How to make Water proof Cement Concrete
For certain types of works like water storage tanks, reservoirs, basement walls, roofs, swimming pools, sewage units, etc., the impermeability of concrete is absolutely essential. In general, it can be state that if concrete is make dense and free from cracks, it is watertight. The dense concrete can be obtain by closely adhering the following water proof cement concrete essentials :-
- Using a high class Portland cement of guaranteed quality.
- Taking extreme care to adopt correct grading and proportioning of the sand, aggregate and cement.
- Using clean and non-porous aggregates.
- Mixing thoroughly to the right consistency using the right amount of water.
- Placing, tamping and curing carefully.
- Making use of suitable water-proofing compound.
The cement concrete to a certain extent may be make impermeable to the water by using hydrophobic cement. All the flat roofs in the modern age are generally construct of R.C.C. It becomes necessary to give some treatment of water-proofing to such roofs.
Following are the four methods adopt for water-proofing of R.C.C. flat roofs :
For ordinary buildings of cheap construction, the finishing of roof surface is done at the time of laying cement concrete. The finishing of flat roof is carry out in cement mortar of proportion 1 : 4 i.e., one part of cement to four parts of sand by volume.
Bedding concrete and flooring
In this method, the surface of R.C.C. slab is keep rough and on this surface, a layer of concrete is lay. The concrete may be brickbats line concrete ( 1 : 2 : 4 ) on brickbats cement concrete ( 1 : 6 : 12 ). The thickness of the concrete layer is about 100 mm. The surface of the bedding concrete is provide by a suitable flooring such as tiles, terrazzo, Indian patent stone, etc. A convex joint is provide at the junction of parapet wall and roof.
Mastic asphalt and jute cloth
In this method, a layer of hot mastic asphalt is lay on the roof surface. The jute cloth is spread over this layer. Then one more layer of mastic asphalt is apply so that the jute cloth is sandwich between the two layers of mastic asphalt. The sand is then sprinkle over the entire surface of roof. For better grip, the lead sheets are insert at the junction of parapet wall and roof.
Use of water-proofing compounds
Some of the water-proofing compounds like pudlo, Impermo, etc., are available in the market and when such a compound is add to the cement during construction, it prevents seepage, leakage and damp cause by the capillary absorption of the moisture in cement, mortar and concrete. The quantity of water-proofing compound to be add is also very small, say 2% and thus a bag of cement will require only about 10 N of such compound.