The word adobe has meant mud brick for roughly four thousand years
Ancient Egyptians wrote a word for mud brick around 2000 BC. It passed into Coptic, then Arabic, then Spanish, and finally English, barely changing in sound or sense along the way. The material behind it, sun-dried earth and straw, is among humanity's oldest building methods and still shelters people worldwide.
Adobe bricks are unfired blocks of earth, water and usually some straw or dung. The organic fibre helps a brick shrink evenly as it dries, so it does not crack. A good mix is roughly 15% clay with silt and plenty of fine sand, and no more than half the clay should be the expansive kind. The mud is packed into wooden moulds, turned out, dried for several days, then stood on edge to finish curing. Sizes vary by region; one New Mexico State University guide lists bricks weighing about 13 to 27 kilograms.
Builders have used it for a very long time. Adobe architecture predates 5,100 years ago, and sun-dried earth buildings are found from West Africa and the Middle East to the Andes and eastern Europe. Indigenous peoples of the American Southwest, Mesoamerica and the Andes built with it for millennia; Puebloan builders shaped walls from handfuls or basketfuls of mud until the Spanish brought moulded bricks. Spain itself had used adobe bricks since the eighth century BCE.
Its great strength is thermal mass. Thick walls soak up the day's heat slowly and release it after dark, smoothing out the swing between hot days and cold nights. Walls are load-bearing, rarely rise beyond two storeys, and are traditionally laid in mud mortar and coated with mud or lime plaster, since hard cement coatings can speed decay. Earthquakes are the weakness: unreinforced adobe suffered heavily in Guatemala in 1976, Bam in 2003 and Chile in 2010.
Modern builders sometimes stabilise the mix with asphalt emulsion or Portland cement. During the Great Depression Hugh W. Comstock devised a cheap version he called Bitudobe, built his first adobe house in 1936, and in 1948 published a book on his timber-framed post-adobe system.
Source: Adobe
