Basics in Building Construction

Basics in Building Construction 4(2+2)

Lesson 04 : Damp Proofing : Methods And Materials

Materials For Damproof Course

Following are the materials which are commonly used for damp-proofing.

1. Hot bitumen
   This is a flexible material and is placed on the bedding of concrete or mortar. This material should be applied with a minimum thickness of 3 mm.


2. Mastic asphalt
   This is a semi-rigid material and it forms an excellent impervious layer for damp-proofing. It can withstand only very slight distortion. It is liable to squeeze out in very hot climates or under pressure.


3. Bituminous felts
   This is a flexible material. It is easy to lay and is available in rolls of normal wall width. It is laid on a layer of cement mortar. An overlap of 10 cm is provided at the joints and full overlap is provided at all concerns. The laps may be sealed with bitumen, if necessary. Bitumen felt can accommodate slight movements. But it is liable to squeeze out under heavy pressure and it offers little resistance to sliding.


4. Metal sheets
   The sheets of lead, copper and aluminum can be used as membranes for damp-proofing.


5. Combination of sheets and felts
   A lead foil is sandwiched between asphalt or bituminous felt. This is known as lead core and it is found to be economical, durable and efficient.


6. Stones
   Two courses of sound and dense stones such as granites, slates, etc. laid in cement mortar with vertical breaking joints can work as an effective damp – proofing course. The stones should extend for full width of the wall. Sometimes stones can be fixed, as in case of roof surfaces, on the exposed faces of the wall etc.


7. Bricks
   Dense bricks, absorbing water less than 4 1/2 % of their weight, can be used for damp-proofing at places where damp is not excessive. The joints are kept open. Such bricks are widely used when a damp-proofing course is to be inserted in an existing wall.


8. Mortar
   For plastering work, the water-proof mortar can be prepared. It is prepared by mixing 1 part of cement, 2 parts of sand and pulverized alum at the rate of 12 kg per m3 of sand. In the water to be used, 75 gm of soft soap is dissolved per litre of water and this soap water is then added to the dry mix. The mortar thus prepared is used to plaster the surfaces. Alternatively, some patented water-proofing material such as Pudlo, Cico, Dempro, etc. may be added to the cement mortar.


9. Cement concrete
   A cement concrete layer in the proportion 1:2:4 is generally provided at the plinth level to work as damp-proofing course. The depth of cement concrete layer varies from 40 mm to 15 cm. It stops the rise of water by capillary action and it is found to be effective at places where damp is not excessive.