Mortar (masonry)

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Mortar holding weathered bricks

Mortar is a workable paste used to bind building blocks such as stones, bricks, and concrete masonry units together, fill and seal the irregular gaps between them, and sometimes add decorative colors or patterns in masonry walls. In its broadest sense mortar includes pitch, asphalt, and soft mud or clay, such as used between mud bricks. Mortar comes from Latin mortarium meaning crushed.

Cement mortar becomes hard when it cures, resulting in a rigid aggregate structure; however the mortar is intended to be weaker than the building blocks and the sacrificial element in the masonry, because the mortar is easier and less expensive to repair than the building blocks. Mortars are typically made from a mixture of sand, a binder, and water. The most common binder since the early 20th century is Portland cement but the ancient binder lime mortar is still used in some new construction. Lime and gypsum in the form of plaster of Paris are used particularly in the repair and repointing of buildings and structures because it is important the repair materials are similar to the original materials: The type and ratio of the repair mortar is determined by a mortar analysis. There are several types of cement mortars and additives.

Ancient mortar[edit]

The first mortars were made of mud and clay. Because of a lack of stone and an abundance of clay, Babylonian constructions were of baked brick, using lime or pitch for mortar. According to Roman Ghirshman, the first evidence of humans using a form of mortar was at the Mehrgarh of Baluchistan in Pakistan, built of sun-dried bricks in 6500 BCE.[1] The ancient Harappa city in Pakistan was built in about 2600 BCE with kiln-fired bricks and a gypsum mortar. Gypsum mortar, also called plaster of Paris, was used in the construction of the Egyptian pyramids and many other ancient structures. It is made from gypsum which requires a lower firing temperature so is easier to make than lime mortar and sets up much faster which may be a reason it was used as the typical mortar in ancient, brick arch and vault construction. Gypsum mortar is not as durable as other mortars in damp conditions.[2]

In early Egyptian pyramids constructed about 2600–2500 BCE, the limestone blocks were bound by mortar of mud and clay, or clay and sand.[3] In later Egyptian pyramids, the mortar was made of either gypsum or lime.[4] Gypsum mortar was essentially a mixture of plaster and sand and was quite soft.



Hydraulic mortar was not available in ancient China, possibly due to a lack of volcanic ash. Around 500 CE, sticky rice soup was mixed with slaked lime to make an inorganic−organic composite mortar that had more strength and water resistance than lime mortar.[9][10]


Laying bricks with Portland cement mortar

Ordinary Portland cement mortar[edit]

Ordinary Portland cement mortar, commonly known as OPC mortar or just cement mortar, is created by mixing powdered Ordinary Portland Cement, aggregate and water.



Mortar mixed inside a 5 gallon bucket using clean water and mortar from a bag. When it's the right consistency as in the photo (trowel stands up) it's ready to apply.


Polymer cement mortar[edit]

Polymer cement mortars (PCM) are the materials which are made by partially replacing the cement hydrate binders of conventional cement mortar with polymers. The polymeric admixtures include latexes or emulsions, redispersible polymer powders, water-soluble polymers, liquid resins and monomers. It has low permeability, and it reduces the incidence of drying shrinkage cracking, mainly designed for repairing concrete structures. For an example see MagneLine.

Lime mortar[edit]

Main article: Lime mortar




Pozzolanic mortar[edit]

Main article: Pozzolana


Finely ground and mixed with lime is a hydraulic cement, like Portland cement, and makes a strong mortar that will also set under water.

Firestop mortar[edit]

Firestop mortars are mortars most typically used to firestop large openings in walls and floors required to have a fire-resistance rating. They are passive fire protection items. Firestop mortars differ in formula and properties from most other cementitious substances[citation needed] and cannot be substituted with generic mortars without violating the listing and approval use and compliance.

Firestop mortar is usually a combination of powder mixed with water, forming a cementatious stone which dries hard. It is sometimes mixed with lightweight aggregates, such as perlite or vermiculite[citation needed]. It is sometimes pigmented to distinguish it from generic materials[citation needed] in an effort to prevent unlawful substitution and to enable verification of the certification listing.

Radiocarbon dating[edit]

An international team headed by Åbo Akademi University has developed a method of determining the age of mortar using radiocarbon dating. As the mortar hardens, the current atmosphere is encased in the mortar and thus provides a sample for analysis. One major challenge is various factors that affect the sample and raise the margin of error for the analysis.[14]

See also[edit]


Technical data sheets, Mortar Industry Association,

  1. ^ "Ancient Bricks". Aurangzeb Khan. Retrieved 2013-02-16. 
  2. ^ "Introduction to Mortars" Cemex Corporation
  3. ^ "Egypt: Egypt's Ancient, Small, Southern, Step Pyramids". 2011-06-21. Retrieved 2012-11-03. 
  4. ^ a b "HCIA - 2004". Retrieved 2012-11-03. 
  5. ^ O. P. Jaggi, History of science and technology in India, Volume 1, Atma Ram, 1969, ... In some of the important-looking buildings, gypsum cement of a light gray colour was used on the outside to prevent the mud mortar from crumbling down. In a very well constructed drain of the Intermediate period, the mortar which was used contains a high percentage of lime instead of gypsum. Bitumen was found to have been used only at one place in Mohenjo-daro. This was in the construction of the great bath ... 
  6. ^ Abdur Rahman, History of Indian science, technology, and culture, Oxford University Press, 1999, ISBN 978-0-19-564652-8, ... Gypsum cement was found to have been used in the construction of a well in Mohenjo-daro. The cement was light grey and contained sand, clay, traces of calcium carbonate, and a high percentage of lime ... 
  7. ^ [1]
  8. ^ "American Scientist Online". Retrieved 2012-11-03. 
  9. ^ "Revealing the Ancient Chinese Secret of Sticky Rice Mortar". Science Daily. Retrieved 23 June 2010. 
  10. ^ Fuwei Yang, Bingjian Zhang, and Qinglin Ma, ‘’ Study of Sticky Rice−Lime Mortar Technology for the Restoration of Historical Masonry Construction’’, Acc. Chem. Res., 2010, 43 (6), pp 936–944
  11. ^ Masonry: the best of Fine homebuilding.. Newtown, CT: Taunton Press, 1997. Print. 113.
  12. ^
  13. ^ "pozzolana." Collins English Dictionary - Complete & Unabridged 10th Edition. HarperCollins Publishers. 14 May. 2014. <>
  14. ^ Dating Ancient Mortar - American Scientist Online vol. 91, 2003