What is Lime?

Lime chemical terminology explained - click here
Building lime terminology explained - click here
Other chemical & misc. terminology explained - click here

Lime is made from calcium carbonate. This can be found in a variety of forms for example chalk, limestone or sea shells. In the British Isles sources are almost invariably chalk or limestone. In the case of Singleton Birch, it is mainly chalk quarried in Lincolnshire.

To convert the raw material into lime, heating to temperatures between 800 C - 1000 C is required. At these temperatures the chalk breaks down by giving off carbon dioxide leaving calcium oxide which is known as quicklime.

Quicklime is unstable and reacts, often very rapidly, with water to form calcium hydroxide. This process produces heat and is known as hydration. When exposed to the atmosphere this calcium hydroxide can react again by absorbing carbon dioxide from the atmosphere to once again become calcium carbonate.

This is known as the lime cycle and is shown in the diagram below.

It is calcium hydroxide which, when mixed with sand to make a mortar, builders have used over the millennia. The setting process is the re-absorption of carbon dioxide from the atmosphere called carbonation.

Calcium hydroxide can be used by Builders in two forms, firstly, if it is hydrated with an excess of water, lime putty is produced or if the water quantity is reduced a powder is formed which can be bagged.

All sources of pure calcium carbonate produce a similar result, however the Romans discovered that the calcium hydroxide would also react with volcanic ash, essentially a mixture of silica and alumina. The resulting mixes set very much harder and for the first time enabled structures of high strength to be built. By varying the quantity of silica and alumina, mortars (and lime concretes) of different strengths could be produced. These reactions are referred to as pozzolanic, from the town of Pozzuoli in Italy from where the original material came.
The processes described so far use chalk or limestone that is relatively pure containing over 95% calcium carbonate. However some limestones are less pure and can contain quantities of silica and alumina which when heated produce very similar results to the Roman mixes of pure lime with volcanic ash. These impure limestones if they contain quantities of silica and alumina are referred to as Natural Hydraulic Limes (NHL).

Hydraulic in this context refers to the ability of the material to set under water as opposed to pure air limes which can only set when exposed to atmospheric carbon dioxide. As with addition of pozzolanic silica and alumina, the strength of NHL's depends upon the quality of these materials in the limestone. As the quantities increase so does the strength but also the free lime (calcium hydroxide) in the mortar reduces so that the set depends more on chemical reaction and the process of carbonation reduces.

Singleton Birch have worked to develop a range of NHL products by sourcing the appropriate chalk or limestone for burning, based on its' geology and mineralogy.
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Lime terminology
calcium carbonate
also known as: chalk, limestone, agricultural lime
chemical formula: CaCO3

calcium oxide
also known as: quicklime, burnt lime
chemical formula: CaO

calcium hydroxide
also known as: hydrated lime, slaked lime
chemical formula: Ca(OH)2
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Building Lime terminology
Air lime
Air lime, or high calcium lime does not have any hydraulic component. It can be quicklime for slaking or hydrated lime. It gains strength slowly, by combining with atmospheric carbon dioxide to form calcium carbonate (as per the lime cycle). Several grades of air lime are identified in EN459 the European standard for Building Lime.

Hydraulic lime
Lime with hydraulic or cementitious properties which will set when exposed to moisture. Several grades of hydraulic lime are identified in EN459 the European standard for Building Lime.

Natural hydraulic lime
Hydraulic lime which does not contain any performance enhancing additives. Its properties are as a result of the mineralogy of the calcium carbonate stone which is quarried for burning.

Hydrated lime
Hydrated lime is NOT hydraulic lime and will not set in contact with water.

CL90 & CL90 S
Grades of air lime for building as described in EN459 the European standard for Building Lime. CL90 is the purest grade of building quicklime and CL90 S is the purest grade of hydrated lime for building. Several grades of air lime are identified in EN459 the European standard for Building Lime.

