What is Mortar?

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  • Written By: C. Ausbrooks
  • Edited By: Bronwyn Harris
  • Last Modified Date: 14 October 2019
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Mortar is a paste used to bind blocks together while filling the spaces between them. It is used most commonly in the masonry trade to bind stone, brick or concrete blocks during building construction. It can also be used to repair when the original application has crumbled or washed away.

Mortar is a combination of sand, a binder such as lime or concrete, and water. It is applied as a thick paste and sets hard. It creates a tight seal between bricks to prevent the entry of air and moisture into the structure. It bonds with any joint reinforcements, anchor bolts or metal ties, and compensates for size variations in the bricks to create an aesthetically pleasing and structurally sound building.

The first mortar used by man was nothing more than mud or clay combined with water. The ancient Egyptian pyramids, dating back to 2600 BCE, were made of limestone bricks bound together with mud and clay. Eventually, concrete mortar came into popular use. Today, there are several different kinds of mortar available for all types of building and construction.

Portland cement mortar (OPC) is a mixture of Portland cement, sand and water. Joseph Aspdin created OPC in 1794 and received a patent for the mixture in 1824. It was used heavily in the late 19th century and by 1930, it was used exclusively in new construction. It sets quickly, requires less skill to use, and increases construction speed.


Polymer cement mortar (PCM) is created by replacing cement binders of traditional mortar with polymers. These include latex, emulsions, powders, liquid resins, water-soluble polymers and monomers. PCM reduces shrinkage cracking and is primarily used for repairing concrete construction.

Lime mortar is created by placing impure lime stones in a kiln. The resulting dust is a hydraulic lime that sets almost instantly upon contact with water. It is used as a binder in the mortar mixture instead of concrete or polymers. Lime mortar is breathable when set, and allows moisture to move freely and evaporate from the surface.

Mortar is hard wearing and typically lasts a very long time, even without repair. The standard lifespan of modern mortar is around 20-30 years. It may need replacing or refreshing if it easily scraped out with a sharp knife.


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Post 2

It is hard to believe the pyramids were put together with mud and water mortar. It makes you wonder if all of our new forms of building materials are really any better. Even so, I guess I also would not want to live in a house made of a mortar mix that was basically wet dirt.

Post 1

I had no idea there were so many kinds of mortar. I really thought that it wasjust a mixture of lime with cement, sand, and water. I knew it was used in building to bond bricks or stones, but never saw it much growing up on the beach. I guess that the styles of making a structurally sound building really vary based on the environment and the resources available, huh?

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