Friday, January 1, 2010

Urban Justa Building Workshop in San Francisco

July 25th somehow I just barely found out about a Justa IAP stove building workshop in my own area - Sebastián Africano and Honduriano ace stove welder Marvin stumbled into my shop in Berkeley and spent one day making a sheet metal oven and two days assembling/teaching in a beautiful permaculture yard in the Sunset district. Though we have never met, Sebastián and I have practically known each other for years based on the number of contacts we have in common (ADESEA/TWP in Tegucigalpa, ClimateCare/JPMorgan, Aprovecho, AbientalPV in Brazil, etc.) and it was a great opportunity for me to get dirty with these two compadres from ENASA.

This was to be a jumbo Mercedes/Cadillac of stoves, combining aspects of several different models - a metal bread oven like the ADESEA/TWP metal stove design (EcoFogon), an extra large plancha, a metal clean out port and place for gas to swirl on the way to the 4" (10 cm) chimney, a 4.5" (11.5 cm) diameter brick tube Rocket combustion chamber, and of course mostly found materials. I had just this week been struggling with my own steel plancha experiments - too thin and they will warp badly in intense flame, too thick and and they cost too much money to buy (a .63 cm plancha may weight 25 lbs!) - and will try their design of 1/8" (.32 cm) thick, with 1" (2.5 cm) square tubing frame around the perimeter and a sacrificial plate right over the firebox. This is set into a bombproof poured concrete retainer so that it locates perfectly and the sides are sealed from unwanted air intrusion.

First the initial flight of bricks is laid out, taking into account the dimensions of fixed parts like the oven, plancha, and cleanout port (the concrete platform had been poured in two layers the day/night before). The can and 45 degree cut brick tube were secured on top with shaped brick pieces (we would be chiseling many of the bricks to fit) and then we built up the rest of the brick layers - lots of hands involved at once - keeping everything straight and level. A hollow cavity at the rear was bricked over and a chimney support structure was built on top, keeping all openings in the gas flow path equal in area to the fuel entrance one.

The hand sawn (with a tungsten carbide hacksaw blade) 45 degree bevel on the combustion chamber did not match perfectly so the elbow had to be supported well and mudded in, then the area around it could be filled with volcanic perlite for insulation - Sebastián and I vowed to develop an alternative to just this and wood ash for a cheap quality filler material. The next day a perimeter concrete slab was poured across the top for the plancha to seat into, thick enough so that it wouldn't crumble over time - the adjustable flap behind the combustion chamber either steers the hot gas down around the oven or lets it flow the full length of the plancha. We used the stove just after building it, monitoring the oven and chimney temperatures to check initial performance - it was still a little wet but it heated up great with minimal wood or attention. We discussed that if a cook is not thrilled by the stove the first day, within 3 days she will have warmed to the change and be happy with its operation and performance - and it can be helpful to stop by, cook, and provide encouragement during this time period. User modified stoves are always a possibility, can defeat the purposes and advantages of the stoves, so should be prevented by any combination of hooks and crooks.

This was a great communal build, with nice weather and a great crowd - and what a beautiful stove they'll have to cook on and demo for the neighborhood - stoves in urban areas like this help raise awareness for clean and fuel efficient stoves to be built south of our border. I don't know if this urban backyard Justa barbeque building party will take off in developed countries, but it is a great educational tool. And in contrast to many more technical stover events we actually cooked a multi course meal - fresh vegetables, a rice dish, and 2 batches of cookies - ¡Qué rico!

Here are some links to Justa building:
another from Aprovecho, in Spanish, a video about the Justa in Honduras, and a detailed Justa efficiency testing article


Evo said...

You mentioned you were trying to find a plancha - have you seen

kushi said...

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