Mud brick (adobe) is an ancient building material. Under favorable conditions, the crumbled remains of adobe buildings 10,000 years old have been found and authoritatively dated. In addition to small adobe buildings, people were just beginning to do a little gardening, to construct burial mounds, and to make sun- dried pottery. It is interesting that sun-dried adobe construction developed approximately concurrently with early sun-dried pottery.
The ruins of the oldest adobe brick buildings in the Americas have been discovered in the Chao Valley of northern Peru, between the Pacific Ocean and the Andes Mountains. They date from around 5,000 years ago. That was about the time that Upper Egypt (counterintuitively, Upper Egypt is south of the Aswan cataracts) and Lower Egypt (from Aswan north to the Mediterranean) were being unified under the kings of the First Dynasty. When the adobe buildings of the Chao Valley were being constructed the Great Pyramid of Giza, assembled from granite and limestone, was only 500 years old. Adobe is indeed an ancient building material.
Historic mud brick homes going back more than a century, are still standing and in current service. The Avila Adobe was built on Olvera Street in Los Angeles, by Francisco Avila in 1818. It remains in place today. General Andres Pico, once head of the Mexican army in Alta California, had a home built in the San Fernando Valley, roughly where the Golden State Freeway and the San Diego Freeway now intersect. General Pico’s former home is still standing.
Old adobe buildings, still in use, are found not just in California. The Historic Taos Inn in New Mexico consists partially of adobe houses dating from the 1800’s. It remains entirely functional. As this is written Expedia.com quotes mid-week room rates of $200 for a double bed at the Taos Inn. Their compelling advertisement assures the interested excursionist that “… sheets are included.”
Traditional adobe is an admixture of 50-70% sand with the balance being clay or silt in approximately equal proportions and seasoned with straw (see Exodus 5). These elements are mixed with water to form a thick mud before being pressed into wooden brick-forms and left to dry in the sun, sometimes for a month or more. The straw helps bind the water, clay, and sand
together and allows the compound to dry with minimal cracks. When dry, the bricks are tested for strength. The test is uncomplicated: drop the individual adobe brick from knee height. If it doesn’t break, it’s good enough.
Since adobe construction is heavy, its foundation is subject to settling and may result in cracked walls. The settling is due to seasonal expansion and contraction of the soil beneath the building’s foundation. Consequently, it was the practice of early mission builders to set foundation depth below the frost level, where seasonal changes are minimal.
The foundation of adobe bricks was, at first, simply laid upon a course of water- smoothed rocks. Later the bricks were placed upon a foundation of stone and masonry, the better to support the heavy adobe walls.
The same mud mixture, but a little more liquid and without the straw, is referred to as puddle adobe. It is used both as a mortar between adobe bricks and as a protective layer over them. When the sacrificial mixture shows wear from the effects of weather (exterior walls) or use (interior walls), it is time to re-plaster, thus prolonging the life of the underlying bricks and ultimately, the entire structure.
Passive heating / cooling:
With its relatively weak compressive and lateral strength, adobe construction requires thick load bearing walls which, in turn, maximize adobe’s passive temperature moderation effects. The desert climates, where adobe is most common, are characterized by hot days and cool nights. Thermal radiation from thick adobe walls naturally cool the building’s interior during the day and radiate warmth in the evenings. The effectiveness of adobe’s temperature moderation contributes to its historical desirability in the extremes of desert climates.
Roofs were traditionally flat with a slight slope that permitted drainage from seasonal rains. If the roof had a perimeter wall (parapet) there would likely be scuppers that drained into water barrels.
Early mission roofs were formed in three layers by (i) laying beams of wood spanning the building. The ends were attached to the tops of the walls. A latticework of (ii) small wooden braces would be placed crosswise atop the heavier beams. Brush was (iii) laid on the braces and sealed with “puddle” adobe. Puddle adobe is not used for bricks: it is used to prevent and seal leaks.
