DAMP PROOFING
SOURCES OF DAMPNESS
Dampness in buildings is generally due to one or more of the following reasons:
1. Faulty design of the structure
2. Faulty construction or poor workmanship
3. Use of poor materials in construction
These causes give rise to easy access to moisture to enter the building from different points, such as rising of moisture from the ground and rain penetration through walls, roofs and floors. The moisture entering the building from the foundation and roofs travels in different directions further under the effects of capillary action and gravity, respectively. The entry of water and its movements, in different parts of the building, are positively due to one or more of the causes listed above. The various sources that create dampness in buildings are as follows.
Rising of moisture from the ground
The sub-soil or ground on which the building is constructed may be made of soil that easily gives access to water to create dampness in buildings, through the foundations. Generally, foundation dampness is caused when the building structures are constructed on low-lying waterlogged areas, where a sub-soil of clay or peat is commonly found, through which dampness would easily rise under capillary action unless properly treated. This dampness further finds it's way to the floors, walls, etc. through the plinth.
Action of rainwater
Whenever the faces of walls are not suitably protected from the exposure to heavy showers of rains, they become the sources of dampness in a structure. Similarly, the poor mortar joints in walls and cracked roofs also allow dampness to enter a building structure. Sometimes, due to a faulty eave board, the rainwater may percolate through roof coverings.
Rain penetration from tops of walls
All parapet walls and compound walls of buildings, which have not been protected from rain penetration by using damp-proof course or by such measures on their exposed tops, are subjected to dampness. This dampness in buildings is of serious nature and may result in unhealthy living conditions or even in structurally unsafe conditions.
ALSO READ: Materials Used For Damp Proofing (DPC) | What Are The Materials Used For DPC?
Condensation due to atmospheric moisture
Whenever the warm air in the atmosphere is cooled, it gives rise to the process of condensation. On account of the condensation, the moisture is deposited on the whole area of walls, floors and ceilings. However, this source of dampness is prevalent only in certain places in India, where very cold climates exist.
MISCELLANEOUS SOURCES OR CAUSES
The various other sources or causes, which may be responsible for dampness in buildings are mentioned below:
a. Poor drainage of the site: The structure is located on low-lying sites cause waterlogged conditions when impervious soil is present underneath the foundations. Therefore, such structures that are not well-drained cause dampness in buildings through the foundation.
b. Imperfect orientation: Whenever the orientation of the building is not proper or geographical conditions are such that the walls of the building get less direct sunrays and more heavy showers of rain, then such walls become liable to dampness.
c. Constructional dampness: If more water has been introduced during construction or due to poor workmanship, the walls are observed to remain in a damp condition for sufficient time.
d. Dampness due to defective construction: The dampness in buildings is also caused due to poor workmanship or methods of construction, namely inadequate roof slopes, defective rainwater pipe connections, defective joints in the roofs, improper connections of walls, etc.
EFFECTS OF DAMPNESS
1. A damp building creates unhealthy living and working conditions for the occupants.
2. Presence of damp conditions causes efflorescence on building surfaces, which ultimately may result in the disintegration of bricks, stones, tiles, etc., and hence in the reduction of strength.
3. It may result in softening and crumbling of plaster.
4. It may cause bleaching and flaking of the paint, which result in the formation of coloured patches on the wall surfaces and ceilings.
5. It may result in the corrosion of metals used in the construction of buildings.
6. The materials used as floor coverings, such as tiles, are damaged because they lose adhesion with the floor bases.
7. Timber, when in contact with damp conditions, gets deteriorated due to the effects of warping, buckling and rolling.
8. All electrical fittings get deteriorated, causing leakage of electric current with the potential danger of a short circuit.
9. Dampness promotes the growth of termites and, hence, creates unhygienic conditions in buildings.
10. Dampness, when accompanied by warmth and darkness, breeds the germs of tuberculosis, neuralgia, acute and chronic rheumatism, etc., which sometimes result in fatal diseases.