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Other chemical & misc. terminology
carbon dioxide
chemical formula: CO2

water
chemical formula: H20

silica
chemical formula: Si02

alumina
chemical formula: Al203


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Lime Mineral Data

Help on Chemical Formula: Chemical Formula: CaO
Help on Composition: Composition: Molecular Weight = 56.08 gm
Calcium 71.47 % Ca 100.00 % CaO
Oxygen 28.53 % O
______ ______
100.00 % 100.00 % = TOTAL OXIDE
Help on Empirical Formula: Empirical Formula: CaO
Help on Environment: Environment: Thermally metamorphosed calcareous ejecta.
Help on IMA Status: IMA Status: Valid Species (Pre-IMA) 1935
Help on Locality: Locality: Vesuvius, Campania, Italy Link to MinDat.org Location Data.
Help on Name Origin: Name Origin: Named from the Old English, quicklime.
Help on Name Pronunciation: Name Pronunciation: Lime Say LIME
Help on Synonym: Synonym: Calcium Oxide
Chaux
ICSD 75785
PDF 37-1497

Quicklime or Calcium Oxide

Inorganic compound, white or grayish white solid, chemical formula CaO, made by roasting limestone (calcium carbonate, CaCO3) until all the carbon dioxide (CO2) is driven off. One of the four most important basic chemical commodities, it is used as a refractory, as a flux in steel manufacture, as a CO2 absorbent, to remove contaminants from stack gases, to neutralize various acids, in pulp and paper, in insecticides and fungicides, in sewage treatment, and in the manufacture of glass, calcium carbide, and sodium carbonate. Adding water to lime yields calcium hydroxide (slaked lime, calcium hydrate, hydrated lime, or caustic lime), which is used in mortar, plasters, cements, whitewash, hide dehairing, and water softening and purification and as a source of other calcium salts.

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calcium oxide

calcium oxide, chemical compound, CaO, a colorless, cubic crystalline or white amorphous substance. It is also called lime, quicklime, or caustic lime, but commercial lime often contains impurities, e.g., silica, iron, alumina, and magnesia. It is prepared by heating calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral.. (e.g., limestone limestone, sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine.in a special lime kiln to about 500°C; to 600°C;, decomposing it into the oxide and carbon dioxide. Calcium oxide is widely used in industry, e.g., in making porcelain and glass; in purifying sugar; in preparing bleaching powder bleaching powder, white or nearly white powder that is usually a mixture of calcium chloride hypochlorite, CaCl(OCl); calcium hypochlorite, Ca(OCl)2; and calcium chloride, CaCl2. , calcium carbide, and calcium cyanamide; in water softeners; and in mortars and cements. In agriculture it is used for treating acidic soils (liming liming (lim`ing), application to the soil of calcium in various forms, generally as ground limestone, but also as marl, chalk, . It is incandescent when heated to high temperatures; the Drummond light, or limelight, provides a brilliant white light by heating a cylinder of lime with the flame of an oxyhydrogen torch. Calcium oxide is a basic anhydride, reacting with water to form calcium hydroxide calcium hydroxide, Ca(OH)2, colorless crystal or white powder. It is prepared by reacting calcium oxide (lime) with water, a process called slaking, and is also known as hydrated lime or slaked lime. the link for more information. ; during the reaction (slaking) much heat is given off and the solid nearly doubles its volume.

Limestone

Limestone is a "chemical" sedimentary rock that is composed mostly of calcite (CaCO3) that precipitates from seawater. Limestone, the most common chemical sedimentary rock in Texas, is commonly white to gray. Because the dominant mineral is calcite, limestone reacts with a strong effervescence when tested using a dilute acid such as hydrochloric acid or vinegar. Groundwater is slightly acidic and, hence, slowly dissolves limestone. This process has produced the caves of Texas.

Variations of limestone include marl, a muddy limestone, and chalk, a limestone composed of microscopic calcareous algae and tiny shells of marine organisms. Limestone is common in the Hill Country and the Trans-Pecos of Texas. Limestone in Texas is quarried for cement, aggregate, and building stone. High-calcium-content limestone is used in water purification and sewage treatment.

The limestone sample in the Texas Rock Kit was collected in Travis County and is Cretaceous in age.