SAN JUAN DEL SUR—After building 18 rural schools using tons of cement, iron rebar and wood-baked bricks, the Newton (MA)/San Juan del Sur Sister City Project decided to celebrate its 25th anniversary by building its second “Green Preschool,” this time in the village of San Antonio de Baston.
What’s wrong with those traditional building materials?
For one thing, they have huge carbon footprints. The process of manufacturing Portland cement—which involves high-temperature baking of limestone—accounts for as much as 8% of all greenhouse gases. The mining, smelting, processing, and shipping of iron is also extremely energy-intensive and polluting.
In both cases the energy in question is petroleum-based. Traditional Nicaraguan bricks are also bad for the atmosphere and aquifer; they’re typically baked by cutting large amounts of hardwood from hillsides and burning it in open pits with the bricks underneath.
So our alternative was to use local, sustainable materials that make a minimal impact on the environment: quarry stone (piedra cantera) from Diriamba for the foundation; clay and sand from local farms to make Compressed Earth Blocks. We framed the school in fast-growing hardwood, such as Madero Negro. We made window shutters of locally available bamboo (strong as steel, bamboo sequesters CO2 more quickly than any plant in the world); and used local flagstone for the floor.
The piedra cantera is essentially compressed volcanic ash or “tufa.” The only energy involved is cutting it into blocks and trucking it down to San Juan del Sur.
The Compressed Earth Blocks (CEB) are made using our Cinva Ram press, made for us (for free!) by Grace Davison of Cambridge, MA. It takes human sweat and a few honorable blisters to dig and sift local sand and clay, sift them, mix them with a little water, and put them in the press. The blocks have to cure for two weeks before being mounted with a cement-free home-made mortar and stucco’d with a “repello” made of clay, sand and lime.
The framing wood (brought to the site by ox carts) does need to be de-barked and painted with a mixture of an insecticide and diesel fuel (very little).
The bamboo is used both for the liftable windows and the “nailers” (battens for nailing the roof to).
The floor is made of local “piedra laja” or flagstone quarried nearby, and laid in using a non-cement mortar.
Our design in these first two Green Preschools comes from a local mason/carpenter, Modesto Garcia, who made an elegant hexagonal kitchen for his Mom. We liked it so much we have copied the design in two rural communities, Cebadilla last year, and San Antonio de Baston, which is being finished at the time of this writing (February 2012).
You can see a slideshow about the Cebadilla school at http://www.flickr.com/photos/gringopinolero/sets/72157626590573808/ and about the San Antonio school at http://www.flickr.com/photos/gringopinolero/sets/72157629082373531/
To read more about the collaborations between the people of San Juan del Sur and those of Newton, MA, visit www.newtonsanjuan.org. For more detail about the building processes, write me at firstname.lastname@example.org.