Natural Science in Archaeology

11.5 Mud Brick, Terracotta, and Other Earthen Architectural Materials 269
Egyptian architecture, gypsum was used as a lubricant for sliding megalithic blocks
into place rather than to hold them together. In other forms of construction, mortar
plays a significant role in consolidation of the masonry construction. In Roman
architecture, some types of walls were merely stone veneers that depended on
cement to hold the masonry together. Mortars can play a significant role in reducing
moisture infiltration, thus impeding freeze-thaw damage.
11.5 Mud Brick, Terracotta, and Other Earthen
Architectural Materials
Earth mixed with water and various additives has been used as a building material for
more than 10,000 years and is still in use. More than one-third of the world’s population
is still living in adobe and similar structures (Sumanov 1990). Earthen building
materials were traditionally utilized by a wide variety of peoples in a vast array of
geologic contexts and geographical locations including Africa, Asia, Europe, North
America, and South America. Earthen architecture was used not only for humble
residences, but also for monumental works by many of the ancient world’s great
civilizations. The ancient city of Nineveh had major mud-brick structures. Unfortunately,
little remains of Nineveh except a pile of amorphous earthen material.
Earthen architectural materials are used primarily in climates with relatively low
annual rainfall. The earthen material must be continually repaired as it disaggregates.
Ancient remains tend to be those that have been either continuously occupied,
and thus maintained, or have been somehow protected from the rain. Despite
the increasing popularity of modern construction materials, the tradition of earthen
construction has continued. As a result, archaeologists and architectural historians
have been able to make many inferences regarding ancient mud-brick technology
based on recent constructions. Famous examples of monumental earthen architecture
include the great mosque at Djenne in Mali (ca. 1907) and the mud-brick cities
of the Arabian Peninsula, whose multi-level apartment buildings have been continuously
repaired for centuries (Leslie 1991).
Most, although not all, earthen construction materials are processed mixtures
containing components from various sources. Ancient builders learned through
trial and error that the addition of certain additives could affect plasticity, durability,
and shrinkage of the material. Calcium carbonate is still a widely used binder.
Its chief advantage is that it controls shrinkage in montmorillonite clays. Other
traditional additives such as egg albumen and blood reportedly improve moisture
resistance and may also have symbolic importance in some cultures. Straw controls
shrinkage, acts as a binder, and makes the earth mixture lighter by introducing tiny
air spaces.
There are many varieties of earthen masonry, with as many local names for the
materials. However, earthen masonry products can be generally divided into the
following categories: mounded earth, rammed earth, unbaked clay or mud, and
sun-dried mud brick.