud through our mangled sieve until we had blistered fingers and decided that we must have enough to finish the stove, only for all of our adobe mix to be swallowed up by the mold without making a noticeable impact! We eventually filled it to a level where we could add the fuel and air chutes - old plastic bottles cut down to size and stuffed with newspaper, then balanced a square of polystyrene on top of the upside-down 2L bottle that forms the combustion chamber to try and stop sticks from sliding straight through and out the air inlet. Over the course of the afternoon we finally managed to fill the whole mould and ended up with a three centimetre cover of adobe at the top, which was a little less than we wanted, but once again we'd run out of time and mud. The mold was then covered in plastic to keep the water off it and left outside to dry in the sun.

Next week we'll return to finish the stove - the mold will be inverted so that our combustion chamber points upwards and hopefully we'll then be able to peel away the cardboard, paper and polystyrene layers of the mold to reveal a perfectly formed, dry adobe cooker! At least thats the idea.... [To be continued....]