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Damp Proof Course or DPC is the protective layer applied to prevent the rising of moisture to the walls from the ground due to capillary action. It is usually 2.5 cm thick with a ratio of rich cement concrete 1:1.5:3 or 2 cm thick with cement mortar 1:2 mixed with standard waterproofing material. It is provided from the plinth level to the entire width of the plinth wall, and the quantities are calculated in square meters (length x breadth). Usually, DPC is not provided at the sills of doors and verandah openings, for which deductions are made. In most cases, 1 kg of cem-seal, Impermo, or another definitive waterproofing compound is used per bag of cement.
Fig 1: DPC laying
The damp proof course is composed of cement, coarse sand, and stone aggregate in a ratio of 1:1.5:3 with 2% impermo, cem-seal, or Acco proof by weight of cement or another standard waterproofing compound (1 kg per bag of cement). The damp proof course should be applied in a horizontal layer of 2.5 cm thickness at the plinth level. Fresh portland cement, as per traditional standards, is used in preparing DPC. The sand to be used must be clean and coarse, with a particle size of 5 mm or less, and the stone aggregate must be solid and rigid, with a particle size of 20 mm, well-graded, and free of dust and filth. Composeal, pudlo, cico, and other typical waterproofing compounds may be used, with the quantity following the manufacturer’s instructions.
By measuring with measuring boxes, mixing is done on a masonry platform or a sheet-iron tray in the proportion of 1:1.5:3. The cement is first wholly mixed with the waterproofing compound to the desired quantity, then dried and blended in a ratio of 1:1.5 with the sand. The cement and sand mixture is then dry mixed with stone aggregate in the proportion of 1:1.5:3. Clean water is gently and gradually added to the needed quantity while stirring to produce a plastic mix with the required workable consistency. To achieve a uniform and homogenous concrete mixture, the mixing must be done at least three times.
While laying the damp proof course, the level of the plinth’s surface must be checked longitudinally and transversely. The damp proof course should be applied to the top of the walls with frogs of the brick downward. Side forms or shuttering of 2.5 cm thick and solid wooden battens should be fixed firmly and adequately on both sides to confine the concrete so that the shuttering is not disturbed during compaction and mortar does not leak through. To prevent concrete from adhering to the inner edges of the shuttering, it must be oiled. Before laying concrete, the wall’s surface must be cleaned, and the masonry must be wetted with water.
The concrete must be applied within half an hour of mixing and thoroughly compacted by tamping to produce dense concrete level both longitudinally and transversely. After two hours of laying, the concrete surface should be rough and chequered in order to form a key with the wall above. The damp-proof course must be applied in one continuous day with no joints. If in case joints or breaks are unavoidable, they must be provided at the sills of doors or openings. If joints cannot be avoided, they must be sloped, and the sloped surface must be applied with neat cement wash just before the next day’s concreting. After three days, the shuttering can be removed. When the shuttering is removed, the edges should be smooth and free of honeycombing.
The damp proof course is to be watered and kept wet for 7 days before the wall’s construction can begin. Before beginning masonry, the surface must be cleaned and wetted to apply the damp proof course with a smooth texture.
Painting with Asphalt
If specified, two coats of asphalt paint may be applied to the upper surface of the damp proof course. When the concrete is dry, it is required to apply the first coat of hot asphalt at 1.5 kg per sq m (15 percent kg per sq ft) uniformly to the surface. The painted surface is immediately blinded with coarse sand, and the texture is lightly tamped. The second coat of hot asphalt should be applied uniformly at 1 kg per sq m (10 kg per sq ft), and the surface should be immediately blinded with coarse sand and lightly tamped.
2 cm Damp proof course
The damp proof course can be a 2 cm (4″) thick layer of 1:2 cement and coarse sand mortar with standard waterproofing compound at a rate of 1 kg per cement bag. The mixing, laying, curing, and so on must be carried out in the same manner. The form or shuttering must be two centimeters thick so that the DPC can be laid down at a perfect level.
Some common materials used in the Damp Proof Course
Fig 2: Hot Bitumen
Courtesy: Exporters India
Fig 3: Mastic Asphalt
Courtesy: Southern Damp Proofing
Fig 4: Bitumen felt
Combination of sheets and bituminous felts – When the lead foil is sandwiched between asphaltic or bituminous felts used as a DPC, it can prove effective. This combination, known as the leading core, is easy to lay, durable, efficient, economical, and crack resistant.
Dampness in buildings can lead to the attack of termites, rusting and corrosion of metal fittings, cracking in walls, electrical fittings getting damaged, leaking sealants, and many more problems that can lead to loss of money when not treated in time. There are many methods of DPC that can be applied to prevent dampness of any form inside the building. It can hinder future construction works, too, if implemented in the building for extending rooms, changing the house plan, etc. Thus, the Damp Proof Course must be of good quality and sturdy.
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