There are various methods of damp proofing in the building. before directly come on the point we will discuss dampness and what is damp proofing. Dampness problem is very common in any building. If proper care is not taken to eliminate that, it becomes a serious issue for spoiling the appearance as well as structural stability.
What is damp Proofing?
Damp proofing is methods or treatments used to prevent dampness to enter through walls or floors into the interior property of the building.
Dampness can be seen in much property, especially older properties which may have been constructed without a damp-proof membrane. But some of the new properties also experience this problem because of water leakage, heavy rainfall, change of temperature, etc.
Causes of Dampness in buildings
- Heavy rain smashing
- Low level of site
- Drainability of soil
- Atmospheric condition
- The defective orientation of the building
- Moisture entrapped during construction
- Defective construction e.g. joints
- Use of poor quality bricks which ultimately absorb a lot of water.
- Use of Poor quality of concrete (permeable concrete)
Effect of dampness:
- It causes Musty smell & Damp and
- Mildew or mould o forming on walls
- It causes Peeling wallpaper, Staining of wall coverings, & blistering paint
- Damp walls & dark patches
- Fragmenting plaster & Discoloration
- It leads to Decay of timber by wood-rotting fungi or presence of wood-boring weevils
- Dampness symptoms visible on skirting boards, where nails or screws show signs of rust
- It develops rusting on angle beads within damp plasterwork
- It causes the appearance of salt stains on outside walls
- Cement plaster mortar on the outside of the property begins to crumble away
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Methods of Damp proofing
Method of damp proofing
1. Membrane Damp Proofing:
In this method, a water resistance membrane or damp proof course (D.P.C.) is introduced in between the source of dampness and the part of the building adjacent to it. DPC may consist of flexible materials such as bitumen, mastic asphalt, bituminous felts, plastic or polythene sheets, metal sheets, cement concrete.
The DPC can be introduced or placed either horizontally or vertically in floors, walls, etc. Damp Proofing Course provided basement is normally termed as ‘Tanking’.
The following point should be kept in mind while providing waterproof course:
- The DPC should cover the full thickness of walls, excluding rendering.
- The mortar used for DPC should be leveled and even, and should be free from projections so that damp proof course is not damaged.
- DPC should be laid in such a way that a continuous projection is provided.
- While providing DPC at junctions and corners of walls, the horizontal damp proof course should be laid continuous.
- When horizontal DPC is continued to a vertical face, a cement concrete fillet of 7.5 cm radius should be provided at the junction.
- Continuous correct relation should be maintained between two damp proof courses, to ensure a complete and continuous barrier to the passage of water from floors, walls or roof.
- Care taken that no damp proof course left out of wall surface; otherwise, it can get damaged during wall finishing.
Damp Proof Membrane Cost: Rs. 80 / Kilogram
2. Internal Damp Proofing:
In this method of damp proofing, some waterproofing compounds are added to the concrete mix, so that it becomes impermeable. Following are some waterproofing compounds maybe use for internal damp proofing. Compounds made from chalk, talc, fullers earth, which may fill the voids of concrete under the mechanical action principle.
Compounds like alkaline silicates, aluminum sulphate, calcium chlorides, etc. This compound chemically reacts with the concrete to produce water proof concrete.
Compounds like soap, petroleum, oils, fatty acid compounds such as stearates of calcium, sodium, ammonia, etc. work on water repulsion principle. When this compound mixed with a mix, concrete becomes water resistance.
Commercially available compounds like Publo, Permo, and Silka, etc.
The amount of chemical compound added to cement is depends upon the manufacturer’s recommendations. For general waterproofing work 1 kg of chemical compound per one bag of cement to render the mortar or concrete waterproof.
Methods of Damp Proofing
3. Surface Treatment:
In the internal finish, dampness finds its way through the pores of material used in finishing. To prevent the entry of the moisture into the pores, they must be filled up. To limit the entry of moisture in surface finish a layer of water repellent substances or compounds are applied on these surfaces through which moisture enters.
The use of waterproof metallic soaps such as calcium and aluminum stearates (Stearates are the salts and esters of stearic acid)are much effective against rainwater penetration. The finishing of outer work such as Pointing and plastering surfaces must be done carefully, using waterproofing agents like sodium or potassium silicates, aluminum or zinc sulphates, barium hydroxide and magnesium sulphates, etc. This method of treatment is effective only when the moisture occurring on the surface and is not under pressure.
For exposed stone or brick wall face may be treated by spraying with water repellent solutions. For external wall plastering use of mix proportion of cement, lime, and sand mixed in 1:1:6 is found to serve the purpose of preventing dampness in the wall due to rain effectively.
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4. Cavity wall construction:
The method of Cavity wall construction is an effective method of damp prevention. In this the main external wall is shielded by an outer skin wall, leaving a cavity between the two. The cavity leaves a gap between walls which prevents the moisture from traveling from the outer to the inner wall.
In Guniting, the exposed damp surface is cover with an impervious layer of rich cement mortar is deposited under pressure over the exposed surfaces for waterproofing or over pipes, cisterns, etc. for resisting the water pressure.
The Guniting of mix or spraying of mix operation is carried out by use of a machine known as cement gun. In this cement gun machine having arrangements for mixing materials and a compressor for forcing the mixture under pressure through a 50 mm dia flexible hose pipe. A nozzle is fixed to the hose at its free end to which water is supplied under pressure through a separate connection.
In this method, before Guniting is done the surface to be treated is first thoroughly cleaned of dirt, dust, grease or lose particles and wetted properly. As the surface is sufficiently wet a cement mortar consists of 1: 3 cement sand mix, is shot on the cleaned surface with the help of a cement gun, under a pressure of 2 to 3 kg/cm2. The distance between the nozzle of the machine and surface to be gunited is kept at a distance of about 75 to 90 cm. The mortar used for uniting treatment should be desired consistency and thickness can be deposited to get an impervious layer. The surface should be properly cured at least for 10 days.
In this method, to ensure dense compaction and better adhesion of the rich cement mortar is applied under pressure with the help of Guniting gun and hence the treated surface becomes waterproof.
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