Waterproofing of Flat Roofs

The flat roof should be made waterproof by a surface covering. The following methods are employed:

1. Cement mortar finishing
2. Bedding concrete and flooring
3. Mastic asphalt
4. Waterproofing compounds

1. Cement Mortar Finishing

For small buildings or normal use, the finishing of roof surface is done at the time of laying cement concrete. The flat roof is finished with cement mortar of 1 : 4.

2. Bedding Concrete and Flooring

The concrete surface is kept rough over which a brick bats lime concrete of 1 : 2 : 4 or brick bats cement concrete of 1 : 18 : 24 is laid for a thickness of about 10 cm. The bedding concrete is finished with tiles, stone slabs or terrazzo, etc. A convex joint is provided at the junction of parapet wall and the roof.

3. Mastic Asphalt Finish

A layer of hot mastic asphalt is laid on the roof surface and a jute cloth is spread over this surface. One more layer of mastic asphalt is laid over the jute cloth such that the jute cloth is sandwiched between to asphalt layers. Then sand is sprinkled over the entire surface of the roof. A led sheet is inserted at the junction of the parapet and the roof so as to have a better grip and easy draining.