Adobe

For the software company, see Adobe Systems.

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Renewal of the surface coating of an adobe wall in Chamisal, New Mexico

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Detail of adobe kilns in Arizona

Adobe (Arabic: الطوبى) is a natural building material made from sand, clay, water, and some kind of fibrous or organic material (sticks, straw, and/or manure), which is shaped into bricks using frames and dried in the sun. It is similar to cob and mudbrick. Adobe structures are extremely durable and account for some of the oldest existing buildings in the world. In hot climates, compared to wooden buildings, adobe buildings offer significant advantages due to their greater thermal mass, but they are known to be particularly susceptible to earthquake damage.

Buildings made of sun-dried earth are common in the West Asia, North Africa, West Africa, South America, southwestern North America, and in Spain (usually in the Mudéjar style). Adobe had been in use by indigenous peoples of the Americas in the Southwestern United States, Mesoamerica, and the Andean region of South America for several thousand years, although often substantial amounts of stone are used in the walls of Pueblo buildings. (Also, the Pueblo people built their adobe structures with handfuls or basketfuls of adobe, until the Spanish introduced them to the making of bricks.) Adobe brickmaking was used in Spain already in the Late Bronze Age and Iron Age, from the eighth century B.C. on. Its wide use can be attributed to its simplicity of design and make, and the cheapness thereby in creating it.

A distinction is sometimes made between the smaller adobes, which are about the size of ordinary baked bricks, and the larger adobines, some of which may be one to two yards (2 m) long.

Etymology

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Church at San Pedro de Atacama, Chile.

The word adobe (pronounced /əˈdoʊbiː/) has come to us over some 4000 years with little change in either pronunciation or meaning: the word can be traced from the Middle Egyptian (c. 2000 BC) word dj-b-t "mud [i.e., sun-dried] brick." As Middle Egyptian evolved into Late Egyptian, Demotic, and finally Coptic (c. 600 BC), dj-b-t became tobe "[mud] brick." This evolved into Arabic al-tub (الطّوب al "the" + tub "brick") "[mud] brick," which was assimilated into Old Spanish as adobe [aˈdobe], still with the meaning "mud brick." English borrowed the word from Spanish in the early 18th century.

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Adobe style in Santa Fe, New Mexico

In more modern English usage, the term "adobe" has come to include a style of architecture that is popular in the desert climates of North America, especially in New Mexico. (Compare with stucco).

Composition

An adobe brick is a composite material made of clay mixed with water and an organic material such as straw or dung. The soil composition typically contains clay and sand. Straw is useful in binding the brick together and allowing the brick to dry evenly. Dung offers the same advantage and is also added to repel insects. The mixture is roughly half sand (50%), one-third clay (35%), and one-sixth straw (15%).

Adobe bricks

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Adobe bricks near a construction site in Milyanfan, Kyrgyzstan

Bricks are made in an open frame, 25 cm (10 in) by 36 cm (14 in) being a reasonable size, but any convenient size is acceptable. The mixture is molded by the frame, and then the frame is removed quickly. After drying a few hours, the bricks are turned on edge to finish drying. Slow drying in shade reduces cracking.

The same mixture to make bricks, without the straw, is used for mortar and often for plaster on interior and exterior walls. Some ancient cultures used lime-based cement for the plaster to protect against rain damage.

The brick’s thickness is preferred partially due to its thermal capabilities, and partially due to the stability of a thicker brick versus a more standard size brick. Depending on the form that the mixture is pressed into, adobe can encompass nearly any shape or size, provided drying time is even and the mixture includes reinforcement for larger bricks. Reinforcement can include manure, straw, cement, rebar or wooden posts. Experience has shown that straw, cement, or manure added to a standard adobe mixture can all produce a stronger, more crack-resistant brick. A general testing is done on the soil content first. To do so, a sample of the soil is mixed into a clear container with some water, creating an almost completely saturated liquid. After the jar is sealed the container is shaken vigorously for at least one minute. It is then allowed to sit on a flat surface for a day or so until the soil has settled into layers or remains in suspension. Heavier particles settle out first so gravel will be on the bottom, sand above, silt above that and very fine clay and organic matter will stay in suspension for days. After the water has cleared percentages of the various particles can be determined. Fifty to 60 percent sand and 35 to 40 percent clay will yield strong bricks. The New Mexico US Extension Service recommends a mix of not more than 1/3 clay, not less than 1/2 sand, and never more than 1/3 silt. The largest structure ever made from adobe (bricks) was the Bam Citadel, which suffered serious damage (up to 80%) by an earthquake on December 26, 2003. Other large adobe structures are the Huaca del Sol in Peru, with 100 million signed bricks, the ciudellas of Chan Chan and Tambo Colorado, both in Peru.

Thermal properties

An adobe wall can serve as a significant heat reservoir due to the thermal properties inherent in the massive walls typical in adobe construction. In desert and other climates typified by hot days and cool nights, the high thermal mass of adobe levels out the heat transfer through the wall to the living space. The massive walls require a large and relatively long input of heat from the sun (radiation) and from the surrounding air (convection) before they warm through to the interior and begin to transfer heat to the living space. After the sun sets and the temperature drops, the warm wall will then continue to transfer heat to the interior for several hours due to the time lag effect. Thus a well-planned adobe wall of the appropriate thickness is very effective at controlling inside temperature through the wide daily fluctuations typical of desert climates, a factor which has contributed to its longevity as a building material. In addition, the exterior of an adobe wall can be covered with glass to increase heat collection. In a passive solar home, this is called a Trombe wall.

Adobe wall construction

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The citadel of Bam or Arg-é Bam in Kerman province of Iran: The world's largest adobe structure, dating to at least 500 BC.

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The citadel of Bam or Arg-é Bam in Kerman province of Iran: The world's largest adobe structure, dating to at least 500 BC.