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Mortar is a workable paste which hardens to bind building blocks such as
stones In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...
,
brick A brick is a type of construction material used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a unit primarily composed of clay. But is now also used informally to denote building un ...
s, and
concrete masonry unit A concrete block, also known as a cinder block in North American English, breeze block in British English, or concrete masonry unit (CMU), or by various other terms, is a standard-size rectangular block used in building construction. The ...
s, to fill and seal the irregular gaps between them, spread the weight of them evenly, and sometimes to add decorative colours or patterns to
masonry Masonry is the craft of building a structure with brick, stone, or similar material, including mortar plastering which are often laid in, bound, and pasted together by mortar (masonry), mortar. The term ''masonry'' can also refer to the buildin ...
walls. In its broadest sense, mortar includes pitch, asphalt, and soft clay, as those used between bricks, as well as cement mortar. The word "mortar" comes from the
Old French Old French (, , ; ) was the language spoken in most of the northern half of France approximately between the late 8th [2-4; we might wonder whether there's a point at which it's appropriate to talk of the beginnings of French, that is, when it wa ...
word ''mortier'', "builder's mortar, plaster; bowl for mixing." (13c.). Cement mortar becomes hard when it cures, resulting in a rigid aggregate (composite) , aggregate structure; however, the mortar functions as a weaker component than the building blocks and serves as the sacrificial element in the masonry, because mortar is easier and less expensive to repair than the building blocks.
Bricklayer A bricklayer, which is related to but different from a mason, is a craftsperson and tradesperson who lays bricks to construct brickwork. The terms also refer to personnel who use blocks to construct blockwork walls and other forms of maso ...
s typically make mortars using a mixture of
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
, a binder, and water. The most common binder since the early 20th century is
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...
, but the ancient binder lime (producing
lime mortar Lime mortar or torching is a masonry mortar (masonry), mortar composed of lime (material), lime and an construction aggregate, aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, used in ancient Rome and anci ...
) is still used in some specialty new construction. Lime, lime mortar, and gypsum in the form of
plaster of Paris Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of buildings, while "re ...
are used particularly in the repair and repointing of historic buildings and structures, so that the repair materials will be similar in performance and appearance to the original materials. Several types of cement mortars and additives exist.


Ancient mortar

The first mortars were made of mud and
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
, as demonstrated in the 10th millennium BC buildings of
Jericho Jericho ( ; , ) is a city in the West Bank, Palestine, and the capital of the Jericho Governorate. Jericho is located in the Jordan Valley, with the Jordan River to the east and Jerusalem to the west. It had a population of 20,907 in 2017. F ...
, and the 8th millennium BC of Ganj Dareh. According to Roman Ghirshman, the first evidence of humans using a form of mortar was at the
Mehrgarh Mehrgarh is a Neolithic archaeological site situated on the Kacchi Plain of Balochistan, Pakistan, Balochistan in Pakistan. It is located near the Bolan Pass, to the west of the Indus River and between the modern-day Pakistani cities of Quetta, ...
of Baluchistan in what is today Pakistan, built of sun-dried bricks in 6500 BC. Gypsum mortar, also called plaster of Paris, was used in the construction of many ancient structures. It is made from gypsum, which requires a lower firing temperature. It is therefore 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. In the
Indian subcontinent The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...
, multiple cement types have been observed in the sites of the
Indus Valley civilization The Indus Valley Civilisation (IVC), also known as the Indus Civilisation, was a Bronze Age civilisation in the northwestern regions of South Asia, lasting from 3300  BCE to 1300 BCE, and in its mature form from 2600 BCE ...
, with gypsum appearing at sites such as the
Mohenjo-daro Mohenjo-daro (; , ; ) is an archaeological site in Larkana District, Sindh, Pakistan. Built 2500 BCE, it was one of the largest settlements of the ancient Indus Valley Civilisation, and one of the world's earliest major city, cities, contemp ...
city-settlement, which dates to earlier than 2600 BC. Gypsum cement that was "''light grey and contained sand, clay, traces of calcium carbonate, and a high percentage of lime''" was used in the construction of wells, drains, and on the exteriors of "''important looking buildings''." Bitumen mortar was also used at a lower-frequency, including in the Great Bath at Mohenjo-daro. In early Egyptian pyramids, which were constructed during the Old Kingdom (~2600–2500 BC), the limestone blocks were bound by a mortar of mud and clay, or clay and sand. In later Egyptian pyramids, the mortar was made of gypsum, or lime. Gypsum mortar was essentially a mixture of plaster and
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
and was quite soft. 2nd millennium
Babylonia Babylonia (; , ) was an Ancient history, ancient Akkadian language, Akkadian-speaking state and cultural area based in the city of Babylon in central-southern Mesopotamia (present-day Iraq and parts of Kuwait, Syria and Iran). It emerged as a ...
n constructions used lime or pitch for mortar. Historically, building with
concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
and mortar next appeared in
Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
. The excavation of the underground aqueduct of Megara revealed that a reservoir was coated with a pozzolanic mortar 12 mm thick. This aqueduct dates back to c. 500 BC. Pozzolanic mortar is a lime based mortar, but is made with an additive of volcanic ash that allows it to be hardened underwater; thus it is known as hydraulic cement. The Greeks obtained the volcanic ash from the Greek islands Thira and Nisiros, or from the then Greek colony of Dicaearchia ( Pozzuoli) near Naples, Italy. The Romans later improved the use and methods of making what became known as pozzolanic mortar and cement. Even later, the Romans used a mortar without pozzolana using crushed terra cotta, introducing aluminum oxide and
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
into the mix. This mortar was not as strong as pozzolanic mortar, but, because it was denser, it better resisted penetration by water. 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 Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed with water. Annually, approxim ...
to make an inorganic−organic composite sticky rice mortar that had more strength and water resistance than lime mortar. It is not understood how the art of making hydraulic mortar and cement, which was perfected and in such widespread use by both the Greeks and Romans, was then lost for almost two millennia. During the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...
when the Gothic cathedrals were being built, the only active ingredient in the mortar was lime. Since cured
lime mortar Lime mortar or torching is a masonry mortar (masonry), mortar composed of lime (material), lime and an construction aggregate, aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, used in ancient Rome and anci ...
can be degraded by contact with water, many structures suffered over the centuries from wind-blown rain.


