It was wonderful to return to Sabana Grande for a second project this year. Last year I was able to teach the communities different possibilities of cob, wattle and daub, variations on taquezal and wattle and cob, bottle art and sculptural techniques, using adobes for benches, earthen floor, and how to make clay and lime plasters that will last and be beautiful. This time, after assessing the desired project, the site and location, and the financial resources, I decided that working primarily with adobe was a sound choice. It would allow the women to continue to work with the vernacular building style and make the bricks themselves. This would provide them with income for the 2 weeks of adobe brick making. Also, the field where the youth center would be is a bit if a cooker and the thick adobe walls would buffer the day time heat. The thermal mass of the adobe stabilizes the rather intense day time heat and keeps it cool until night time when the temperatures drop again and draw the heat back out of the bricks.
One of the challenges I have seen with adobe and ”modernizing” it with plasters is poor preparation, proper hydration of the substrate, and insufficient understanding of how plasters work well. The people in this region never used to plaster the adobe and then jumped right to cement stuccos, which has proven to fail over and over. But they like the idea of smoother surfaces that are less rustic and less likely to provide housing for insects. Since this is a youth center we chose to build circular to create a nice community meeting space, create some playful elements, and allow the curves in all directions to make for stronger plasters. On the other new adobe buildings there, most of the sharp 90 degree corners are already damaged and have lost their plaster. We are softening all the edges on this round building and using our best recipe of red clay soil, river sand, screened horse manure or burril, fresh cow manure, and guasimo. It makes for a super strong plaster that the kids can climb all over.
We began the project with leveling the site by hand. This is sun baked earth that was hard as rock. Hour after hour of pick ax and bar to break it up and carry it away in wheelbarrows. Then the continue digging for the meter deep by meter and half below grade foundation or cimiento. This took several dedicated people several days. Once the trench was dug it was time to build the stone and suelo cemento mortero foundation. The mortar is six parts clay based soil and one part cement. This allows for the foundation to absorb the tectonic uplift forces through it’s flexibility from the earthen element. The proportion of stone to mortar is about 50%-50%. We decided to continue the suelo cemento above grade for the stemwall or sobrecimiento. This isn’t recommended for it’s vulnerability and often straight concrete is used, but we had so much success last year in using earthen mortar and covering between the stones with a thin cement mortar that we decided to do this again and minimize the concrete use in the building.
Once we finished the foundation we were ready for the workshop to begin. We had one thousand adobes bricks, built to the standard for adobe mejorado, sized for seismic strength at 14x14x4 inches. Also several yards of river sand, several more yards of red clay based soil, and dozens of bags of burril and rice straw. We had sixteen courses of adobe to stack and two curvy cob walls to break up the interior space and continue outside to provide shade and places to play. Our walls were built to be in height, no more than 8x the width of the bricks. This provides a more stable wall system. We also introduced burlap strips in the mortar layer of the three middle courses (7-8-9) for additional tensile strength.
I will be returning in a few weeks to work on finish plasters, earthen floor, and a community art project as a sculptural mural on the outside wall. The folks there are putting on the tile roof, finishing the cob walls, and softening all the edges of the adobe for a more enduring plaster. Stay tuned!