(Photo Credits to Santiago Jose Lopez Luro)
I recently had the pleasure of visiting an artisanal brick factory in Argentina. I was leading a heater workshop in Mar Del Plata, a coastal city 5 hours south of Buenos Aires, in which we were using unfired clay bricks from this factory. As mortar we were using the exact same mix used to make the bricks and we had run out so a few of us took an early-morning excursion to get more. The brick makers were all Bolivian immigrants and worked as a cooperative enterprise, effectively renting the space and the kilns from the family that owns the factory and working as independent contractors. The extent to which they had organized themselves to work efficiently was amazing. I’ll let pictures tell most of the story with a few captions. (All photos can be enlarged simply by clicking on the photo)
It absolutely blew my mind to discover that several of the kilns in use are actually gigantic bell stoves! The vaulted kiln is fired from 4 arched fireplaces at ground level and the only exit from inside the vault to the chimney is also at floor level. The photo above shows that the “chimney” is the air gap between two walls at one end of the vault and that the exit flues are at floor level and are quite small. The discovery of a giant bell was especially gratifying and exciting as we were in the process of building a bell heater and the kilns are large-scale models of the basic principle.
Despite the fact that they were loading the fireplaces with green wood, many pieces 10 inches in diameter, the chimney belched primarily white vapor with very little smoke. During the loading of new wood a significant amount of smoke was generated. Some of the wood still had leaves on it!
The two arched entrances to the kiln were covered with bricks mudded together. They observed the bricks at 3 levels through openings in the door and they were deemed “cooked” when the bottom layer turned a translucent yellow color. We observed a kiln that had been in operation for 4 hours and the top layer of bricks were glowing red with the bottom bricks not yet glowing. The average firing time is 14 hours, and then they wait 2-3 days before entering to collect the bricks. I noted that nothing came out of the observation portals (no smoke, no vapor, and barely any heat)–an impressive display of the power of the draft in the chimney.
There were two amazing tools they had developed for efficient and less painful work: one was a cart for moving bricks that balances nicely to lessen the load. One person can move up to 100 bricks at a time.
The other was a mobile work table which had a water trough and a flat work surface. The brick makers would rinse their two-brick mold in the trough, grab mix from the wheelbarrow and sling it into the mold, scrape the top of the mold and release the bricks onto the drying pad which was simply tamped earth with a sprinkle of sawdust. The table and wheelbarrow combination allowed them to work fast and comfortable, bending only to release the bricks from the mold.
The molds themselves were impeccable creations lined with aluminum which allowed for a perfect release.
They calculated that each brick takes 600 g of firewood. They were using many different woods but they mentioned Eucalyptus, Elm, and Acacia. That means each firing is 20,000 kilos of wood! It would be interesting to gather many data points from different brick-making operations to get a sense for the energy that goes into a stove built from different types of fired bricks. Would be interesting to compare the energy in a red brick and a fire brick, also.
Out of 32,000 bricks in a firing they said they lose maybe 10-15 to breakage. In the photo below I’m standing in one of the kilns ready to be unloaded, the “chimney” is visible above my head.
A competent brick maker produces 2000 per day and they are paid per brick. Walking the endless rows of bricks we found calculations scribbled into the bricks as well as the name of the brickmaker in every batch.
The bricks dry for a couple days on the ground and 2 weeks in a pile before firing. The whole operation is covered by greenhouse plastic.
The mud is mixed in huge pools by a tractor and is 3 parts sandy soil,1 part black, clayey earth, and 1 part sawdust. This mix is obviously not the perfect ideal for a heater–my feeling was that it lacked a diversity of aggregate particle size and the presence of organic material and sawdust is not great for density. The measured density was around 1650 kg/m3. The group hosting the workshop was intent on using unfired material and experimenting with a local product, however, and I was sure it couldn’t be any worse than the cob mixes used to build rocket heaters. I’ll soon be sharing about my experience building this and two other single-skin bells with unfired bricks (all are based on Alex Chernov’s 2012 WildAcres design)
While the brickmakers are filling their wheelbarrows from one pool, the other is being mixed by a man driving a tractor around in circles, a few feet deep in the mud. Both soils come from the property on which the factory sits. The mixing takes 12 hours.
The below photo shows us in front of the pool with finished mix. They keep it full of water, using the same mix to create a little “dam” to hold the water. The workers load their wheelbarrows taking from the “dam” and as they go they move mix around to maintain it. This way the water slowly seeps into the mix and keeps it at a workable consistency.
They also used older kilns which were fired from below, the flames entering the baking chamber through slits in the floor of the kiln. These kilns had no top on them. The foreman told us the vaulted kilns took longer but produced higher quality bricks with far fewer failures. The open topped kilns had average yields around 60% compared with 99% for the vaulted kilns.
The foreman said that the same company uses machines to extrude bricks but they never come out as good as the hand-made ones.