Sticky Rice Keeps the Great Wall Standing

The Great Wall of China. (Image: dvillaret Flickr via Compfight cc)
The Great Wall of China. (Image: dvillaret Flickr via Compfight cc)

The Great Wall of China has remained standing for thousands of years thanks to mortar made from sticky rice soup mixed with the standard mixture of slaked lime. This kind of mortar is even stronger and more waterproof than cement. According to scientists, the section of the Great Wall that is still standing owes its strength to the use of this sticky rice mortar.

According to research, sticky rice can be used to produce a super-strong mortar. The researchers found that in ancient China, builders used the material to construct tombs, pagodas, city walls, and buildings, some of which still exist today.

Some of these structures have survived strong earthquakes, and it was found that even modern bulldozers had difficulty tearing them down. Zhang Bingjian, a Chinese scientist, said that sticky rice mortar was one of the greatest technological innovations in history, being stronger and more water-resistant than traditional lime mortar.

Archaeologists discovered that before the Shang Dynasty, people used reeds and yellow mud to construct the Great Wall. From the Zhou Dynasty onward, the method gradually changed to a rammed-earth type of construction using lime compacted with earth, sand, and small stones.

In the 5th century, during the period of the Northern and Southern dynasties, people used a combination of lime, clay, and sand. They found that in the right proportion, these three ingredients mixed with water to form a sticky substance that dries to be very hard.

It was used to repair walls, tombs, and other structures. This formula underwent improvements over thousand of years and was still in use in the 20th century.

At some time during the Northern and Southern dynasties, the magical effects of sticky rice as a building material were discovered, leading to the invention of sticky rice mortar.

Sticky rice is an important staple food in southern China. The Northern people called it “Jiangmi” in Chinese. It is different from ordinary rice. When cooked, the grains stick together, and when dehydrated, they become very stiff. Perhaps these properties are what inspired ancient people to use sticky rice for construction.

Sticky rice is an important staple food in Southern China (Photo Credit: thomaswanhoff Flickr via Compfight cc)

Sticky rice is an important staple food in Southern China (Image: thomaswanhoff Flickr via Compfight cc)

Sticky rice was “the binder of binders.” Artisans boiled it until it became sticky, and then thoroughly mixed it with lime, clay, and sand to form mortar. When it dried, it was much tougher and more water-resistant than regular mortar.

Using sticky rice mortar when laying bricks made buildings exceptionally strong and more durable. In Quanzhou, a city in Fujian Province, pagodas and bridges built during the Tang and Song dynasties have withstood earthquakes up to 7.5 in magnitude.

In Quanzhou and other cities, including Nanjing and Xi’an, ancient city walls built during the Ming Dynasty still stand tall and strong after more than 600 years. Also in Nanjing, a tomb built during the Ming Dynasty was discovered. Even shovels, drills, bulldozers, and hydraulic excavating equipment had difficulty in breaking it open during the excavation in 1978.

Pagoda in Quanzhou (Photo Credit: scotted400 Flickr via Compfight cc)

Pagoda in Quanzhou. (Image: scotted400 Flickr via Compfight cc)

After the Song and Yuan dynasties, the use of sticky rice mortar became more mature. The famous Forbidden City in Beijing, the stretch of Great Wall built during the Ming Dynasty, the Chengde Mountain Resort, the Eastern Qing tombs, and the Qiantang River wall built during the Ming and Qing dynasties were all projects built using it. Even after hundreds of years, these structures are still in good condition.
The Fujian Tulou (literally “earthen buildings”) are famous for their durability. Some of these buildings were constructed using sticky rice mixed with lime, clay, sand, sugar, and other organic substances, making the walls as strong as cement.

Fujian Tulou (literally, "earthen buildings") (Photo Credit: snotch Flickr via Compfight cc)

Fujian Tulou (literally, “earthen buildings”). (Image: snotch Flickr via Compfight cc)

In ancient China, feeding the people was a top priority for society, so sticky rice mortar was reserved for high-end structures, and was never as widely used as ordinary mortar. Using sticky rice for construction was considered a waste, especially during times of limited agricultural output and frequent natural disasters.

Even during the Ming Dynasty, when the emperor moved the capital to the city now known as Beijing, repair to the city wall was made with regular mortar.

Translated by: Chua BC, edited by Mikel Davis

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