Materials Used For Damp-proofing:
An effective damp proofing material should have the following properties:
1. It should be impervious.
2. It should be strong and durable and should be capable of withstanding both dead as well as live loads without damage.
3. It should be dimensionally stable.
4. It should be free from deliquescent salts like sulphates, chlorides and nitrates.
The materials commonly used to check dampness can be divided into the following four categories:
1. Flexible material: Material like bitumen felts ( which may be hessian based or fibre/glass fibre based), plastic sheeting ( polythene sheet) etc.
2. Semi-rigid Materials: Materials like mastic asphalt or the combination of materials or layers.
3. Rigid Materials: Materials like first class bricks, stones, slate, cement concrete etc.
4. Grout: Consisting of cement slurry and acrylic based chemicals/polymers.
Selection Of Materials For DPC:
The choice of material to function as an effective damp-proof course requires a judicious selection. It depends on several factors such as climatic and atmospheric conditions, nature of the structure and situation where DPC is to be provided. The points to be kept in view while making the selection of DPC materials are briefly discussed below.
1. DPC Above Ground Level:
In ordinary buildings, plinths are usually provided above the ground level. For DPC above ground level, all four types of materials discussed earlier can be used.
At plinth level, 40 mm to 50 mm thick layer of 1:2:4 cement concrete is treated as the best material for normal conditions. When more damp conditions are to prevail rich mixed concrete can be used. Some waterproofing materials such as pudlo, impermo etc can be used during concrete mixing to make the concrete thicker. Normally one or two coatings are applied to the dried surface of the concrete layer.
2. DPC Material For Floor Roofs Etc:
In case of large area such as under floors, over roofs are to be covered by DPC, bitumen felts or mastic asphalt are most common in use. But ensure that their joints are lapped and scaled properly.
3. DPC Material For Cavity Walls:
In case of cavity walls, flexible materials such as copper strips, bitumen sheets, lead strips, etc can be used as the material of DPC. At the base level of the cavity, just around the foundation from where the cavity is started, bitumenized felt or ordinary mastic asphalt can be used.
4. DPC Material For Situations Where Different Thermal Movements Occur:
In case of parapet walls, most common recommended materials are mastic asphalt, lead sheets, copper sheets, and bitumen felts. But ensure that the DPC materials are adequately flexible to allow slight movement due to the structural settlement.