Mortar

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

mortar becomes hard when it cures, resulting in a rigid 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, a binder, and water. The most common binder since the early 20th century is but the ancient binder  is still used in some new construction. Lime and gypsum in the form of are used particularly in the repair and  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
The first mortars were made of mud and. Because of a lack of stone and an abundance of clay, n constructions were of baked brick, using lime or for mortar. According to, the first evidence of humans using a form of mortar was at the of  in the Indus Valley, Pakistan, built of  in 6500 BCE. The ancient sites of of third millennium BCE are built with kiln-fired bricks and a  mortar. Gypsum mortar, also called plaster of Paris, was used in the construction of the and many other 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 early Egyptian pyramids, which were constructed during the (~2600–2500 BCE), the limestone blocks were bound by mortar of mud and clay, or clay and sand. In later Egyptian pyramids, the mortar was made of either or lime. Gypsum mortar was essentially a mixture of and  and was quite soft.

In the, multiple cement types have been observed in the sites of the , such as the city-settlement that dates to earlier than 2600 BCE. 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 at Mohenjo-daro.

Historically, building with and mortar next appeared in. The excavation of the underground aqueduct of Megara revealed that a reservoir was coated with a ic mortar 12 mm thick. This aqueduct dates back to c. 500 BCE. 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 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 a using crushed, introducing and  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 to make an inorganic−organic composite  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 when the Gothic cathedrals were being built, the only active ingredient in the mortar was lime. Since cured can be degraded by contact with water, many structures suffered from wind blown rain over the centuries.

Ordinary Portland cement mortar
Ordinary Portland cement mortar, commonly known as OPC mortar or just cement mortar, is created by mixing powdered, 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  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 ratio of cement, lime, and sand used in mortar. The ingredients and the mix ratio for each type of mortars are specified under the 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. These type letters are apparently taken from the alternate letters of the words "MaSoN wOrK".

Polymer cement mortar
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 es or, 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. One brand of PCM is MagneLine.

Lime mortar
The setting speed can be increased by using impure limestone in the, to form a that will set on contact with water. Such a lime must be stored as a dry powder. Alternatively, a ic 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 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 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
is a fine, sandy. It was originally discovered and dug at, nearby 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. , 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.

Firestop mortar
mortars are mortars most typically used to large openings in walls and floors required to have a. They are items. Firestop mortars differ in formula and properties from most other cementitious substances and cannot be substituted with generic mortars without violating the.

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 or. It is sometimes pigmented to distinguish it from generic materials in an effort to prevent unlawful substitution and to enable verification of the.

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,,. The possibility to use radiocarbon dating as a tool for mortar dating was introduced 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). Than the methodological aspect were developed by different groups (an international team headed by, 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.