Scientists uncover the secret recipe of Mayan plaster

Sap from special trees made the resulting plaster extremely resistant.
Loukia Papadopoulos
A mystic stone at the Copán ruins..jpg
A mystic stone at the Copán ruins.


Copán, an archaeological complex that can be found in the rainforests of what is now western Honduras, contains some of the most well-kept structures of all time, despite the fact that they’ve been exposed to the sun and humidity for over 1,000 years.

Now, a new paper by the University of Granada in Spain is revealing that the secret to these buildings’ longevity may lie in the plaster the Maya used to coat Copán’s walls and ceilings. The ancient architects may have used sap from the bark of local chukum and jiote trees, mixed into their plaster to reinforce their structures. 

This resulted in a material not unlike mother-of-pearl, a sturdy and resistant substance, according to a report by PopSci published on Wednesday.

“We finally unveiled the secret of ancient Maya masons,” told PopSci Carlos Rodríguez Navarro, a mineralogist at the University of Granada in Spain and the paper’s first author. 

Although throughout the years studies have indicated that many civilizations used different kinds of plasters, it is a commonly known fact that Maya plaster was one of the best and most resistant.

“Some of them perform better than others,” told PopSci Admir Masic, a materials scientist at the Massachusetts Institute of Technology who wasn’t part of the study. 

Recreating the secret recipe

Navarro and his team were curious to know what made Maya plaster so special so they used X-rays and electron microscopes to analyze brick-sized plaster chunks from Copán’s walls and floors. They discovered small amounts of organic materials like carbohydrates in the structures. 

As a next step the authors decided to make the historic plaster themselves following what they believed to be the right recipe. To do this, they sought the help of living masons and Maya descendants near Copán. 

Their inquiries led them to the specific trees whose bark the sap used in the ancient plaster came from. The end result was a pretty sturdy plaster that was also insoluble in water.

This would explain how well the Maya structures have fared despite the passing years and environmental factors.

Chukum tree sap is still mixed with cement to make water-resistant stucco to this day.

Now the researchers are further investigating if other previous civilizations could have stumbled upon the same recipe? Soon, they may have the answer for populations from Iberia to Persia to China.