Code of practice for laying damp-proofing treatment using bitumen felts
1991 Edition

Recommended bitumen felts for damp-proofing according to the standard include Hessian base self-finished felt Type 3, Grade 2, and glass fibre base felt Type 2, Grade II. Hot applied blown bitumen is used at a rate of 1.5 kg/m² between each felt layer. Typically, one felt layer is suitable for structures with a lifespan up to 10 years, while two layers are preferred for longer durations. Treatments are categorized as normal (two layers), heavy (three layers), and extra heavy (four layers), with appropriate primer application on vertical surfaces. Fibre-based felts are discouraged for basement waterproofing. Proper overlapping and hot bitumen bonding of joints are essential to achieve durability.

Site preparation should ensure the area is free from water by continuous pumping until damp-proofing is completed and structural protection is in place. The surface must be thoroughly dried using appropriate methods to promote adhesion of bitumen. In cases where the surface remains damp, the initial hot bitumen coat might not adhere well, but adhesion is ensured by the felt layer and properly sealed overlaps. Walls must be kept dry, and a bituminous primer at 0.27 l/m² should be applied on vertical surfaces before bitumen application. Hot applied blown bitumen is used at 1.5 kg/m² per layer, with felt layers selected according to building lifespan requirements.

For basement and subterranean damp-proofing, the standard recommends multiple layers of bitumen felt. The normal treatment involves two felt layers separated by hot applied blown bitumen (1.5 kg/m²) with a primer applied on vertical faces at 0.27 l/m². The felt types specified are Hessian base self-finished felt Type 3, Grade 2 or glass fibre base felt Type 2, Grade II. Overlaps must be continuous and well bonded to create an impermeable barrier. Heavy and extra heavy treatments entail three or four felt layers respectively, with alternating bitumen applications. Fibre-based felt is not advised for below-ground use.

Materials conforming to the standard include bitumen primer adhering to IS 3384:1986 and blown bitumen bonding material as per IS 702:1988, preferably penetration grades 85/25 or 90/15. Surface preparation mortar consists of cement-sand mix (1:4) with Ordinary Portland Cement meeting IS 269:1989 and sand complying with IS 2116:1980, free from impurities. This sequence of surface preparation, primer application, and hot bitumen bonding ensures strong adhesion for placing bituminous felts, guaranteeing the durability of the damp-proofing treatment.

Overlap joints must be carefully constructed with a minimum width of 75 to 100 mm to prevent water ingress. These joints are bonded using hot applied blown bitumen at approximately 1.5 kg/m² between felt layers and at the overlapping sections. Each felt layer, whether Hessian base self-finished felt Type 3, Grade 2 or glass fibre base felt Type 2, Grade II, is bonded in this manner, with primer applied on vertical surfaces prior to bitumen application. This technique ensures a continuous, watertight damp-proof membrane as required by the standard.