Dampness, seepage or leakage of any sort in a wall or roof of the house is something that a house owner dreads the most. Remedies are available for these problems and locating the source of these is more important than plugging a leakage or covering seepage or dampness. In a three-part series on this most common problem in flats as well as in individual houses, we will be covering different aspects of this problem:
Spot the difference
First of all it is important to know the difference between leakage and seepage. Seepage doesn’t require any cracks or passage in walls or roof of the house. It occurs when the wall or slab is porous and water appears on its surface by escaping through the wall or slab. Leakage occurs when there is a crack or hole in the wall or roof. So leakage occurs when water has a clear passage to pass through. In general, seepage leads to damp patches while leakage leads to drippings.
Causes: Leaking of a water supply pipe joint, crack in a sanitary pipe or leakage of its joint, blockage of a drainage pipe are common causes of appearance of damp patches on the walls. Often, a rainwater pipe gets blocked and rain water finds its way into the porous brickwork of the wall through some hair line crack in the pipe or its not-so-water-tight joints. Sometimes, the mouth of the rainwater pipe gets choked with dust or leaves or some debris on the roof. In that case, the rain water accumulates on the roof and finds its way into the slab through a broken grout in tile or stone joints in the terrace surface and appears on the ceiling. In some cases, the water gets trapped on concrete slab surface below the terrace topping and then begins to drip through a crack or a fan hook. Such a problem, when not attended to for a long time, leads even to the corrosion of reinforcement in the slab.
Areas: Wall areas containing water-supply pipes, rainwater pipes or sanitary pipes are the most prone to leakage or seepage of water. Roof slab corners near the rainwater pipes are also common areas for these problems as water collects on the roof slab due to blockage of its entry to rain ater pipe.
Dripping of water from a fan hook or a crack in the roof slab is also common.
In such a case, locating the exact spot of the leakage takes the maimum time. It is not necessary that the entry of water is exactly above the dripping point. Sometimes, water keeps accumulating in a hidden gap and starts dripping when sufficient pressure gets built while the terrace gives no signs of the point of its entry. Sunken slabs of toilets are also vulnerable areas from where leakages may happen.
Avoiding leakages: Prevention they say is better than cure. The same is applicable to the house also. The best remedy for avoiding leakages and seepages is to take extra care during construction of the house itself and eliminate all chances of occurrence of these by making susceptible areas water-proof. The areas to be given special attention are the Basement; Damp Proof Course (DPC); sunken slabs, if any, water -supply pipes, sanitary pipes, rain water pipes, AC drain pipes, roof slab, parapet joints and floor joints with walls. Still, if leakage or seepage occurs somewhere in the house, the right method of stopping it is to locate the root cause and plugging it instead of simply treating the damp or dripping surface with some chemical as such treatment will give only temporary relief.
(Part II— Avoiding leakage and seepage in pipes and roof slab) This column is published fortnightly
Let us consider the various elements of the house and the preventive measures to be taken in each of them:
Basement: While constructing a basement, care has to be taken to build a damp-proof structure that doesn’t allow ingress of water. For it, the walls of the basement should be raised in Reinforced Cement Concrete (RCC) only. The concrete used in RCC should be M20 or of ratio 1:1.5:3 for cement, coarse sand and crushed stone. Proper vertical and horizontal reinforcement should be provided on both faces of RCC walls to bear the vertical loads from the structure and the earth pressure on the outer face of walls to avoid any cracks in them. Water proofing compound should be added to all the concrete laid in basement foundation and walls. The water proofing compound should be from a reputed company and shouldn’t have crossed expiry date. For a 50 kg cement bag, 1 to 1.5 kg of water proofing compound is required. It should be mixed in concrete as per directions of the supplier written on the container.
The joints in walls should be treated with acrylic polymer bonding agent mixed with cement and silica. The outer surface of RCC walls should be painted with two coats of water proofing epoxy paint. Such paints are better than bitumen as these become rubber-like on drying while bitumen turns hard. The basement flooring should include laying of double layer of polythene sheet over the compacted sand before laying RCC layer over it. 12 mm thick thermocole sheet pieces should be inserted between the RCC layer and the basement walls all along the periphery of the basement area.
Damp Proof Course: The provision of a damp proof course (DPC) at plinth level of the house saves its walls from ‘rising dampness’ through capillary action as the bricks used in foundations are porous in nature. For house area, where RCC basement has not been provided and brick foundations have been raised, a 1.5-inch thick concrete Damp Proof Course (DPC) should be laid on foundation walls at plinth level. The concrete used should be 1:1.5:3 and water proofing compound should be added to it. Only 10 mm size coarse aggregate should be used in the concrete in view of its small thickness. Its water content should be kept low to avoid flowing out of cement slurry. All external walls should be provided with vertical DPC on their inner side. Vertical DPC is in 1:3 cement mortar and not in concrete. It is very important to provide vertical DPC to prevent rise of moisture. After the curing of DPC is over and it has become dry, two layers of bitumen should be applied over the DPC by using 85/25 grade bitumen.
Immediately after applying bitumen, sand should be applied over it. Preference should be given to use of polymer modified material coating instead of bitumen over the DPC. It can be applied with a brush and on wet surface also.
Sunken floors: Sunken floors are provided in the toilets to accommodate the depth of Indian type water-closets.
Sunken floors are often a cause of leakage and dampness in houses if proper water-proofing treatment is not given to them. As more and more Indians prefer to provide European pans only, the concept of sunken floors is fast vanishing. Yet some Indians living at upper floors choose to have an Indian seat only and in their case, the slab of the toilet area is sunk to a lower level. Sunken floors should be treated with a water-proofing cream like paste prepared by mixing of 1 part of acrylic emulsion (liquid) and 2 parts of polymer modified cement (powder). 2 coats of this paste should be applied with brush on the slab surface and walls up to 6 inch height above toilet floor level. This mix can be applied even on wet slab. On drying, it forms a flexible water proofing film. Otherwise, a readymade synthetic membrane can be laid on the slab. Such membranes however need to be notched into the walls.
The water proofing application should now be covered with a ½ inch thick 1:3 cement sand plaster and cured well.
Over the cured plaster surface, two coats of 85/25 grade bitumen should be applied after the drying of plaster.
After the application of bitumen, a PVC sheet should be laid over it immediately so that the sheet sticks to the surface. Only after this treatment, should the sunken area be filled with clinker or foam concrete up to the bottom level of the flooring sub base.
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