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Mortar (masonry)

technology Maturity 11-13 Next article →

Mortar is a workable paste used to bind building blocks together.

Three old bricks held together with mortar
Three old bricks held together with mortar

Builders use it to join stones, bricks, or concrete masonry units. It fills and seals the irregular gaps between these heavy blocks. This process helps spread the weight of the blocks evenly across the structure. Mortar can also be used to add decorative colors or patterns to masonry walls. While mortar becomes a rigid structure when it cures, it is usually weaker than the blocks themselves. This makes mortar a sacrificial element in masonry. Because it is less expensive and easier to repair than the building blocks, it protects the overall structure.

To create mortar, bricklayers typically mix three main ingredients: sand, water, and a binder. The binder is the substance that allows the mixture to harden. Since the early 20th century, the most common binder has been Portland cement.

This type of mortar sets very hard and very quickly. This speed allows for a faster pace of construction. It also means that fewer skilled workers are required to build a structure. However, Portland cement is not always the best choice. For example, it should not be used to repair older buildings made with lime mortar. This is because lime mortar is softer and more flexible than cement mortar.

Humans have used various types of mortar for many thousands of years.

Qorogho Barelief (3)
Qorogho Barelief (3)

The earliest mortars were made of simple mud and clay. Evidence from Jericho shows mud and clay were used in the 10th millennium BC. In 6500 BC, people in Baluchistan used mortar with sun-dried bricks. Ancient Egyptians used mud and clay for early pyramids. Later, they switched to using gypsum or lime. In China, around 500 CE, builders created a unique composite mortar. They mixed sticky rice soup with slaked lime. This mixture was stronger and more water-resistant than standard lime mortar.

Different ancient civilizations discovered how to make mortar even more durable. The Greeks used pozzolanic mortar, which is a lime-based mix containing volcanic ash.

Chetham's Library 2015 56
Chetham's Library 2015 56

This additive allows the mortar to harden even underwater, making it a hydraulic cement. The Greeks sourced this ash from islands like Thira and Nisiros. The Romans later improved these methods to build massive structures. They even developed a version using crushed terra cotta. This version included aluminum oxide and silicon dioxide. While it was not as strong as pozzolanic mortar, it was denser. This density helped the mortar resist the penetration of water.

In the United States, there are five standard types of pre-mixed mortar. These are designated by the letters M, S, N, O, and K. Interestingly, these letters come from the alternate letters in the word "MaSoN wOrK". Each type has a different strength based on its mix ratio. Type M is the strongest, with an approximate strength of 2500 psi.

Brick and block laying
Brick and block laying

In contrast, Type K is the weakest, with a strength of about 1275 psi. These standards ensure that builders use the correct strength for different construction needs.

Modern science has also introduced polymer cement mortar, or PCM. This material is made by replacing some traditional binders with polymers. These additives include things like latexes, emulsions, or liquid resins. While polymer mortar increases the cost, it enhances many properties. It is mainly designed for repairing concrete structures. It has low permeability, which means it does not let much moisture through. Researchers are even studying how to use recovered plastics to make mortars. They are looking at using PET plastics as a polymeric binder to improve mortar strength.

Mortar is also a vital tool for historians and archaeologists. As mortar hardens, it traps the atmosphere from the time it was mixed.

Chetham's Library 2015 56
Chetham's Library 2015 56

This allows scientists to use radiocarbon dating to analyze the sample. By studying the carbon trapped inside, researchers can determine the age of a building. This connection between construction materials and dating methods helps us understand the timeline of human civilization. From ancient mud walls to modern polymer mixes, mortar remains a fundamental part of how we build our world.

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🖼️ Images & Media (5)
File:Three old bricks held together with mortar.jpg
Three old bricks held together with mortar.jpg
File:Chetham's Library 2015 56.jpg
Chetham's Library 2015 56.jpg
File:Qorogho Barelief (3).jpg
Qorogho Barelief (3).jpg
File:Brick and block laying.jpg
Brick and block laying.jpg
File:Mortar mixed inside bucket.jpg
Mortar mixed inside bucket.jpg
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