Ordinary Portland cement mortar

''Ordinary Portland cement mortar'', commonly known as OPC mortar or just cement mortar, is created by mixing powdered ordinary Portland cement, fine aggregate and water. It was invented in 1794 by Joseph Aspdin and patented on 18 December 1824, largely as a result of efforts to develop stronger mortars. It was made popular during the late nineteenth century, and had by 1930 became more popular than lime mortar as construction material. The advantages of Portland cement is that it sets hard and quickly, allowing a faster pace of construction. Furthermore, fewer skilled workers are required in building a structure with Portland cement. As a general rule, however, Portland cement should not be used for the repair or repointing of older buildings built in lime mortar, which require the flexibility, softness and breathability of lime if they are to function correctly. In the United States and other countries, five standard types of mortar (available as dry pre-mixed products) are generally used for both new construction and repair. Strengths of mortar change based on the mix ratio for each type of mortar, which are specified under the
ASTM ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...
standards. These premixed mortar products are designated by one of the five letters, M, S, N, O, and K. Type M mortar is the strongest, and Type K the weakest. The mix ratio is always expressed by volume of \text. These type letters are taken from the alternate letters of the words "MaSoN wOrK". As one of dry pre-mixed products mentioned above, pre-mixed dry mortar (PMDM) has become an essential material in modern construction, offering significant improvements in quality, efficiency, and environmental sustainability. However, despite its advantages, quality issues can still arise during its use, often due to improper application or inherent challenges within the material itself. Common issues include plastic shrinkage cracking, drying shrinkage cracking, clumping and aggregation, non-compliance with test block strength, surface detachment and uneven finish, inconsistent setting time, water separation and surface foaming etc. Taking critical measures from proper curing, environmental control, continuous training and regular quality control can help to minimize quality issues.


Polymer cement mortar

Polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
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
latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latices are found in nature, but synthetic latices are common as well. In nature, latex is found as a wikt:milky, milky fluid, which is present in 10% of all floweri ...
es or
emulsions An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althoug ...
, redispersible polymer powders, water-soluble polymers, liquid thermoset resins and monomers. Although they increase cost of mortars when used as an additive, they enhance properties. Polymer mortar has low permeability that may be detrimental to moisture accumulation when used to repair a traditional brick, block or stone wall. It is mainly designed for repairing concrete structures. The use of recovered plastics in mortars is being researched and is gaining ground. Depolymerizing PET to use as a polymeric binder to enhance mortars is actively being studied.