TECHNIQUES AND METHODS OF DAMP PREVENTION
The following precautions should be taken to prevent the dampness in buildings before applying the various techniques and methods described later:
1. The site should be located on high ground and well-drained soil to safeguard against foundation dampness. It should be ensured that the water level is at least 3 m below the surface of the ground or lowest point even in the wet season. For better drainage, the ground surface surrounding the building should also slope away from the house or structure.
2. All the exposed walls should be of sufficient thickness to safeguard against rain penetration. If walls are of bricks, they should be made of at least 30 cm thickness.
3. Bricks of superior quality, which is free from defects such as cracks, flaws and a lump of limestones, should be used. They should not absorb water more than one-eighth of their own weight when soaked in water for 24 hours.
4. Good quality cement mortar (1 cement:3 sand) should be used to produce a definite pattern and perfect bond in building units throughout the construction work. This is essential to prevent the formation of cavities and the occurrence of differential settlement, due to inadequate bonding of units.
5. Cornices and string courses should be provided. Window sills, coping of plinth and string courses should be sloped on the top and throated on the underside to throw the rainwater away from the walls.
6. All the exposed surfaces like tops of walls and compound walls should be covered with waterproofing cement plaster.
7. Hollow walls (i.e., cavity walls) are more reliable than solid walls in preventing dampness and, hence, cavity wall construction should be adopted wherever possible.
PREVENTION OF DAMPNESS
The various techniques and methods, generally adopted to prevent the defects of dampness, are as follows:
a. Use of damp-proofing courses (DPC) or damp-proofing membranes.
b. Waterproof or damp-proof surface treatments.
c. Integral damp-proofing treatments.
d. Cavity walls or hollow walls.
e. Guniting or shot concrete, or shotcrete.
f. Pressure grouting or cementation.
USE OF DAMP-PROOFING COURSES
These are the layers or membranes of water repellent materials, such as bituminous felts, mastic asphalt, plastic sheets, cement concrete, mortar, metal sheets, slates and stones, which are interposed in the building structures at all locations wherever water entry is anticipated or suspected. These damp-proof courses of suitable materials should be provided at appropriate locations for their effective use. Basically, DPC is provided to prevent the water from rising from the sub-soil or ground and getting into the different parts of the building. The best location or position for DPC, in the case of buildings without basements, lies at the plinth level or, in the case of structures without a plinth, it should be laid at least 1.5 cm above the ground level. These damp-proof courses may be provided horizontally or vertically in floors, walls, etc. In the case of basements, the laying of DPC is known as ‘tanking’.
Waterproof (or damp proof) surface treatments
The surface treatment consists of filling up the pores of the material exposed to moisture by providing a thin film of water repellent material over the surface. The surface treatments can be either external or internal; the external treatment is effective in preventing dampness whereas internal-only reduces it to a certain extent.
Many surface treatments like pointing, plastering, painting and distempering are given to the exposed surfaces and also to the internal surfaces. The most commonly used treatment to protect walls against dampness is lime cement plaster of (1 cement:1 lime:6 sand) mix proportions. A thin film of waterproofing material can be applied to the surface of the concrete after it is laid. Some of the materials generally employed as water- proofing agents in surface treatments are sodium or potassium silicates, aluminium or zinc sulphate, barium hydroxide and magnesium sulphate in alternate applications, soft soap arid alum also in alternate applications, lime and linseed oil, coal tar, bitumen, waxes and fats, resins and gums, etc.
Integral damp-proofing treatment
The integral treatment consists of adding certain compounds to the concrete or mortar during the process of mixing, which when used in construction act as barriers to moisture penetration under different principles. Compounds like chalk, talc and fuller’s earth have a mechanical action principle, i.e., they fill the pores present in the concrete or mortar and make them denser and waterproof. The compounds like alkaline, silicates, aluminium sulphate and calcium chlorides work on a chemical action principle, i.e., they react chemically and fill in the pores to act water resistant. Similarly, some compounds like soaps, petroleum oils and fatty acid compounds such as stearates of calcium and sodium ammonium work on a repulsion principle, i.e., they are used as admixtures in concrete to react with it and become water repellent.
