What is Cast Earth?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 10 June 2019
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Cast earth is a building material made with a slurry of earth and plaster of Paris that people quickly pour into forms to make walls. This building technique is especially suitable for climates like that found in the American Southwest, where the weather can fluctuate radically between hot and cold. Earth walls provide excellent insulation, keeping structures cool in the heat and warm in the cold. The cast earth will resist freezing, rain, and heat to keep the structure weather-tight.

To make cast earth structures, people start by building forms. Walls can be straight or curved, providing flexibility in terms of the shape of a structure while retaining structural stability. No reinforcement is necessary for the finished walls, but it may be necessary to support the forms to hold the walls in place while they set. The builder makes a mixture of earth and plaster of Paris, and pours it as quickly as possible.

One challenge with this building material is the very rapid setting time. It is sometimes necessary to add compounds to slow this process. Once people finish pouring the walls, the rapid setting is a benefit, as the walls will quickly firm up and become stable enough for finishing. This method is much easier and more cost effective than rammed earth, adobe, and similar building techniques, and people can alter the finish on the walls radically to achieve a desired effect.


People can make cast earth with a variety of colors, and some structures may have stripes, swirling patterns, and other effects. It is also possible to use shapes inside the mold to create textured patterns on the walls. Windows and other openings can be built into the molds. Customizing a cast earth structure is very easy during the planning process, as people can easily change shapes, angles, and other characteristics while setting up the molds.

Like many new building processes, cast earth can be challenging for government agencies charged with setting and enforcing building codes. These agencies attempt to keep pace with new techniques but do not always succeed. People planning cast earth structures may want to meet with building inspectors and contractors to discuss the situation and determine what additional steps, if any, they need to take in order to make a structure acceptable under the building code. Building inspectors are often very willing to work with people who are pioneering new building techniques in the area.


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