DAMP Prevention

Presence of hydroscopic moisture on a surface is called dampness. In general dampness causes unhygienic conditions, affects the health and comfort of inhabitants. Further, it deteriorates the stability of the damped surface. Thus, it is an essential feature in construction to prevent dampness.

Sources of Dampness

Dampness in a building may be caused due to natural causes or structural causes.

1. Natural Causes

Natural causes may be due to:

1. Penetration of rain
2. Rise of moisture from ground
3. Moisture condensation
4. Drainage condition of the site
5. Orientation of the building

(i) Penetration of Rain

Rain may penetrate a building through the top of the walls, through the surface of the walls and through the roof. Rain may penetrate the unprotected parapet walls of a building during heavy rains.

(ii) Rising of Moisture from the Ground

The ground or sub-soil on which a building is constructed may give an access to water to enter the structure and cause dampness. Gravel and sandy soil are highly permeable and allow water to pass through them easily. But clay and clayey silt or clayey sand are less permeable but cause dampness due to heavy capillary rise.

(iii) Moisture Condensation

Whenever the warm air in the atmosphere is cooled, the process of condensation takes place. Because of this condensation, moisture is deposited on the areas of walls, floors and ceilings.

(iv) Drainage Conditions of the Site

The elevation of a ground on which a building is constructed has significance on dampness condition. Buildings built on a higher ground can be drained easily and are, hence, less liable for dampness. Low-lying sites can not be drained easily and may cause water logging. The condition will get still worse if impervious soil is present beneath the structure. Hence, it is an essential condition to be looked into before starting any construction.

(v) Orientation of the Building

Depending on the climatic conditions and monsoon walls of buildings may be subjected to constant splash of rain water. Hence, the construction of a building should be accordingly planned.

2. Structural Causes

Structural causes may be due to faulty design of the building, faulty construction, poor workmanship or use of inferior quality material in construction.

(i) Faulty Design of Structure

Improper mix design of concrete not only has less strength but of high permeability causing dampness. Improper mortar proportions may also cause water penetration. Non-provision may also cause water penetration. Non-provision of a damp-proof course in the design and improper plinth-protection measures may cause dampness in the building.

(ii) Faulty Construction of Structure

Improper construction of various parts, for example, fixtures in a building, joints in the roofs, throating of sills and copings, joining of walls, etc., may cause dampness by entry of water.

(iii) Poor Workmanship and Materials

Skilled workers should be used for construction of walls, roofs, floorings, etc., and electrical and plumbing works. Further, good quality materials should be used to get effective construction.

Effects of Dampness

In general, presence of dampness results in poor functional performance, shabby appearance and structural weakness. Following are the effects of dampness:

1. Presence of damp conditions causes efflorescence on the surfaces leading to disintegration of bricks, stones, tiles, etc., and in reduction of strength.
2. Plastering may get softened or crumbled due to dampness.
3. Paints on surfaces may get blistered, bleached and disfigured.
4. Dampness may cause corrosion of metals used in the construction.
5. Materials used as floor coverings, such as tiles, marble stones, etc., may be damaged due to loss of adhesion with the floor bases.
6. Doors and windows and other timber works may get warped due to dampness.
7. All electrical fittings get deteriorated and liable to cause short circuits.
8. Dampness promotes the growth of termites and hence deteriorates materials and causes unhygienic conditions.
9. Dampness added with warmth and darkness leads to breeding of germs which may cause some disease.
10. Dampness creates an unhygienic working condition for the occupants.

Methods of Damp-proofing

Damp-proofing courses (DPC) of suitable materials are provided at appropriate locations for their effective use (Sharma, 1988). DPC prevents basically the entry of the water from ground in buildings. The best position for DPC is the plinth level in buildings.

Following general principles should be adopted while providing DPC in buildings:

1. DPC should cover the full thickness of the wall.
2. Mortar bed on which the DPC is laid should be level and there should not be any projection.
3. In places where a vertical DPC is provided, it is to be laid continuously with a horizontal DPC and a fillet.
4. DPC course should be continuous and should form as a bearer from the entry of moisture.
5. DPC should not be exposed in total.

DPC Treatment in Buildings

Provision of damp proof course at plinth level is shown in Fig. 29.2, whereas Fig. 29.3 shows the DPC in basement.

Figure 29.2 DPC above ground level

Figure 29.3 DPC in basement

Prevention of damp along parapet walls and flat roof are shown in Figs. 29.4 and 29.5.

Figure 29.4 DPC in parapet wall

Figure 29.5 DPC in flat roof

Materials used for DPC

Materials generally used for DPC are flexible materials like, hot bitumen, bituminous felts, bituminous sheets, polythene sheets, metal sheets of lead, copper, etc.; semi-rigid materials like mastic asphalt or combination of materials or layers and rigid materials like first-class bricks, stones, slates in courses and cement-concrete stones, slates in courses and cement-concrete or mortar layers, etc.

Damp-proof Surface Treatment

In this method the surface exposed to moisture is treated by providing a thin film of water-repellent material over the surface. Such a surface treatment may be external or internal. Generally the external treatment is more effective in damp prevention when compared to internal treatment.

Surface treatments include pointing, plastering, painting, distempering, etc., Lime-cement plaster mix (1 cement:1 lime:6 sand proportion) is more effective.

Materials used for surface treatment are sodium or potassium silicates, aluminium or zinc sulphates, barium hydroxide and magnesium sulphate, soft soap, linseed oil, coal tar, soap, bitumen, remix and gums, etc., applied in alternate layers with suitable combination depending on the climatic conditions.

Integral Damp-proofing Treatment

In this process certain compounds are added along with concrete or mortar while mixing which when used in construction act as barriers to moisture penetration.

The added materials function based on different principles. Based on the mechanical principle, materials like chalk, talk, fullers earth, etc., fill in the pores present in the concrete or mortar and make the concrete or mortar and set as a waterproofing agent. Based on the chemical reaction principle, the materials like alkalines, silicates, aluminium sulphates, calcium chloride, etc., react chemically as water-resistant. Based on the repulsion principle, the materials like soaps, petroleum oils, fatty acid compounds such as stearates of calcium, sodium, ammonium etc., which when added with concrete or mortar react with it and become water repellent.