Plasters and Tiles: A Guide to Earthen Materials

Natural materials for your home.

| September/October 1999

  • Interior of cob cottage in Austin, Texas.
  • Interior of cob cottage in Austin, Texas.
    Photo by Gail Borst, courtesy of Cob Cottage Company, Cottage Grove, Oregon
  • Interior of cob cottage in Austin, Texas.
  • 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.

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