MATERIALS FOR DAMP PROOF COURSE

Damp proof course (DPC) is a barrier of impervious material built into a wall or pier to prevent moisture from moving to any part of the building.

Following are the materials generally used for damp proofing of structures:

1) Flexible Materials:

The materials, which do not crack and deform their shape when subjected to loading, are called Flexible Materials

a) Bitumen Mastic (Mastic Asphalt)

·         It consists of asphalt or bitumen mixed with fine sand in hot state to form an impervious mass.

·         Due to this consistency it can be spread (when hot) to a depth of 2.5cm to 5cm, which sets on cooling.

·         It provides good impervious layer but special care is needed in its laying.

b) Bitumen Felts (Sheets):

·         It consists of 6mm thick sheet of bitumen prepared in rolls having width equal to that of brick wall.

c) Hot laid Bitumen:

This material is used on a bedding of cement concrete or mortar.

·         This should be applied in two layers at the rate of 1.75kg/m² of the area.

d) Metal Sheets:

·         Metal sheets of Copper, Aluminium, or Lead are used to prevent dampness, but they are costly.

·         Sheets of these materials are used throughout the thickness of the wall.

·         The sheets of Lead are laid over Lime Mortar and not with Cement.

·         Mortar due to the chemical reaction of Cement over the Lead.

·         The sheets of metal should be coated with asphalt.

·         The thickness of the sheets should not be less than 3mm.

2) Rigid Materials:

·         The materials, which do not resist transverse stresses and cracks when subjected to sever loading, are known as Rigid Materials.

a) Rich Concrete

·         1.2cm to 4cm thick layer of Rich Concrete (1:2:4) painted with two coats of hot bitumen is used as horizontal D.P.C.

·         It also prevents the moisture penetration by capillary action.

·         These layers are laid where the damp is not excessive.

b) Mortar:

·         2cm thick layer of Rich Cement and Sand Mortar (1:3) is applied on the inner face of external wall.

·         This is a vertical D.P.C.

·         The surface is than painted with two coats of hot bitumen.

c) Bricks:

·         Over burnt or dense bricks in one or two layers can be used as cheap and effective DPC.

·         They are laid in Rich Cement and Sand Mortar (1:3).

·         Bricks are rarely used as DPC except in cheap houses.

d) Stones or Slates:

·         Two layers of stone slabs or slates laid in Lime, Cement and Sand Mortar (1:1:6) make a best DPC.

·         They can also be laid in Cement Sand Mortar.

·         It is used where a good quality of stone is easily and cheaply available.