Lime mortar

The setting speed can be increased by using impure limestone in the
kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or Chemical Changes, chemical changes. Kilns have been used for millennia to turn objects m ...
, to form a
hydraulic lime Hydraulic lime (HL) is a general term for a variety of lime different from calcium oxide (quicklime), that sets by hydration and consists of calcium silicate and calcium aluminate, compounds that can harden in contact with water. This contras ...
that will set on contact with water. Such a lime must be stored as a dry powder. Alternatively, a pozzolanic material such as calcined clay or brick dust may be added to the mortar mix. Addition of a pozzolanic material will make the mortar set reasonably quickly by reaction with the water. It would be problematic to use Portland cement mortars to repair older buildings originally constructed using lime mortar. Lime mortar is softer than cement mortar, allowing brickwork a certain degree of flexibility to adapt to shifting ground or other changing conditions. Cement mortar is harder and allows little flexibility. The contrast can cause brickwork to crack where the two mortars are present in a single wall. Lime mortar is considered breathable in that it will allow moisture to freely move through and evaporate from the surface. In old buildings with walls that shift over time, cracks can be found which allow rain water into the structure. The lime mortar allows this moisture to escape through
evaporation Evaporation is a type of vaporization that occurs on the Interface (chemistry), surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evapora ...
and keeps the wall dry. Re−pointing or rendering an old wall with cement mortar stops the evaporation and can cause problems associated with moisture behind the cement.


Pozzolanic mortar

Pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash (), is a natural siliceous or siliceous- aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reaction). In this reaction ...
is a fine, sandy
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
. It was originally discovered and dug at Pozzuoli, nearby
Mount Vesuvius Mount Vesuvius ( ) is a Somma volcano, somma–stratovolcano located on the Gulf of Naples in Campania, Italy, about east of Naples and a short distance from the shore. It is one of several volcanoes forming the Campanian volcanic arc. Vesuv ...
in Italy, and was subsequently mined at other sites, too. The Romans learned that pozzolana added to lime mortar allowed the lime to set relatively quickly and even under water.
Vitruvius Vitruvius ( ; ; –70 BC – after ) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work titled . As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissan ...
, the Roman architect, spoke of four types of pozzolana. It is found in all the volcanic areas of Italy in various colours: black, white, grey and red. Pozzolana has since become a generic term for any siliceous and/or aluminous additive to slaked lime to create hydraulic cement. Finely ground and mixed with lime it is a hydraulic cement, like Portland cement, and makes a strong mortar that will also set under water. The fact that the materials involved in the creation of pozzolana are found in abundance within certain territories make its use more common there, with areas inside of
Central Europe Central Europe is a geographical region of Europe between Eastern Europe, Eastern, Southern Europe, Southern, Western Europe, Western and Northern Europe, Northern Europe. Central Europe is known for its cultural diversity; however, countries in ...
as well as inside of
Southern Europe Southern Europe is also known as Mediterranean Europe, as its geography is marked by the Mediterranean Sea. Definitions of southern Europe include some or all of these countries and regions: Albania, Andorra, Bosnia and Herzegovina, Bulgaria, C ...
being an example (significantly because of the many European volcanoes of note). It has, as such, been commonly associated with a variety of large structures constructed by the
Roman Empire The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of ...
.


Radiocarbon dating

As the mortar hardens, the current atmosphere is encased in the mortar and thus provides a sample for analysis. Various factors affect the sample and raise the margin of error for the analysis. Radiocarbon dating of mortar began as early as the 1960s, soon after the method was established (Delibrias and Labeyrie 1964; Stuiver and Smith 1965; Folk and Valastro 1976). The very first data were provided by van Strydonck et al. (1983), Heinemeier et al.(1997) and Ringbom and Remmer (1995). Methodological aspects were further developed by different groups (an international team headed by Åbo Akademi University, and teams from CIRCE, CIRCe, ETHZ, Poznań, RICH and Milano-Bicocca laboratory. To evaluate the different anthropogenic carbon extraction methods for radiocarbon dating as well as to compare the different dating methods, i.e. radiocarbon and OSL, the first intercomparison study (MODIS) was set up and published in 2017.


See also

* Cement accelerator *
Concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
* Energetically modified cement * Grout * Thick bed mortar (technique) * Thinset * Tuckpointing


References


Concrete blowouts in Post-tension slabs
*Technical data sheets, Mortar Industry Association, www.mortar.org.uk {{Authority control Masonry Bricks Cement Concrete Soil-based building materials