To produce building lime, limestone is heated to at least 900 o C to liberate carbon dioxide and produce quicklime (calcium oxide, Ca O).
The quicklime is then slaked with water to form calcium hydroxide (Ca(OH)2) or building lime, which is mixed with aggregates or filler (sand) and water to form mortar.
In its broadest sense mortar includes pitch, asphalt, and soft mud or clay, such as used between mud bricks. 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.However this is fraught with difficulty; the mortar may contain old limestone, either as remains from incomplete conversion into calcium oxide in the burning process or from sedimentary carbonate in the aggregate, yielding apparent ages that are too old due to this form of contamination.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.They have successfully completed a study of dating mortar in medieval churches in Finland using accelerator mass spectrometry radiocarbon dating of non-hydraulic mortar.
Atmospheric carbon dioxide is fixed in the carbonate formed during the hardening of lime mortar at the time of construction, which in principle makes it ideally suited for 14C dating.
It is then mixed with water and an aggregate (usually sand, gravel or volcanic pyroclastic materials) to form mortar.
When the mortar hardens it absorbs carbon dioxide from the atmosphere and forms calcium carbonate.
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.
The process of making mortar Mortar is an inorganic material, but the principle behind 14C-dating of mortar is the same as in 14C-dating of organic materials.