Archaeologists discovered the secret ingredient that made Mayan plaster durable

Ancient Mayan masons had their own secrets for making lime plasters, mortars, and plasters, which they used to build their magnificent structures, many of which still stand today.

A team of mineralogists and geologists at the University of Granada has discovered the secret ingredient that made Mayan plaster so durable.

The team has analyzed samples of Maya plasters from Honduras and confirmed that the Maya added plant extracts to improve the plasters’ performance, according to a new paper published in the journal Science Advances.

The team collaborated with local Maya-descended masons in Copán, Honduras, which was a major Maya center prior to Spanish colonization of Central America, to learn how the plaster was made. The approach involves adding the sap from the bark of local tree species, Chukum and Jiote when the lime – the umbrella term for calcium oxides rather than the delicious fruit – is mixed with water, a process called slaking.

A comparison of plaster and stucco from 540 to 850 CE and those created by the team today reveals a striking resemblance. Maya masons most likely used sap-infused plaster because of its increased durability, plasticity, and water resistance.

Since ancient times, and in some cases even earlier, plaster, cement, and concrete have been used. These now-ubiquitous building materials have been used and improved by numerous civilizations, but not always the exact recipes used by our forebears are passed on intact, as in this instance. Archaeologists occasionally have to put in a lot of effort to understand how these materials were made.

“Our study helps to explain the improvement in the performance of lime mortars and plasters with natural organic additives developed not only by ancient Maya masons but also by other ancient civilizations (e.g., ancient Chinese sticky rice lime mortars),” the authors wrote in the paper.

The study is published in Science Advances.

DOI: 10.1126/sciadv.adf6138