Damp Proof Course – Damp Proofing
Damp Proof Course
One of the following specifications may be adopted for a damp proof course, according to the type of the construction and the nature of the ground:
(j) Two courses of dense bricks in 1. : 3 cement mortar. Bricks should have a water absorption of not more than 4.5 per cent. It is advantageous to leave the vertical joints unfilled as moisture rises through the mortar joints.
(ii) A layer of well burnt bricks soaked in hot tar and pitch will suit for cheap class buildings.
(iii) Non-porous stone slabs about 50 mm thick laid for the full width of the walls over a bed of cement mortar.
(iii) Two layers of non-porous slates laid to break joint, each layer being bedded and set solidly in cement mortar 1: 3.
(iv) 12 mm cement plaster 1 : 2 with some water proofing compound laid above the plinth masonry with one or two thick coats of hot coal tar applied over the mortar after the mortar has fully dried. Dry sharp sand should be sprinkled over the hot tar. Five per cent of Pudlo by weight of cement can be used for water proofing the mortar. .
(v) For 40 to 50 mm cement concrete 1 : 2 : 4. Two coats of asphalt or hot coal tar should be applied over the cement concrete when the concrete has been fully cured and dried. A coat of 7 asphalt mixed with 3 parts of clean sharp sand may be laid 6 min thick over the concrete. A layer of tough asphalt about 10 mm thick is often used instead of hot asphalt, Mastic asphalt in one or two layers is generally considered best where hydraulic pressure is encountered. The asphalt used should not melt or soften in the hottest days and should not get squeezed out due to pressure of the masonry over it.
The damp proof course should be laid flush with the floor surface and should not be carried across doorways or other openings. The upper layer of cement concrete floors should be continued over such openings and should be laid at the same time as the floors. The asphalt or tar layer should be laid under the concrete at the Openings. Where concrete is laid on bitumen or tar, the surface of the bitumen or tar must be sprinkled with dry sand.
The position of the damp proof course is also an important factor and it should be laid at such a height that it is above the normal level to which water splashes from the ground when it is raining. A damp proof course should not be less than 15 cm above the highest level of the ground. In Northern India plinths are usually kept 45 to 60 cm above ground level for good class buildings under normal conditions.