Damp proof course DPC | Causes of dampness in a building

Damp proof course

A continuous water proof layer is provided above the ground level to prevent moisture to come up which is called damp proof course or DPC. Damp proof courses are provided at various levels of entry of damp into a building.  Provision of DPC prevents of entry of moisture from walls floors and basement of a building.

Causes of dampness

• Rising of moisture from the ground.
• Rain travel from wall tops.
• Heavy rain shower on external walls.
• Poor drainage, imperfec t orientation, imperfect roof slope, defective construction etc.
• Bricks have a porous structure. The pores of bricks are interconnected to form capillaries. That is why bricks suck dampness from soil underneath and pump it to upper parts of the building due to capillary force.

Harmful Effects of dampness

• With dampness cement sand mortar destroy and concrete also deteriorate reducing the strength of the structure.
• After some time plaster falls down and surface treatments such as white washing, painting or wallpapers  are damaged. This caused the unpleasant appearance.
• Further this dampness causes insect and germ growth and is not good for health of inhabitants.

If there is direct contact between the underneath brickwork and brickwork of the super structure whole of the building will be affected.

Materials used for damp proofing

DPC thickness varies from 1.5 inch for residential buildings to 3 inch  for official construction. It is a layer of P.C.C.(1:2:4) over which two coats of hot bitumen are applied. For load bearing walls, polythene sheet is also provided. The top of DPC should be at the same level as that of floor top of the building.

D.P.C is provided on all the walls which are continuous above plinth level.

Characteristics of ideal damp proofing material

• It should be perfectly impervious.
• It should be durable.
• It should be strong and capable of resisting superimposed loads on it.
• It should be flexible so that it can accommodate structural movements without any fracture.
• It should remain in its position when applied.
• It should not be costly.

General principles while providing D.P.C.

• It may be horizontal or vertical.
• Horizontal D.P.C. should cover full thickness of walls excluding finishing.
• At junctions and corners of walls, horizontal damp proof course should be laid continuous.
• Mortar bed supporting damp proof course should be levelled and free of projections so that DPC may not be get damaged.
• D.P.C. should not be exposed on walls surface, because it may get damaged during finishing work.
• When a horizontal DPC is continued to a vertical face, a cement concrete fillet of about 75 mm radius should be provided at the junction.