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The occurrence of excessive dampness in buildings, especially those of concrete and masonry, is widespread and reflects upon the quality of building materials and construction techniques. The defect is long-standing and the cause of extensive deterioration of the material. Dampness affects the aesthetics and the structural integrity of buildings and may render them uninhabitable.
Dampness in a structure is due to the presence of moisture in different parts such as the flooring, wall, roofing system, etc. Dampness gives rise to unhygienic conditions, therefore, extra care should be taken to prevent such situations. This article discusses the materials needed for preventing dampness and the techniques required to prevent moisture penetration.
Contents:
1. Reasons for Dampness
Generally, moisture penetration in a structure may occur due to:
- Groundwater movement
- Heavy rainstorm
- Leakages from pipelines
1.1 Dampness due to Groundwater
The foundation of any structure is constructed either on soils or rocks. Nevertheless, the foundation may come in contact with groundwater due to an increased groundwater level. But the major cause is moisture penetrating the structure from the ground due to capillary action.
1.2 Due to Heavy Rainstorm
Rainwater may seep into the different parts of the structure which are mentioned below:
1.2.1 From Top of the Wall
If the top of the wall is not safeguarded with an impervious course like concrete, then water can penetrate into the wall and keep it damp for a very long time.
1.2.2 From External Walls
Undoubtedly, the external walls are the primary contact of rainwater. Thus, the moisture can penetrate the wall due to the splashing of the external wall by rainwater. The most important factor is a poor plaster coat on external walls which is the primary source for this type of dampness.
1.2.3 Inappropriate Positioning of Pipelines
A thin layer of water stagnates near the mouth of pipelines if the roofing pipelines are not correctly positioned. As a result, the water enters into the roofing system and the walls.
1.2.4 Due to Incorrect Roofing Slopes
The most important cause of moisture penetration in a roofing system is flat roofing. Water ponds are formed if an effective slope is not provided. Thus, moisture can enter into slabs and the dampness may prevail if water remains for a longer period in the slabs.
1.2.5 Malfunctions During Construction
Moisture can penetrate into the structures due to imperfect wall joints, incorrect slopes to chejja, and construction joints in the roofing system, etc.
1.3 Due to Leakages from Pipelines
Basically, in a structure consisting of overhead tanks, pipelines are taken over roofs and along the wall. Generally, water leaks through the pipeline joints and penetrates into the structural elements. In such situations, dampness may prevail in the structural elements.
2. Effects of Dampness
Dampness in a structure prevails due to moisture penetration into the structural elements. Thus, it can affect the functioning of the structural elements. The effects of dampness are discussed below:
1. The structure appears unpleasant due to the formation of patches on the structural elements.
2. Bleaching and flaking of the paints may happen, which may further result in the formation of colored patches on the walls and ceilings.
3. Effectiveness of plaster reduces.
4. Disintegration of stones and bricks.
5. Steel in the slabs and beams begins to rust. Thus, the life span of the structure decreases.
6. Electric short circuits may occur due to water ingress in electrical fixtures.
7. Flooring system may get destabilized.
8. Damage to flooring covers.
9. Wooden parts of structures like door frames and cabinets may warp.
10. Dry decomposing of wood.
11. Dampness promotes the growth of termites which may cause damage to wooden elements.
12. Breeding of mosquitoes.
13. Darkness and heat may generate many types of bacteria thus, increasing the chances of bacterial infections.
3. Requirements of Damp Proofing Materials
Damp proofing materials are required to reduce the ill-effects of dampness. The requirements of an ideal material for damp proofing are discussed below:
- It must be impervious.
- It must be versatile.
- Material should be compatible for performing leakage-proofing of joints.
- It should be stable.
- It must be durable and should have a life equal to the building.
- It should safely withstand the loading.
- Material should not consist of sulphates, chloride, and nitrates.
- It should not be expensive.
4. Materials Used for Damp Proofing
Various types of materials are available in the market for damp proofing. These materials are discussed below:
4.1 Bitumen
Generally, bitumen works in hot weather conditions. It is incredibly versatile and can be applied with a brush to the bedding of mortar or concrete. For effective results, the density of the bitumen coat should be at least 3 mm.