Roof design evolved around the first third of the 1800’s. The new approach was to first apply about three inches of puddle adobe atop the latticework (layer ii, above), then 18 inches of dry adobe dirt. The dirt was contoured into small “ditches” that slopped to a scupper. When it rained, the clay particles within the puddle adobe would expand and create something similar to a waterproof membrane. Annual maintenance amounted to pulling the weeds from the roof and re-sloping the dirt.
Eventually, roof coverings advanced to become tile, either flat or barrel. Most older adobe buildings were eventually retrofitted with tile roofs, so it is difficult to estimate age by considering only the building’s roof.
Domestically, the Uniform Building Code of 1927 continued to authorize adobe construction but (i) limited building height to one story, (ii) improved the adobe mix to provide minimum compressive and shear strengths, and (iii) required building plans to account for seismic activity.
That all ended in the 1980s when seismic related changes in the California Building Code ended solid wall adobe construction in California.
Due to its low structural strength, adobe is seldom found in buildings, even ancient buildings, more than three stories high. For this reason, when a big building is needed, the footprint occupies an appropriately wide site. Instead of being built high, adobe buildings are built wide.
An interesting exception to low-rise adobe buildings was the Arg-e Bam, a 2,500- year-old fortress / administrative center / bazaar / residential community destroyed on December 26th, 2003, when the city of Bam was devastated by a 6.6 (Richter) earthquake. More than 26,000 people were killed, and another 30,000 injured. References to Arg-e Bam in this article refer to the pre-earthquake structure.
The Arg-e Bam sat on the southern edge of the Iranian high plateau and was made habitable by snowmelt flowing into a seasonal river. The river water was delivered to Arg-e Bam through gravity flow, and thence into underground aqueducts and cisterns.
Gravity flow is an early way of getting water from where it is to where it is wanted. Its success depends upon the ground slope. In the example of Arg-e Bam the water enters the aqueducts at an elevation enough above the fortress that the flow of water was all downhill. No pumping was required. Public fountains were kept full by gravity alone. This was how water was brought to Rome 5,000 years ago. It is how Frederick Eaton and William Mulholland later brought water from the Owens Valley to Los Angeles (see Something to Think About #112).
Arg-e Bam, prior to the 2003 earthquake.
The Arg-e Bam is said to be the largest adobe building ever built (per Wikipedia.org). Constructed by the early Persians between 600 and 400 BCE, it totaled just under 2 million square feet (Gross Leasable Area). To place this in perspective, the Woodfield Mall (Schaumburg, Illinois), the 15th largest regional shopping center in the United States, consists of a bit under 2.2 million sq. ft. GLA. The Galleria (Glendale, CA), another regional center, has 1.6 million sq. ft. GLA. The Arg-e Bam, hand-built 2,500 years ago out of mud bricks, was roughly the size of a contemporary regional shopping center.
Missions were considered temporary ventures by the Spanish hierarchy. They were multi-purpose construction. They were required to be self-sufficient in food and water, to house the clergy and to provide a confined space for (sometimes) aggressive conversions to be tested. The Spanish missions were the first large-scale farms and ranches in California. Commonly raised grains were wheat, corn and barley. These were ground into flour and made into bread. Orange and lemon trees were cultivated. Animals were raised not only for their meat but also for leather and wool and their ability to enrich the soil. But records suggest some animals were considered more desirable than others. For example, in 1832 the missions collectively owned 151,000 cattle and 137,000 sheep. The third most numerous domesticated animal was the horse, but there were only 14,500 of them.
The Spanish missions maintained authority over the indigenous people until the mid-1820s. From 1824 to 1834 the Mexican government handed out 51 grants of land that (i) had belonged to Indians and (ii) were currently held by missions. Between 1834 and 1836 the Mexican government revoked the power of the Franciscans to use Indians as compulsory labor. The California missions were secularized in 1833, when the Mexican Secularization Act seized the former mission lands and converted them into expansive ranchos.
This article is for informational purposes only and is not intended as professional advice. Klarise Yahya is not a financial planner. Nothing in this article is presented as investment guidance. For specific circumstances, please contact an appropriately licensed professional. Klarise Yahya is a Commercial Mortgage Broker specializing in difficult-to-place mortgages for any
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