1. With Tarfelt ( Bitumen Felt)
A coat of hot bitumen is laid at the rate of 1.2kg/sqm (min) over a prepared smooth roof surface and Tarfelt is laid immediately, over which another coat of hot bitumen is applied. While the bitumen is still hot the roof is then covered with coarse sand, grit, gravel or tiles or any conventional roof surfacing.
For normal works, one layer of Tarfelt and two coats of hot bitumen are required and for heavy works, two layers of Tarfelt and three coats of hot bitumen are needed. The bitumen is heated to 170 deg. C. – 180 deg. C.
2. Using Polyethylene Film
i) Under Mud Pushta
A coat of ho bitumen at the rate 1.2kg./sqm (min) is laid over a prepared smooth roof surface. Polyethylene film of 100 to 150 mic. Thickness is laid over the warm tack coat of bitumen. An 80 to 150 mm layer of mud pushta is laid over the film.
Prior to the actual water-proofing treatment, the roof surface is prepared smooth, dust and dirt are removed and a coat of primer is applied to bind the residual dust.
ii) A modified method involves the use of polyethylene film/kraft paper laminate. The kraft paper provides the necessary rigidity to the film, making it possible to lay the film free of wrinkles.
Hot bitumen is applied at the min rate of 1.2 kg./sqm. The polyethylene film/paper laminate with the film face downwards is applied and pressed down over the warm tacky coat of bitumen. The overlap joints of min width 75mm are sealed with the help of hot bitumen. Hot bitumen is mopped over the paper surface of the laminate at the min rate of 2.5 kg./sqm. Over the roofing ties or any conventional roofing material is applied.