TAN 1 : Building Lime
Building lime has been used for building construction in India from ancient times. Advent of Islamic architecture brought about extensive use of hydraulic lime, which served not merely as binding medium, but also as plaster and base incised decoration and encaustic enamel work.* Buildings constructed with lime have survived natural calamities and continuous weathering for more than a millennium throughout India are physical evidences of the longevity and the durability of the traditional knowledge about the material.
It was used for architectural, structural and decorative purpose as well as in different challenging situations. The fine plaster work in India depended for its finish and durability on arduous and time consuming labour working with wooden mallet whilst setting took place.
Lime and lime products have been used from a very early period in the history of civilization. The earliest traces of the use of lime in constructional work are of lime plaster and stucco in India and in early Egyptian and Roman buildings. Some of these dates around 2300 BC.
In India, building lime is produced by burning calcium rocks, such as chalk, lime stone, dolomite and marl bearing limestone, dolomite and marl bearing chalk, oyster shell (seep), conch (sankh) etc. A particular limestone would be suitable raw material for producing lime only if it has suitable composition in its raw material.
Non Hydraulic lime or lime rich, less than 10% clay impurities
Hydraulic lime, 10-30% clay and 60-40% lime
Cement, 40-60% clay and 60-40% lime
The characteristics of limestone vary according to impurities it contains and these impurities give rise to variety of types of lime of varying nature and quality. The characteristics of building lime depend upon the key elements such as the composition of limestone, firing temperature, duration of firing and the firing technique. Building limes were classified by French engg. L.J. Vicat in the early 19th century as described in the table below:
Type of lime vs resource lime composition**
Indian Standard Institution has adopted several standards on the lime for civil work due to the long felt need for uniformity in the variety of practices being followed in the manufacturing and use of lime in construction work. Building limes shall be classified as follows***:
Class A - Eminently hydraulic lime used for structural purposes.
Class B - Semi-hydraulic lime used for masonry mortars, lime concrete and plaster undercoat.
Class C - Fatlime used for finishing coat in plastering, whitewashing, composite mortars, etc, and with addition of pozzolanie materials for masonry mortar.
Class D - Magnesium/dolomitic lime used for finishing coat in plastering, white washing, etc.
Class E – Kankar lime used for masonry mortars.
Class F - Siliceous dolomitic lime used for undercoat and finishing coat of plaster.
NOTE 1 - Lime shall be available either in hydrated or quick form, except that of Classes A and E which shall only be supplied in hydrated form.
NOTE 2 - Applications indicated are only suggestive.
The building lime is procured from burning the limestone. The two important factors played important role for the quality of lime produced:
· Temperature and the duration of the kiln firing, which gives different compositions at different temperatures and cooling rate.
· Mineral composition of the limestone is the important factor. Traditional belief was that “lime prepared from the hardest limestone and preferably from the moist, shady quarries should produce hard mortars. In contrast soft stones such as chalk should only produce soft mortars”.
Pure limestone will produce non hydraulic lime, which does not set under water. Impure lime stone will produce hydraulic lime, which sets under water (Hydraulic means capacity to set under water)
Calcination is an endothermic reaction usually take place at or above the thermal decomposition temperature. In case of limestone calcination, a decomposition process, the chemical reaction for decomposition of the limestone is
CaCO3= CaO (quicklime) + CO2
The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it will be completely converted back to calcium carbonate unless slaked with water.
· Carbonation process starts immediately after calcination due to high reactivity of lime
· Method of transportation and weather considerations
· Storage in dry rooms in air tight bags
Packing and Storing
The hydrated lime shall be supplied, in suitable containers, such as jute bags lined with polythene or high density polythene woven bags lined with polythene or craft paper bags, preferably containing 50 kg of lime.
The quicklime shall be supplied in suitable containers preferably containing 50 kg of lime.
The lime packages shall bear the type and class of lime, the brand name of manufacturer, date of manufacture and the net weight; in case of quicklime the slaking temperature shall be indicated.
The lime shall be stored in such a manner as to permit easy access for proper inspection and in a suitable building to protect the lime from the dampness and to minimize warehouse deterioration.
To begin working with building lime it would be essential to know about the present availability of lime resources and the existing traditional practices with lime in India.
* Archaeological remains monuments and museum, Part-II, Archaeological Survey of India publication
**Holmes Stafford, Wingare Michael, (1997) Building with lime, a practical introduction, intermediate technology publications
***IS 712 (1984): Specification for building limes