History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c29.s2.t4: Mortars and Plasters
History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c29.s2.t4
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Mortars and Plasters
v1.c29.s2.t4.1
Amongst the building materials mortars and plasters are important ingredients. mortar may be defined as a material used for building or cementing the building materials e.g. bricks or stones. Plaster is the material used for coating walls etc. Some times the same material may be used as a mortar as well as for plaster. In ancient period mud was almost exclusively used as mortar and plaster. Though gypsum and lime plaster/mortar have been used during antiquity. The earliest use of lime and gypsum comes from Indus civilization.
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At Harappa, gypsum cement of light grey colour was used in certain buildings. It consists of variable mixture of sand (20 to 40%), gypsum (45 to 75%) and lime (2 to 25%). Lime mortar with sizeable percentage of magnesium is also used in Indus Civilization. It contains calcium carbonate (26 to 57%), magnesium carbonate (4 to 11%) and sand clay (34 to 61%). The high percentage of sand and clay in lime plaster suggests that it was prepared by burning *Kankar* (calcarious nodules). The use of lime was restricted to drains and floors. *(See Table 1)*.
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From the analysis of various samples of mortars and plasters from Mohenjo-daro, it may be concluded that gypsum mortar/plaster was quite common. Lime plaster was generally mixed with gypsum, but lime plaster free from gypsum has also been reported both from Harappa and Mohenjo-daro. The use of lime and gypsum mortar was confined to drains or floors where mud mortar was of no use. Gypsum and lime mortar are stronger and resistant to water.
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Lime mortars have been used at Kausambi. These date from 600 B.C. to A.D. 100. But it may be emphasized that by and large only mud mortar and plaster were used. The results of the chemical analysis (*Tables 2* and *3*) show that the content of sand in the mortar, was slightly higher than that in plasters. The average ratio of sand : lime Ca(OH)₂ is about 1:1, whereas in the case of mortars the average is 2:1. For mortars, probably 2 parts of sand were mixed with one part of slaked lime.
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Lime Plaster from Karwan (Dt. Vadodara, Gujrat) from pre- Gupta levels : From the analysis (*Table 4*) it is clear that two types of plaster was used. Samples 1 to 4 represent the upper coat of the plaster and 5 to 8 represent lower rough plaster. The former has higher content of lime as compared to the latter. Fine layer was laid and burnished to make it smooth and elegant.
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Lime Plaster from Bhitari (Dt. Gazipur. U.P) (Gupta Period) : shows low grade lime plaster (*Table 5*) was used at the brick temple of Gupta period. It has sand and lime ratio of 6:1. The red colour of the plaster/mortar is due to the use of ferruginous *kankar* for preparation of lime.
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Lime Plaster from excavations at Nalanda (7th-10th century A.D) (*Table 6*) shows 3 parts of lime (calcium carbonate) and 2 parts of sand. Some of the monasteries are thickly plastered. Jars with dried up mortar and a cell used as a cistern in monastery No 11 are indicative of the preparation of concrete.
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Lime Plaster from Lingaraj temple at Bhubhaneshwar (Orissa - 10th century A.D) (Table 7) shows that lime:silica ratio was 3:1.
v1.c29.s2.t4.9
Cola and Nayaka Plasters show two types of plasters used : rough and fine, it has a ratio of 1:1 of lime : sand in rough plaster, and 9:1 in case of fine plaster. Nayaka rough plaster 1:3 lime : sand ratio, while fine plaster has 4:1 ratio.
v1.c29.s2.t4.10
Lumps of finely made lime in the shape of balls have been found mostly from late Jorwe levels at Inamgaon (datable to first millenium B.C.). Sometimes these have been carefully stored in pots. In one house of late Jorwe phase a large number of lime balls were found. This indicates some people were engaged in the manufacture of lime. Significantly a heap of shell, was noticed near the house, but no kiln.
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Lime kiln for manufacturing Lime : Kilns were rudely constructed of stone blocks and usually located in a cavity. In charging the kiln large pieces of limestones were formed into a dome like arch with large open joints and kiln was filled with fragments of lime stones. The larger pieces of lime stone were placed above the arch and kiln was topped with fragments of small size. Kiln was charged with alternate layer of lime stone and fuel (wood). Bright heat was maintained for three or four days at a temperature of about 95°C, lime stone, kankar modules, sea shells are converted into quick lime (CaO) and CO2 gas is evolved. Before using it is slaked by mixing it with mater and slaked lime is mixed with sand or bajari for masonry work.
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In addition to the above, mention may be made of use of clay, lime, gravel and hydraulic lime from post-chalcolithic levels at Navasa.
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At Taxila, lime is used extensively during Parthian levels. Though at Bhir mound there is no evidence of the use of lime plaster. At Sirkap lime was used for finishing both internal and external surfaces. Floors at Julian (Takile) were covered with bajari-lime concrete.
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At Arikamedu lime mortar is reported from historical period. Use of lime is also attested from Hullas Khera (Dt. Lucknow) from Kuṣāṇ-Gupta levels and from Banagarh (Dt. Dinajpur) where use of lime and Surkhi is known from Gupta and Pala levels. At Purana Quila lime plastered gutter connected with house drains is reported from levels datable to 8th-9th century A.D.