Selection of Material for D.P.C.

Any materials to be used as D.P.C must possess following properties. They should be

• impervious
• strong and durable to register loads
• dimensional is stable
• free from Salt Lake sulfates chlorides and nitrates

There are commonly 4 types of materials that can be used at DPC

1. Flexible material (Bitumen felts, plastic sheeting etc)
2. Semi-rigid material (Mastic asphalt)
3. Rigid materials (Layer of brick, stone or concrete)
4. Grouting materials (Cement slurry)

But before choosing any of the above mentioned materials, the following three points must be considered and then the choice has to be finalized.

• Climatic and atmospheric condition
• Nature of structure
• Building components where DPC is to be provided

Below are mentioned some of the key points that will help you select materials to use as damp proof course or DPC.

1. DPC Material Above Ground Level

Generally cement concrete is used as DPC above ground level. This type of DPC is applied at plinth level. For normal climatic conditions a 25 to 50 mm thick layer of cement concrete of grade M15 (1:2:4) can be used.

For the humid and damp conditions a higher grade of concrete can be used as DPC.

While designing concrete; waterproofing materials like Pudlo or Impermo etc can also be added to make the concrete more impervious.

For better protection apply two coats of hot bitumen over the dried surface of concrete.

2. DPC Materials for Floors and Roofs

In case of flat or large areas (such as floor and roofs) or walls having thickness more than 40 cm, it is advised to use flexible or semi rigid types of DPC materials. Because in this type of material provide lesser number of joints.

Any flexible materials such as mastic Asphalt, bitumen felt or plastic sheets can be used.

When using these materials as DPC, make sure that they bonded properly with the surface and all the joints are lapped and sealed properly.

3. DPC  for Areas Experiencing Differential Thermal Movement

Differential thermal movement occurs when two building components which are joined together (such as parapet walls and roof) experience different amount expansion.

Use of flexible type of DPC materials such as Mastic asphalt or Bitumen felts is a good choice in these cases.

4. DPC Materials for Cavity Walls

In case of cavity wall construction, the cavity over the door or Window should be bridged by flexible materials like bitumen felt or strips of lead etc.

5. DPC for Expansion and Contraction Joints

If expansion and contraction joints present in the RCC slab or retaining walls of the basement, then they must be sealed using PVC or GI sheets. This will prevent movement of sub-soil water into the building.

Reference

Building Construction by Sushil Kumar