Plasters and Tiles: A Guide to Earthen Materials

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Interior of cob cottage in Austin, Texas.
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Interior of cob cottage in Austin, Texas.
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Interior of cob cottage in Austin, Texas.
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Interior of cob cottage in Austin, Texas.


Earth is one of the loveliest and most practical materials you can walk on, inside or out. Floors placed directly on the ground have access to the earth’s thermal mass, and help keep a house warm in winter and cool in summer. Earthen floors consist of layers of gravel, an optional moisture barrier, some straw for insulation, a layer of sandy soil for a subfloor, and layers of earthen floor mix–clay, sand, and water. Earthen Floors (The Canelo Project, 1999) is a great short primer on making an earthen floor, and it comes from Bill and Athena Steen, already famous for their straw bale building workshops.


Earthen plasters surface earthen materials to waterproof and weatherproof them. Made from clayey soil and water, plaster provides a finished look. Some cultures mix in sand, straw, plant fibers, and ox blood for color and manure for texture. But today you can buy plaster pigments to provide color without killing an ox, ground ­psyllium seed to provide the texture and to help hold the plaster together. Many adobes are finished with a traditional plaster of lime and water that turns the dark brown earth to bright white.

You can plaster over wood or brick, or synthetic countertop ­materials, almost anything that has enough texture for the layers of plaster to adhere to. Add earth to your home in places that can absorb the sun, and the heat will be slowly released long after the sun has left.


The ancient Egyptians were the first to make and use ceramic tiles around 4,000 b.c. Tiles are merely slabs of clay which, traditionally, were hand molded in boxes and fired. (Terra-cotta means “burnt earth.”) Today’s tile manufacturers–the majority are in Spain and Italy–often use dry clay. These ­factory-made tiles are amazingly flat and thin and it’s easy to be very precise with them; they are also waterproof and easy to clean. Some people prefer to use more expensive handmade tiles from craft-based workshops or antique salvaged tiles where years of use soften their pattern and appearance. Like earthen floors, tiles, especially old ones, remind us of Europe at the same time they conjure up the cultural traditions of North Africa, Mexico, and the American Southwest. Like all earthen materials, tiles act like mini-solar collectors. They take money and effort to use, but they last forever.

A Boyhood Memory

“When I was a boy, my father was the main one to look after the church. Once when we had been up to southern Colorado to visit part of our family for a couple of weeks, it had been raining here almost every day we were gone, heavy rains. The day after we got back, my father took me with him to go see how things were with the church.

We could see as soon as we walked up to the church how heavy the rains had been. The adobe plaster was washed away here and there, and the winds had blown a cottonwood limb onto the roof. When we went to open the doors, the wood was so swollen by the water that we could barely open them.

When we got them open and saw inside, we just stood there awhile not saying anything. There, growing out of the adobe floor, was a young stand of wheat.

I remember trying to convince my father to leave the wheat alone–it seemed right to me that it should be there–but he just smiled and said, ‘Mi hijo, you know we can’t worship the wheat.’ In a couple of days, everything was back to the way it was, but I never forgot that day.”

–Elder of northern New Mexico village, from The Persistence of Memory, New Mexico’s Churches (Museum of New Mexico Press, 1991).

Ask yourself, the realtor, and the county property records office: What about the earth under the house? Is it landfill? Was it once a toxic waste dump?

Consider the landscape. If you are knowingly building in a floodplain or an area prone to mudslides, you will have no right to be angry with Mother Nature when she takes your house.

Integrate your house design into the landscape if you are building, or look for houses that show consideration for topography if you are buying. Then your house will belong to the earth rather than stick out of it.

See what is growing on the lot for your new house. If it is a wheat field, consider whether you want to be part of the growing problem of sprawl in which productive farm and ranch land is turned into housing developments. If nothing grows on your lot but rocks, forfeit the idea of a garden or find a place with more productive soil.

Mother Earth Living
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