One of the basic requirement in case of all buildings is that the structure should remain dry as far as possible. If this condition is not satisfied, it is likely that the building may become un-habitable and unsafe from structural point of view. Hence in order to prevent damp into a building, courses provided at various levels of entry of damp into a building which is known as damp-proofing. Thus the provision of damp-proofing courses prevent the moisture entry into the building.

Causes of dampness : Various causes which are responsible for the entry of dampness in a structure are as follows :

1. Rising of moisture from the ground:
The ground on which the building is constructed may be made of soils which easily allow water to pass. Usually, building materials used for foundations, absorb moisture from capillary motion. Thus dampness finds its way to enter into a building.

2. Action of rain :
If the faces of wall exposed to heavy shower of rain, are not suitably protect, they become sources of entry of dampness in a structure. Similarly leaking of roof a also permits  rain water to pass through.

3. Exposed tops of walls :
Parapet walls and compound walls should be provide with a damp-proof course on their exposed tops of such walls may lead to serious results.

4. Condensation :
The process of condensation takes place when warm humid air is cooled. This is due to the fact that cool air can contain less invisible water vapour than warm air. The moisture is deposited on the walls, floors and ceilings. This is the main source causing dampness in badly designed kitchens.

5. Miscellaneous causes :
  • If the structure is located on a site which cannot be easily drained off, dampness will enter the structure.
  • The orientation of a building is also an important factor. the walls obtaining less sunshine and heavy showers of rain are liable to become damp.
  • Newly constructed walls remain damp for a short duration.
  • Very flat slope of roof may also lead to penetration of rain water into roof.

Effects of dampness : The structure is badly affected by dampness. The prominent effects of dampness is given below.

1. A damp building creates unhealthy conditions for those who occupy it.

2. The metals used in the construction of the building are corroded.

3. Unsightly patches are formed on the wall when walls comes in contact to dampness.

4. Decay of timber takes place rapidly due to dry rot in a damp atmosphere.

5. The electrical fittings get deterioration.

6.It promotes and accelerates the movement of termite.

Materials 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. Good asphalt is a very durable and completely impervious material. It is liable to squeeze out in very hot climate or under heavy 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 layer of cement mortar. An overlap of 10 cm is provided at the joint and full overlap provided at all corners. It can accommodate slight movements. But it is liable to squeeze out under heavy pressure and it offers little resistance to sliding.

4. 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.

5. Stones :
Course of stones such as granites, slates etc. laid in cement mortar with vertical breaking joints can work as an effective damp-proofing course.


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