What Is Dampness In Building?
The presence of gravitational or hygroscopic moisture is known as dampness. One of the basic requirements of good construction is that a building or a structure should be free of dampness. It should not allow moisture to enter the building through the wall, roofs, or floors.
The moisture entering through the cracks of walls, roofs, and floors gives rise to unhygienic conditions such as deterioration of the structure and its components as well.
So it is necessary to prevent dampness from entering the structure. Every structure should be damp-proof. Damp proofing is an important factor of building design, which should be considered during the planning and construction of the structure.
Sources Of Dampness In Buildings
Moisture can enter the building in various ways. The sources of dampness are listed below:
- Dampness can enter the building through the foundation walls from the wet ground on account of capillary action.
- Cracks on the surface of walls, slabs, terraces, roofs, etc., allow the entry of moisture during the rainy season.
- Percolating water through defective roof coverings and leakage in structures.
- Due to accumulation of water on roofs if proper drainage or slope is not provided.
- Due to leakage in plumbing system of the building, water may slowly seep in through the walls or floorings.
Causes Of Dampness In Structures
Various causes of dampness in a building are as given below:
1. Moisture Rising Up The Wall From Bottom (Ground)
All the structures have a foundation as a base to support the structure. The foundation rests on the ground. If the ground or the soil is pervious, the moisture continuously travels through it.
Also, if the soil is impervious the soil has a lot of moisture may be present in it. Through capillary action, the water rises up the wall and the floor. The water in the walls causes damage to the structure.
2. Rainwater Traveling From Wall Tops
If the top portion of the wall is not protected against penetration of water, the rainwater will enter the wall through cracks and will travel down. Leakage in roofs will also permit water to enter.
3. Rain Beating Against The External Wall
If there is heavy rainfall, it strikes the walls, and if the wall is not treated properly, moisture will enter the wall, causing dampness in its interior.
Due to the condensation of atmospheric moisture, water is deposited on the wall, floor, and ceiling, which may cause dampness.
Other Miscellaneous Causes Of Dampness.
Moisture also enters the structure due to the following causes:
- Poor drainage at the building.
- Improper orientation of walls.
- Improper slope of roof.
- Poor construction, etc.
Effects Of Dampness In Building Structure
Following are the ill effects due to entry of dampness in a structure:
- It gives rise to the breeding of mosquitoes and creates an unhealthy environment, which eventually results in ill health of the people living in the building and the surrounding areas.
- Transportation of water through walls causes patches on the wall.
- The decorations on the wall are damaged due to dampness.
- The presence of moisture causes efflorescence in walls, which disintegrates bricks, stones, tiles, etc.
- The presence of moisture causes rust in reinforcement steel bars, eventually reducing the strength of the structure.
- Wooden furniture and components like doors and windows may get damaged when moisture comes in contact with it.
- When moisture comes in contact with the electrical fittings, electricity leakage may take place, resulting in a short circuit.
How To Prevent Dampness In Buildings
Prevention of dampness in a structure can be done by damp proofing. Damp proof course prevents the entry of moisture into the building. Damp proofing can be done using several methods.
Below given are the methods for damp proofing a building:
- Use of damp proof course (DPC): membrane damp proofing.
- Integral damp proofing.
- Surface treatment.
- Cavity wall construction.
- Pressure grouting.
1. Use Of Damp Proof Course (DPC): Membrane Damp Proofing
This method consists of introducing a water-resistant membrane or a damp-proof course (DPC) between the source of moisture or dampness and the part of the structure adjacent to it.
The damp-proof course may include some flexible materials like bitumen, mastic asphalt, bituminous felt, plastic or polythene sheets, metal sheets, cement concrete, etc. The damp proof course can be applied either horizontally or vertically in floors, walls, etc. which are prone to damage by dampness.
While providing damp proof course, some specific principles should be followed, which are given below:-
– It should cover the full surface of wall, including the wall’s thickness, excluding rendering.
– The layer of mortar supporting the damp proof course should be properly and evenly leveled. It should also be free from projections so that the DPC is not damaged.
– Damp proof course shall be laid in such a way that a continuous projection is provided and maintained.
– A continuous DPC should be laid horizontally, at junctions and corners of the walls.
– When a horizontal damp proof course is continued to a vertical face, a cement concrete fillet of approximately 7.5 mm radius shall be provided at the junction.
– The damp proof course shouldn’t be kept exposed on the surface of the wall. Due to such exposure, damp proof course may get damaged during the finishing work.
2. Integral Damp Proofing
Integral damp proofing is a method in which a mixture of concrete and certain waterproofing compounds is applied to the aﬀected area of the structure.
This mixture when applied to the surface of the structure forms an impermeable layer, which does not allow the moisture to enter the building or the structure. These compounds are available in three forms. They are as follows:
– Compounds made from chalk, talc, etc. may fill up the concrete voids under mechanical action principle.
– Compounds like alkaline silicates, aluminum sulfate, calcium chlorides, etc. react with the concrete to form waterproof concrete.
– Compounds like soap, petroleum, oils, and fatty acids like sodium ammonia work on the water repulsion principle. When such compounds are mixed with concrete, it results in the formation of water-repellent concrete.
3. Surface Treatment
In this method, a layer of water-repellent compounds is applied on the aﬀected surface through which the moisture enters the structure.
For surface treatment, water-repellent compounds like metallic soaps such as calcium and aluminum plates and stearates are highly eﬀective.
It should be noted that surface treatment for dampness is eﬀective only when the moisture is on the surface of the structure and not under pressure. Even the surface of exposed brick or stone walls shall be sprayed with water-repellent compounds if required.
4. Cavity Wall Construction
Cavity wall construction is an eﬀective method for preventing dampness. In this method, the primary wall of a building is shielded by an outer skin wall, leaving a cavity or a little gap between the two.
The cement mortar used for guniting consists of cement and sand in the ratio of 1 part of cement to 3 parts of sand. This mixture of cement and sand is shot on the cleaned surface using a cement gun under a pressure of 2 to 3 kg per centimeter square.
The nozzle of the equipment is kept at a distance of 75 cm to 90 cm from the surface. The mortar mix, once applied, should be cured for at least 10 days to achieve maximum strength.
6. Pressure Grouting
Pressure grouting is a method in which the cement grout is forced into the cracks, voids, and fissures in the structure or a building under pressure. The components of a structure that are prone to moisture penetration are consolidated and are made resistant to water penetration.
This method is quite eﬀective and gives good and eﬀective results. Pressure grouting can be used for cracks of various sizes and lengths and also for various depths.
Materials Used For Damp-proofing
Various materials used for damp proofing are as follows:-
- Hot bitumen
- Mastic asphalt
- Bituminous or asphaltic felt
- Metal sheet
- Combination of bituminous felt and sheet
- Cement concrete, and
- Plastic sheets