A Brief History of Mortar

Ancient Beginnings

Masonry is one of the oldest skilled trades dating back over 6,000 years ago when clay bricks were used in the first shelters built in ancient Egypt. By 2550 BC the same ancient civilization, despite its primitive technology, developed the last existing 7th wonder of the ancient world– the Pyramid of Giza.

While it remains enigmatic how the ancient Egyptians were able to cut, transport and lay limestone and granite units weighing 2.5 - 80 tons from quarries up to 800km away, we do know that they used over 500,000 tons of mortar just in the construction of the Great Pyramid! For a civilization that lacked access to hydraulic power mixers and Red Bull Energy drinks, it is a baffling feat that labourers of the time mixed all of that gypsum mortar with their feet or by hand.

Functions of Mortar

The four main functions of mortar have remained the same over millennia:

-bonding of units

-weather resistance

-unit size compensation

-appearance

Components of Mortar

Lime

While the first mortars used were made of a simple mud, further advancements led to the use of gypsum mortars and later clay mortars. Eventually came the discovery of burning limestone at high temperatures (quicklime), allowing it to cool, and then soaking in water for weeks. This lime putty was then mixed with river sand, sea shells or volcanic ash to produce the world's first ever lime based mortars. These mortars were first used as early as 2450 BC (based on lime-kiln remains discovered in ancient Mesopotamia) and were adopted by most cultures. Lime based mortar was used extensively including in castle and cathedral construction all the way up to 1871.

Benefits of Lime

Prior to 1871 all masonry mortar consisted of one part lime and three parts sand or another aggregate. Lime has a low compressive strength and high elasticity in the hardened state allowing for historical buildings to shift and flex without the danger of cracking.

Manufacturing

Lime Kilns were commonly built in the early to mid 1800s into the sides of hills to haul limestone into the kilns to be fired to produce quicklime. This quicklime was then cooled and transported to job sites where the workers would have to slake, that is to soak the lime, to produce lime putty.

In the 1930s manufacturers began to produce a ready-to-use dolomitic hydrated lime that did not require the lime to be slaked on the jobsite. Hydrated lime, first developed in 1818, was a combination of limestone and clay that had a much harder resistance to water.

Roman Cement

In 1796, a new cement was developed by James Parker that was made by powdering certain clay stones and burning them. It was named “Parker cement”, and was quickly adopted as a superior mortar for the times due to its high strength.

Portland Cement

In 1824, a bricklayer in Hunslet Leeds discovered a cement by mixing calcined hard limestone with clay and then mixed it into a slurry. The mixture was then burned a second time. This cement had a similar colour to a commonly used building stone at the time that was quarried on the Isle of Portland and so it was rightfully named, “Portland cement.”

Rise to Popularity in North America

Maintaining a lower compressive strength than Roman cement, Portland cement was not as favourable despite having a faster setting time in Europe. It wasn’t until the 1860s, manufacturers in Europe discovered a strong demand for cement in North America and began to capitalise by sending ships of Portland cement filled wooden barrels to the United states. While the U.S. had their own natively produced cements, Portland quickly took over in popularity. Manufacturing of the cement in the United States quickly took off between 1871 and 1920.

The use of Portland cement in sand-lime mortars, due to its faster setting time, allowed for construction speeds to rapidly increase. With the addition of Portland cement, the mortar in the hardened state would have a significantly higher compressive strength.

Masonry Cement Mortar

By the late 1920s, in an effort to improve jobsite quality control, cement manufacturers began developing what became known as masonry cements that were ready to mix with sand and water. They contained no lime. They were formulated instead with various volumes of ground limestone (acted as a filler promoting air entrainment) and Portland cement. Manufacturers of lime considered this a serious threat to their industry and no recipe consensus could be agreed upon because at the time a harder mortar was believed to reign superior.

Mortar Type Development

Representatives of both the cement and lime industries began to develop mortar types based on different ratios of lime to cement to aggregate and were categorized based on their hardness and flexibility. In 1944, mixes dubbed A-1, A-2, B, C, and D were developed each with their own unique compressive strength. In 1951, the categorized letters were changed to take letters from the words, “MASON WORK.” The new letter designations are the same ones we use today when prescribing a particular mortar for a certain product. Those letters are type M,S,N,O and K.

Final Thoughts

Mortar has evolved drastically over the past two centuries. New admixtures and ready-mix bags come to market every year claiming to improve plasticity or accelerate curing times. At Kavanagh Masonry, we hold true to the same mortars that were developed in 1944, (renamed in 1951) as they have stood the test of time and proven their worth.

For more information on the mortars we use please reach out to us on our Request a Quote Page.

Sources

Donaghey, Kery et al. "Textbook of Canadian Masonry Second Edition"

Speweik, John P. Product Manager, GenLime Group, Genoa, Ohio