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Mortar is a workable paste formed by mixture of cement, water and fine aggregate masonry to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, breeze blocks (cinder blocks), etc. Mortar is a mixture of sand, a binder such as cement or lime, and water and is applied as a paste which then sets hard. Mortar can also be used to fix, or point masonry when the original mortar has washed away.[1]

[edit] Ancient mortar

The first mortars were made of mud and clay. Because of a lack of stone and an abundance of clay, the Babylonian constructions were of baked brick, using slime or pitch for mortar. According to Roman Ghirshman, the first evidence of man using a form of mortar was at the ziggurat of Sialk in Iran, built of sun-dried bricks in 2900 BC.[2] The Chogha Zanbil Temple in Iran was built in about 1250 BC with kiln-fired bricks and a strong mortar of bitumen.

In early Egyptian pyramids constructed about 2600-2500 B.C., 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.

Historically, building skills with concrete and mortar next appeared in Greece. 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.[5] Pozzolanic mortar is a lime based mortar, however it is made with an additive of volcanic ash that allows it to be hardened underwater, thus 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.[4] Even later, the Romans used a mortar without pozzolana using crushed terra cotta, which introduced aluminum oxide and silicon dioxide into the mix. This mortar was not as strong as pozzolanic mortar, but, because it was denser, it better resisted penetration by water.[6]

It is not understood why 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 when the gothic cathedrals were being built, the only active ingredient in the mortar was lime. Since cured lime mortar could be degraded by contact with water, many structures suffered from wind blown rain over the centuries.

[edit] Portland cement mortar

Portland cement mortar (often known simply as cement mortar, or OPC) is created by mixing Portland cement with sand and water.

It was invented in 1794 by Joseph Aspdin and patented on 18 December 1824, largely as a result of various scientific efforts to develop stronger mortars than existed at the time. It was popularized during the late nineteenth century, and, thanks to the first World War, by 1930 it had superseded lime mortar for new construction. The main reasons for this was that it sets hard and quickly, allowing a faster pace of construction, and required less skilled workers. However, as a general rule, it should not be used for the repair of older buildings constructed in lime mortar, which require the flexibility, softness and breathability of lime if they are to function correctly.

The Portland cement mortar is the basis for concrete, a mixture usually composed of this particular mortar with the addition of aggregate.

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