PROTECTION OF BUILDINGS AGAINST DAMPNESS
One of the requirements of the building is that it should be dry. Dampness in a building may occur due to bad design, faultyconstruction and use of poor quality of materials. Dampness not only affects the life of the building but also creates unhygienic conditions of the important items of work in the construction of a building. The treatment given to prevent leakage of water from roof is generally termed as water proofing whereas the treatment given to keep the walls, floors and basement dry is termed as damp proofing.
DEFECTS OF DAMPNESS IN BUILDINGS:
The various defects caused by dampness to building may be summarized as under:
- It causes efflorescence which may ultimately result in disintegration of bricks, stones, tiles etc.
- It may result in softening and crumbling of plaster.
- It may cause bleaching and flaking of paint with the formation of coloured patches.
- It may result in the warping, buckling and rotting of timber.
- It may lead to the corrosion of metals.
- It may cause deterioration to electrical fittings.
- It promotes growth of termites.
- It creates unhealthy living conditions for the occupants.
CAUSES OF DAMPNESS IN BUILDINGS
Absorption of moisture by the building materials is one of the chief causes of dampness. On acoount of granular nature of materials, moisture finds an easy access through the voids and this aided by capillary action assists the moisture to travel in different directions. Thus, either on account of faulty design of structure or bad workmanship or by use of defective structures or by use of defective materials, moisture may find its way on the interior of the building either through the wall, floor or roof.
SOURCES OF DAMPNESS IN BUILDINGS
The important sources of dampness may be summarized as below:
- Dampness rising through the foundation walling. Moisture from wet ground may rise well above the ground level on account of capillary action.
- Splashing rain water which rebounds after hitting the wall surface may also cause dampness.
- Penetration of rain water through unprotected tops of walls, parapet, compound walls, etc may cause dampness.
- In case of sloped roofs, rain water may percolate through defective roof covering. In addition faulty eaves course and eave or valley gutters may allow the rain water to descend through the top supporting wall and cause dampness.
- In case of flat roofs, inadequate roof slopes, improper rain water pipe connections, and defective junction between roof slab and parapet wall may prove to be the source of dampness.
METHODS OF DAMP PROOFING
Following methods are generally adopted to prevent the defect of dampness in a structure:
- Membrane damp proofing
- Integral damp proofing
- Surface treatment
- Guniting
- Cavity wall construction
(1) Membrane Damp Proofing:
This consists in providing layers of membrane of water repellant material between the source of dampness and the part of the structure adjacent to it. This type of layer is commonly known as dam proof course (or DPC) and it may comprise of materials like bituminous felts, mastic, asphalt, plastic or polythene sheets, cement concrete, etc. Depending upon the source of dampness, DPC may be provided horizontally or vertically in floors, walls, etc. Provision of DPC in basement is normally termed as tanking.
General principles to be observed while laying DPC are:
- The DPC should cover full thickness of walls excluding rendering.
- The mortar bed upon which the DPC is to be laid should be made level, even and free from projections. Uneven base is likely to cause damage to DPC.
- When a horizontal DPC is to be continued up a vertical face a cement concrete fillet 75mm in radius should be provided at the junction prior to the treatment.
- Each DPC should be placed in correct relation to other DPC so as to ensure complete and continuous barrier to the passage of water from floors, walls or roof.