4.2 Mastic Asphalt
Mastic asphalt is a semi-rigid product. It is acquired by heating asphalt with sand and mineral fillers. It is completely impervious and therefore should be laid very carefully.
4.3 Bituminous or Asphaltic Felt
Generally, such materials are readily available in rolls. These rolls can be applied on roofing or flooring with an overlap of 100 mm on both sides. However, this material does not withstand heavy moments.
4.4 Bricks
Good bricks with water absorption less than 5% are often used to make damp proof courses. Two to four courses of bricks should be placed with cement mortar for effective results.
4.5 Stones
Stones like granite, trap and slate can be used as a damp proof course. These stones should be placed over the full width of the wall.
4.6 Mortar
Cement mortar of proportion 1: 3 with a little amount of lime and waterproofing agents are useful in making a waterproofing course. This course can be applied to foundation, flooring system, and top of parapet walls. It can also be useful for plastering the external walls.
4.7 Concrete
To reduce the risk of moisture penetration into walls, a course of 75 mm to 100 mm cement concrete (1: 1: 3 or 1: 2: 4) is provided prior to construction of walls. These courses can be placed with hot bitumen paint as an extra safety measure.
4.8 Metal sheets
Aluminum, copper, and lead sheets can be used to seal the construction joints and a bituminous seal should be provided over these sheets as an extra safety measure.
4.9 Plastic Sheets
Plastic sheets are an excellent course for damp proofing. They consist of black polythene of thickness of around 1 mm. Such plastic sheets can be used in flooring systems.
5. Techniques Required for Damp Proofing
Dampness can be prevented by designing the buildings with the right techniques. Different damp-proof techniques are discussed below:
- Damp-proof course
- Cavity walls
- Surface area treatment
- Integral treatment
- Guniting
5.1 Damp-Proof Course (DPC)
In this method, a damp proof course is provided between the source of dampness and the structural component. The DPC should be provided with any water-repellent material like bitumen, mastic asphalt, cement concrete, and metal or plastic sheets.
DPC should cover full width of the wall. Joints of DPC should be minimum and should not be at critical points.
5.2 Cavity Walls
The function of the cavity wall is to protect the main wall of the building from rainwater. By providing a cavity wall, the resistance to moisture penetration into the main load-bearing walls increases. The cavity wall will act as a shield for the masonry wall.
Cavity wall has two main components, i.e. exterior wall and interior wall. The exterior wall acts as a non-load bearing wall, whereas the interior wall acts as a load-bearing wall. Exterior wall reduces the risk of moisture penetration into the interior wall and serves as a protective layer to the interior elements.
5.3 Surface Area Treatment
This method is only useful when the dampness is shallow and not under pressure. It consists of an application of a layer of water-repellent compounds on the surface area. Basically, most of the water proofing materials have silicates of salt or potassium and sulphates of zinc, magnesium, and aluminium. Therefore, such water-repellent compounds should be applied only on external surfaces.
5.4 Integral Treatment
In this technique, readily available substances are mixed with concrete prior to the concrete wet mixing. Consequently, this concrete should be used in making the damp proof course.
Such readily available substances are chalk, talc, flutter earth, or chemical substances like calcium chloride, aluminum sulphate, etc. Some substances also consist of compounds like soap, petroleum oils, fatty acids, etc.
5.5 Guniting
In this method, a mix of cement and water is filled in a cement gun, which is used to apply the mixture on the surfaces to make them water-resistant. In addition, 1: 3 or 1: 4 cement mortar should be applied to the surface with pressure using compressed air for providing an impervious layer of mortar.
FAQs
Damp proofing is a treatment provided to prevent moisture penetration into the structure through walls or floors.
Firstly, the cracks in the walls should be sealed. After that, apply waterproofing agents on the external wall and provide a damp proofing course. In addition, guniting can be done over damp proofing course to create an impervious layer of mortar so that moisture penetration can be completely avoided.
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