Lime Concrete Terracing

Lesson 19 : Roof And Roof Coverings

Types Of Flat Roofs

Lime Concrete Terracing

This type of terracing is commonly used over flag stone roofing, though it can also be used R.C.C slab. The procedure of lime terracing varies from place to place. The one adopted for Jodhpur stone slab roofing is described below, is steps:

  1. The longitudinal joints between the stone slabs are first pointed in cement mortar. The joints should be negative shaped, not exceeding 25 mm at the top and 10mm at the bottom. This joint is filled with cement mortar (mix 1:2 to 1:4) and picked with stone chips of wedge shape and top finish rounded with cement mortar so as to project little above the slabs. Before filling mortar in the joints, flat strips of timber (or 3 inch dia. bamboos) should be kept along the joint on the other face of the stone slabs so that mortar does not fall down. Similarly, the space left over the walls at the ends of the slabs and also the space on walls between the slabs where roof is continuous should be filled with 1:2:4 cement concrete. These joints should be properly cured, at least for 7 days.

  2. In order to provide proper slope to the roof, ralthal is laid. This is done by laying stone spawls in 1:2 line mortars over the surface of the slabs in the required thickness. Hydraulic lime (kankar lime) should be used. Ralthal so laid should be cured for 7 days.

  3. Laying of the lime chhat is done in four consecutive days. On the first day, unslaked Kankar lime (hydraulic lime) 10 cm in thickness is spread over the roof slabs. The lime is then slaked in situ, by adding water. It is then beaten with conical stone so that no particles of lime remain unslaked to cause blisters.

  4. On the second day, the lime is watered, raked up and again the process of first day is repeated.

  5. On the third day, 250 gm of hemp (finely chopped) and methi 750 gm finely powdered per 10 sq metres is evenly and thoroughly mixed with the lime. Then coarse stone aggregate duly washed should be spread over this lime in a thickness not less than 10 cm.

  6. On the fourth day, stone grit or screening is spread in a layer of 40 mm and beaten with stone beaters till they are well set. This process of beating should continue with wooden thapies and by sprinkling water till the whole mass becomes stiff and offers resistance to penetration. Thickness of lime chhat should not be less than 15 cm at any place.

  7. The above work should be cured at least for 7 days.

  8. After seven days, sandal coat consisting of cream of lime is laid over the lime chat in thin layers and rubbed for full four hours or more , using rounded pebbles for rubbing and polishing. During the process of rubbing, solution of 65 gm of Gur and 250 gm of Gugal per 10 square meters is sprinkled every now and then.

  9. The surface thus prepared is cured with water at least for 15 days using damp sand or moist gunny bags so as to keep the surface constantly wet.
Last modified: Saturday, 21 April 2012, 6:17 AM