bitumen mastic for use in water-proofing of roofs
1992 Edition

IS 3036 specifies the use of slaked lime as the primary binder. Pozzolanic materials include burnt brick pozzolana mixed with lime in a 2:1 volume ratio, lime-pozzolana blends conforming to LP 40 grade under IS 4098, and calcined clay pozzolana as per IS 1344. The mortar mix typically consists of one part slaked lime to two parts burnt brick pozzolana by volume, ground with water, combined with 2.5 parts saturated surface dry coarse aggregates to form durable, waterproof lime concrete.

For effective waterproofing, mix 2.5 parts saturated surface dry coarse aggregate with 1 part lime by volume, adding pozzolanic mortar such as burnt brick pozzolana. Thoroughly blend the components to ensure uniformity, adjusting water content for workability. Compact the mix manually by hand-beating, simultaneously sprinkling lime water diluted at 1 part lime putty to 3–4 parts water. Adding sugar or Terminalia chebula (Kadukai) solutions during compaction enhances water resistance. Smooth the surface with a trowel using lime putty and sugar solution. If water pockets form, prick the surface, add fresh lime concrete, compact again, and sprinkle lime water to maintain bonding and slope.

The standard recommends a minimum slope of 1 in 60 (approximately 1.67%) for flat roofs to ensure adequate drainage. In regions experiencing heavy rainfall, increasing the slope to 1 in 40 (2.5%) is advised for improved runoff. For terrace finishes, lime concrete with tile coverings should maintain at least a 1 in 60 slope, while plain lime concrete finishes require a minimum slope of 1 in 50 (2%). The lime concrete layer thickness should be no less than 100 mm, with individual layers ranging from 100 to 125 mm, ensuring effective drainage and protection against water accumulation.

At the junction of the roof and parapet walls, a smooth lime concrete fillet strip is laid continuously to prevent water ingress, as per Clause 7.5 of IS 3036. The concrete at this junction must be properly consolidated to avoid voids and enhance durability. A 12 mm wide gap partially filled with bitumen filler accommodates structural movement. The lime concrete roof finish is laid with a minimum slope of 1 in 50 towards drainage outlets. Additional features include a 20 mm deep plaster drip course to deflect water and rainwater pipes installed at a rate of one 100 mm diameter pipe per 40 m² of roof area to facilitate drainage.

Curing of lime concrete requires a minimum period of 10 days or until the material attains sufficient hardness. The curing method involves covering the compacted lime concrete with a thin layer of grass or straw that is kept continuously moist. During compaction, the surface should be sprinkled liberally with lime water prepared by mixing 1 part lime putty with 3 to 4 parts water. Incorporating sugar or Terminalia chebula (Kadukai) solutions during this stage enhances waterproofing by increasing surface hardness and water repellency. Pozzolanic additives like burnt brick pozzolana further improve the density and durability of the waterproof finish.