Ancient Maya masons had a smart way to make plaster stronger

Date:
Wed, 19 Apr 2023 18:16:42 +0000

Description:
The idols, pyramids, and dwellings in the ancient Maya city of Copn have lasted longer than a thousand years. DEA/V. Giannella/Contributor via Getty Images Up close, the Mayas' timeless recipe from Copn looks similar to mother-of-pearl. The post Ancient Maya masons had a smart way to make plaster stronger appeared first on Popular Science .

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The idols, pyramids, and dwellings in the ancient Maya city of Copn have lasted longer than a thousand years. DEA/V. Giannella/Contributor via Getty Images

An ancient Maya city might seem an unlikely place for people to be experimenting with proprietary chemicals. But scientists think thats exactly what happened at Copn, an archaeological complex nestled in a valley in the mountainous rainforests of what is now western Honduras.

By historians reckoning, Copns golden age began in 427 CE, when a king named Yax Kuk Mo came to the valley from the northwest. His dynasty built one of
the jewels of the Maya world, but abandoned it by the 10th century, leaving its courts and plazas to the mercy of the jungle. More than 1,000 years
later, Copns buildings have kept remarkably well, despite baking in the tropical sun and humidity for so long.

The secret may lie in the plaster the Maya used to coat Copns walls and ceilings. New research suggests that sap from the bark of local trees, which Maya craftspeople mixed into their plaster, helped reinforce its structures. Whether by accident or by purpose, those Maya builders created a material not unlike mother-of-pearl , a natural element of mollusc shells.

We finally unveiled the secret of ancient Maya masons, says Carlos Rodrguez Navarro , a mineralogist at the University of Granada in Spain and the papers first author. Rodrguez Navarro and his colleagues published their work in the journal Science Advances today.

[Related: Scientists may have solved an old Puebloan mystery by strapping giant logs to their foreheads ]

Plaster makers followed a fairly straightforward recipe. Start with carbonate rock, such as limestone; bake it at over 1,000 degrees Fahrenheit; mix in water with the resulting quicklime; then, set the concoction out to react
with carbon dioxide from the air. The final product is what builders call
lime plaster or lime mortar.

Civilizations across the world discovered this process, often independently. For example, Mesoamericans in Mexico and Central America learned how to do it by around 1,100 BCE. While ancient people found it useful for covering surfaces or holding together bricks, this basic lime plaster isnt especially durable by modern standards. Copn, with its temples, squares, terraces and other characteristics, is an excellent representation of Classic Mayan civilization. Xin Yuewei/Xinhua via Getty Images

But, just as a dish might differ from town to town, lime plaster recipes varied from place to place. Some of them perform better than others, says Admir Masic , a materials scientist at the Massachusetts Institute of Technology who wasnt part of the study. Maya lime plaster, experts agree, is one of the best.

Rodrguez Navarro and his colleagues wanted to learn why. They found their first clue when they examined brick-sized plaster chunks from Copns walls and floors with X-rays and electron microscopes. Inside some pieces, they found traces of organic materials like carbohydrates.

That made them curious, Rodrguez Navarro says, because it seemed to confirm past archaeological and written records suggesting that ancient Maya masons mixed plant matter into their plaster. The other standard ingredients (lime and water) wouldnt account for complex carbon chains.

To follow this lead, the authors decided to make the historic plaster themselves. They consulted living masons and Maya descendants near Copn. The locals referred them to the chukum and jiote trees that grow in the surrounding forestsspecifically, the sap that came from the trees bark. Bursera simaruba , sometimes locally known as the jiobe tree. Deposit Photos

The authors tested the saps reaction when mixed into the plaster. Not only
did it toughen the material, it also made the plaster insoluble in water, which partly explains how Copn survived the local climate so well.

The microscopic structure of the plant-enhanced plaster is similar to nacre
or mother-of-pearl: the iridescent substance that some molluscs create to
coat their shells. We dont fully understand how molluscs make nacre , but we know that it consists of crystal plates sandwiching elastic proteins. The combination toughens the sea creatures exteriors and reinforces them against weathering from waves.

A close study of the ancient plaster samples and the modern analog revealed that they also had layers of rocky calcite plates and organic sappy material, giving the materials the same kind of resilience as nacre. They were able to reproduce what living organisms do, says Rodrguez Navarro.

This is really exciting, says Masic. It looks like it is improving properties [of regular plaster].

Now, Rodrguez Navarro and his colleagues are trying to answer another question: Could other civilizations that depended on masonryfrom Iberia to Persia to Chinahave stumbled upon the same secret? We know, for instance,
that Chinese lime-plaster-makers mixed in a sticky rice soup for added strength.

Plaster isnt the only age-old material that scientists have reconstructed. Masic and his colleagues found that ancient Roman concrete has the ability to self-heal. More than two millennia ago, builders in the empire may have added quicklime to a rocky aggregate, creating microscopic structures within the material that help fill in pores and cracks when its hit by seawater.

[Related: Ancient architecture might be key to creating climate-resilient buildings ]

If that property sounds useful, modern engineers think so too. There exists a blossoming field devoted to studyingand recreatingmaterials of the past . Standing structures from archaeological sites already prove they can
withstand the test of time. As a bonus, ancient people tended to work with more sustainable methods and use less fuel than their industrial
counterparts.

The Maya paperis another great example of this [scientific] approach, Masic says.

Not that Maya plaster will replace the concrete thats ubiquitous in the
modern worldbut scientists say it could have its uses in preserving and upgrading the masonry found in pre-industrial buildings. A touch of plant sap could add centuries to a structures lifespan.

The post Ancient Maya masons had a smart way to make plaster stronger
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Link to news story:
https://www.popsci.com/science/ancient-maya-plaster/


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