Building with earth: adobe, mud bricks, compressed soil

The lack of shelter in developing countries is a constant problem. Mainstream materials and technologies are far from being a solution for the poorest sectors of society, which have to struggle for their daily bread. It is clear that a response to this situation must have a radically different political and technological approach. Self-construction with clay has proved to be a most appropriate response in several countries of Asia, Africa and Latin America and, perhaps, it is the only possible way by which poor people can get a decent house.

In some Asian countries, such as Tajikistan, clay is taken directly from the ground and molded in the foundations to build up walls which grow higher as the clay dries. However, this article concerns itself with adobes or “sun-dried clay bricks” and their correct and safe use for dwellings according to experiences in different parts of Latin America.

The process begins with a correct selection of the soil to make adobes, that is, a soil not of pure clay, but that contains sand as well, in an approximate range of 40 to 60%. The soil is mixed with water and left for three days to achieve the appropriate fermentation. Then, some test adobes are made. In most cases, natural fiber is added to the adobe to obtain better results. If adobes crack in the drying process, sand must be added, but, if they do not resist a man´s weight once they are dry, clay is the material to be added to make them stronger. In any event, a practical test must be carried out in order to obtain the right mixture.

Once the appropriate mixture is found, adobe production begins with the use of metal or wooden molds. Where seismic conditions exist, the molds should be square and a size of at least 30x30x8cm, often 40x40x8 cm is used. Half size adobes should be produced for easy fitting in corners and “T” wall intersections. Adobe bricks are dried in the sun and they can be used after 10-15 days, once they are totally dry.

The plot of land for an adobe house should be level, dry and solid, and the house must be placed on the highest part to avoid water penetration. Foundations must be strong, and 1.5 times the width of walls, for which cyclope concrete (calicanto) is recommended. The first layers of the upper part must be watertight in order to protect walls from erosion. To assure this, the foundation of cyclope concrete or bricks can extend above the surface. In area of high seismic activity, a concrete ring beam is obligatory.

The first row of adobes must be laid using a lime mortar and, afterwards, the same clay material as used for the adobes is used as mortar.

The shape of the house should be either square, rectangular or circular. Because of earthquakes, no irregular forms are recommended. During construction, all walls should be built up evenly, but never more than one meter a day, in order to protect the first layers from excess weight until the mortar has dried out. The total length of the wall should not be ten times greater than its thickness, otherwise, buttresses, also recommended for all wall intersections, would become necessary. Openings for walls and windows should not be wider than 1.20m and the sum of them should not be more than one third of the total length of the wall. . Openings may not be located closed to corners. A reinforced concrete beam should be placed on top of the wall, as a solid base for the roof construction. Often this beam may serve at the same time as lintel over doors and windows.

There are no specific rules for roofs, but the overhang must be as large as possible in order to protect the walls from the rain. Be aware that in earthquakes it is often a collapsing roof that causes the walls to fall, so make sure you build a solid structure !

Walls must be plastered for protection from rain and erosion. Experience has revealed that a first layer, with a sand/clay mortar at a 3:1 proportion is best. Its thickness should be just enough to have a flat surface. Then, a finishing coat with a lime mortar (lime:sand=2:1) is applied with a thickness not exceeding 2mm.

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Peter Arndt
Social worker and Mechanical technician
German, English, Spanish
Project administration and management, social organization, mechanical innovation


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