Mortar (masonry)
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[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. The first evidence of the use of lime to bind stones is deemed to be a concrete floor in Yiftah El, Galilee, Israel about 7000 BC.[1]In early Egyptian pyramids that were constructed 2600-2500 B.C., the limestone blocks were bound by mortar of mud and clay, or clay and sand.[2] In pyramids built in later Egyptian dynasties, the mortar was made of either gypsum or lime.[3]Gypsum mortar was essentially a mixture of plaster and sand and was quite soft.Tvbanfield (talk) 23:02, 3 January 2008 (UTC)
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.[4] Pozzolanic mortar is a lime based mortar, however it is made with an additive of volcanic ash that allows it to be hardened under water, 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.[ http://www.hcia.gr/3a.html]Tvbanfield (talk) 18:50, 4 January 2008 (UTC)
[edit] Portland cement mortar
Portland cement mortar (often known simply as cement mortar) is created by mixing Portland cement with sand and water.
It was invented in the mid-nineteenth century, as part of scientific efforts to develop stronger mortars than existed at the time. It was popularized during the late nineteenth century, and by 1930 it had superseded lime mortar for new construction. The main reason for this was that it sets hard and quickly, allowing a faster pace of construction. 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 gravel.
[edit] Lime mortar
Lime mortar is created by mixing sand, slaked lime and water.
The earliest known use of lime mortar dates to about 4000 BC in Ancient Egypt. Lime mortars have been used throughout the world, notably in Roman Empire buildings throughout Europe and Africa. The vast majority of pre-1900 masonry buildings in Europe and Asia are built from lime mortar.
The process of making lime mortar is simple. Limestone is burnt in a kiln to form quicklime. The quicklime is then slaked (mixed with water) to form slaked lime, either in the form of lime putty or of hydrated lime powder. This is then mixed with sand and water to form mortar.
This kind of lime mortar, known as non-hydraulic, sets very slowly through reaction with the carbon dioxide in air. A very thick wall made of lime mortar may take centuries to completely set and harden. This is normal and not problematic.
The speed of set can be increased by using impure limestones in the kiln, to form a hydraulic lime 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. This will have a similar effect of making the mortar set reasonably quickly by reaction with the water in the mortar.
Using Portland cement mortars in repairs to older buildings originally constructed using lime mortar can be problematic. This is because lime mortar is softer than cement mortar, allowing brickwork a certain degree of flexibility to move to adapt to shifting ground or other changing conditions. Cement mortar is harder and allows less 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 it and evaporate from its surface. In old buildings with walls that shift over time, there are often cracks which allow rain water into the structure. The lime mortar allows this moisture to escape through evaporation and keeps the wall dry. A common mistake of repointing or rendering an old wall with cement mortar stops this evaporation and can cause damp problems behind the cement.
[edit] Pozzolana mortar
Pozzolana is a fine, sandy volcanic ash, originally discovered and dug in Italy at Pozzuoli in the region around Mount Vesuvius, but later at a number of other sites. The ancient Roman architect Vitruvius speaks of four types of pozzolana. It is found in all the volcanic areas of Italy in various colours: black, white, grey and red.
Finely ground and mixed with lime it acts like Portland cement and makes a strong mortar that will also set under water.
[edit] See also
[edit] References
cs:Malta (stavebnictví)da:Mørtel de:Mörtel es:Mortero (construcción) fr:Mortier (matériau) gd:Aol-tàthaidh hr:Vapno it:Malta (materiale) he:מלט nl:Mortel ja:モルタル no:Mørtel pl:Zaprawa murarska sr:Креч fi:Laasti sv:Murbruk pt:Argamassa