Cavity walls (or hollow walls)
A cavity wall consists of two parallel walls or leaves or skins of masonry separated by a continuous air space or cavity. Cavity walls consist of three main parts, namely,
i. The outer wall or leaf (10 cm thick) is the exterior part of the wall.
ii. The cavity or air space of 5–8 cm.
iii. The inner wall or leaf (minimum 10 cm) is the interior part of the wall.
The two leaves, forming the cavity in between may be of equal thickness or the thickness of the inner leaf maybe increased to take the greater proportion of the imposed loads transmitted by the floor and roof. The provision of the continuous cavity in the wall efficiently prevents the transmission or percolation of dampness from the outer wall or leaf to the inner wall or leaf. Based on the climatic conditions in India, i.e., hot dry (hot-humid), this cavity type of construction is most desirable as it offers many advantages such as better living and comfort conditions, construction economy and preservation of the building against dampness.
The cavity wall construction offers the following advantages over solid wall construction:
i. As there is no contact between the outer and inner walls of a cavity wall except at the wall ties, which are of impervious material, the possibility of moisture penetration is reduced to a minimum. It has been established that a cavity wall having 10 cm thick internal and external leaves with 5 cm cavity or air space in between is better and more reliable than a solid wall of 20 cm thickness, in respect of damp penetration.
ii. As air in the cavity is a non-conductor of heat, it prevents the transmission of heat through the walls and maintains better consistency of temperature inside the building. In this regard, it has been established that cavity walls provide an improvement of 25 per cent in heat insulation over the solid walls of the same cross-section less the cavity thickness. Therefore, cavity wall construction is best suited for a tropical country like India.
iii. The cavity walls also offer good insulation against sound.
iv. The cavity tends to reduce the nuisance of efflorescence.
v. This type of construction also offers many other benefits such as economy, better comfort and hygienic conditions in buildings.
Guniting (or shot concrete)
This consists of forming an impervious layer using a rich cement mortar (1 cement:3 sand or fine aggregate mix) for waterproofing over the exposed concrete surface or over the pipes, cisterns, etc., for resisting the water pressure.
Gunite is a mixture of cement and sand or well-graded fine aggregate, the usual proportions being 1:3 or 1:4 (i.e., 1 cement:(3 or 4) sand or fine aggregate). A machine known as a cement gun, having a nozzle for spraying the mixture and a drum of compressed air for forcing this mixture under desired pressure, is used for this purpose. Any surface, which is to be treated, is first thoroughly cleaned of any dirt, grease or lose particles and then fully wetted. The mixture of cement and sand or aggregates is then shot under a pressure of 2-3 kg/cm2 by holding the toe nozzle of the cement gun at a distance of 75–90 cm from the surface of the wall. The necessary quantity of water is added by means of a regulating valve soon after the mixture comes out from the cement gun. Thus, the mixture of desired consistency and thickness can be sprayed or deposited to get an impervious layer. This impervious surface should be watered for at least 10 days.
By this technique, an impervious layer of high compressive strength (560–700 kg/cm2 after 28 days) is obtained and, hence, this is also very useful for reconditioning or repairing old concrete works and brick or masonry works, which have deteriorated either due to climatic effects or inferior workmanship.
Pressure grouting (or cementation)
Cementation is the process or technique of forcing the cement grout (i.e., the mixture of cement, sand and water) under pressure into the cracks, voids or fissures present in the structural component or ground. That is, all the components of a structure in general and foundations in particular, which are liable to moisture penetration, are consolidated and, hence, made water-resistant by this cementation process.
In this process, holes are drilled at selected points in the structure and the cement grout, of sufficiently thin consistency is forced under pressure to ensure complete penetration into cracks or voids. This makes the structure watertight and restores its stability and strength to some extent.
Similarly, when the structure is resting on hard but loose textured ground, this process can increase its strength. For this, pipes are driven into the ground, cores within the pipes are removed by means of earth auger and finally the grout is forced (pumped) into the ground to fill the voids, loose pockets, etc.
This technique is also used for repairing structures, consolidating ground to improve bearing capacity, forming water cut-offs to prevent seepage, etc.
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