Pre-Pottery Neolithic B (PPNB) residents of Motza, Israel were using dolomite in their plaster some 8,000 years before the Romans did, according to a recent study published in the Journal of Archaeological Science, making it the oldest known case of the technique being used.

Evidence of calcium carbonate-based plaster dates back to as long as 10,000 to 12,000 years ago, though later became a dominent building material used by many ancient civilizations. However, after Motza, the dolomite-based plaster seems to have been lost, until it was later picked up by the Romans.

Analysis of plaster discovered during excavations between 2015 and 2021 at Motza (which dates to around 7,100–6,700 BCE) found traces of fired dolomite mixed into the plaster - when, at the time, standard plaster was made from calcite, the mineral form of calcium carbonate found in limestone.

In order to make plaster, the study explained, residents of Motza would heat the stone and then slake it with water to create the lime, turning it into a versatile binder that hardens as it reabsorbs carbon dioxide from the air.

However, at Motza, which sits on a dolomite bedrock (a harder rock containing calcium and magnesium) craftspeople decided to use materials easily found on hand.

Archaeologists at the site found shallow fire pits, around 1.5 to 2.6 meters in diameter and some 50 centimeters deep, filled with burnt stones set near the plaster floors.

One of the pits found held calcite stones, while its adjacent pit held dolomite in a separation the study agued was intentional, as making lime from dolomite is a more demanding process than making it from calcite.

According to the study, the main difference is controlling the firing temperatures. If the fire burns too hot, the dolomite is fully broken down into unstable oxides, and if it is too cool, the reaction never starts, meaning that finding and maintaining the perfect temperature (under 900 degrees Celcius) is crucial.

"The Pre-Pottery Neolithic B residents of Motza were surprisingly able to differentiate calcite and dolomite stones and used both in their plaster making," the study said.

Archaeologists at the site found two separate types of dolomitic plaster floors.

In one, the dolomite was used only as an aggregate material, quickly crushed and added to the calcitic-plaster mix.

In the other, dolomite used in the base layers of the plaster had reformed as crystals, most likely after being fired and water being added, incdicated a “complete dolomite-lime cycle," according to the study, making it stronger and more water-resistant than ordinary lime plaster.

"Using dolomite for plaster making can have several advantages," wrote the study. "First, if you are in a dolomite-rich area, you save on the cost and effort of bringing in calcite; secondly, dolomite calcines at a lower temperature than calcite, so you can save fuel; thirdly, it can produce stronger and more water-resistant plaster."

"They not only used dolomite as an aggregate but developed and perfected the use of dolomite in the binder despite technical difficulties. They may have successfully made dolomitic plaster where dolomite is fully recrystallized along with the calcite, something that to our knowledge has not been observed anywhere else."