Soaping and Stoning

This post was written by Spring 2018 intern, Callie Ochsner.
Recent experiences call to mind the forces that are shaping our existence here, the build up and break down of ourselves and our surroundings.

The focus on the build sites this week was all around Tadelakt, the traditional Moroccan lime plaster that lines the showers in the houses built by Community Rebuilds. The plaster is built up in layers before being finished and burnished to a glossy sheen.

The process begins with limestone. This naturally occurring sedimentary rock is formed mostly of calcium carbonate, or calcite. When limestone is heated to temperatures near 2000 degrees Fahrenheit, it releases carbon dioxide and becomes calcium oxide. When water is added to the calcium oxide, it becomes calcium hydroxide, or hydrated lime. That hydrated lime is the binder used for lime plaster. When hydrated lime comes in contact with carbon dioxide, it transforms once again into calcium carbonate, effectively becoming limestone again.

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Finished tadelakt in one of the showers.

Being a lime plaster, Tadelakt depends on this lime cycle to be effective. The technique is dictated by the behavior of the plaster itself, meaning that moisture and timing are the essence of the process. Three thin layers of lime plaster are applied to the shower walls, the last one troweled on the surface. As the plaster hardens, metal trowels, plastic trowels, and finally polished stones are used at specific times to smooth and burnish the plaster, compressing particles together and creating an impermeable skin. Finally, olive oil soap is applied to further hydrate the surface as well as contribute stearic acid. This reacts with the plaster to create calcium stearate: soap scum that protects the surface.

One inspiring characteristic of lime plaster is its ability to heal itself. In any lime plaster system, there are free limes that are unreacted. When a crack forms in the surface, those free limes travel to the scene and, once exposed to the carbon dioxide, continue to form a limestone matrix in that space. The crack, though it may be visible from the outside, has actually been healed from within. The matrix is perpetually building itself.

To punctuate a week of assembling limestone, a trip to Druid Arch in Canyonlands National Park revealed masses of stone being broken down and eroded away. In this geological area, layers upon layers of sediment were deposited over hundreds of millions of years by many different water systems and climates, compressing and creating magnificent strata of colorful sandstones and limestones. Starting about 15 million years ago, geological uplift caused these layers to rise thousands of feet in elevation. Water began its work, rivers and streams eroded and transported sediment as freeze and thaw cycles cracked and weathered the exposed surfaces. Unique patterns of joints between sections of rock created weaker areas that disintegrated to reveal spires of rock.

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One of these spectacular structures is Druid Arch, a 450-foot-tall double arch comprising specifically Cedar Mesa sandstone, made up of ancient coastal dunes deposited over 200 million years ago. These dunes included red and white layers dictated by the iron content of each deposit. The trek to the arch was nothing short of magical. The trail wound through delicate ecosystems, living soil crusts, fractured and undulating rock layers, and paths carved by flowing water. The landscape challenged and impressed, making sure we understood how much we were at its mercy, how little power we possessed in the face of this perfect system. Our arrival at the arch came with awe and relief and a long rest. Though arduous, the pilgrimage was immensely rewarding.

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Right now I picture the binding of a sediment matrix, the curing of a lime plaster when I think about the group of people with whom I am sharing this experience. We begin as individual pieces of limestone, as separate grains of desert sand. With some heat, pressure, chemistry, and magic, what was once many separate parts becomes one system. Loose particles are brought into the matrix, pinholes and gaps are filled, and the system continues to grow and cure itself for as long as it lives. However, external forces are constantly wearing away material, transporting sediment from weak places and leaving the strong. I have a feeling that one of the most beautiful things we can hope for out of this is to let each other wear away and burnish our weaknesses, to be broken down and built up again, to be strong and impenetrable once we have found a way to exist together.


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