What Is Dampness?
The most common source of dampness is due to the capillary attraction of sub-soil water in the foundation and walls of the building. Water can penetrate the masonry through faulty sills, bad workmanship, etc. and hence in buildings, a layer of water repellent material called damp proof course (DPC) is introduced, which acts as a barrier against the capillary rise of water.
Requirements of an Ideal Material for Damp-Proofing
Following are the requirements of an ideal material for damp-proofing:
- Damp Proofing material should be durable.
- It material should be dimensionally stable.
- Material should be reasonably cheap.
- The material should be free from sulfates, chlorides, and nitrates.
- The material should be such that it remains steady and does not allow any movement n itself.
- The material should be perfectly impervious.
- The material should be capable of resisting safely the loads coming on it.
- The material should be flexible so that it can adjust the structural movements without any fracture.
Materials Used for Damp-Proofing
Following are the materials which are commonly used for the damp-proofing:
- Hot Bitumen
- Mastic Asphalt
- Bituminous Felts
- Metal Sheets
- Combination of Sheets and Felts
- Stones
- Bricks
- Mortar The mortar
- Cement Concrete
- Plastic Sheets
1. Hot Bitumen
This is a flexible material and is placed on the bed of concrete or mortar. This material should be applied with a minimum thickness of 3 mm.
2. Mastic Asphalt
This is a semi-rigid material, and it forms an excellent impervious layer for damp-proofing. The asphalt is a very durable and completely impervious material. It can withstand only very slight distortion. It is liable to squeeze out in very hot climates or under very heavy pressure.
3. Bituminous Felts
This is a flexible material. It is easy to lay and is available n rolls of normal wall width. It is laid on a layer of cement mortar. An overlap of 100 mm is provided at the joints, and full overlap is provided at all corners. The laps may be sealed with bitumen, if necessary.
The bitumen felt can accommodate slight movements. But it is liable to squeeze out under heavy pressure, and it offers little resistance to sliding. The material is available in rolls, and it should be carefully unrolled, especially in cold weather.
4. Metal Sheets
The sheets of lead, copper, and aluminum can be used as the membranes of damp-proofing. The lead is a flexible material. The thickness of lead sheets should be such that its weight is not less than 200 N/m2. The lead can be dressed to complex shapes without fracture, and it possessed high resistance to sliding action.
It is impervious to moisture, and it does not squeeze out under ordinary pressure. It resists ordinary atmospheric corrosion. The surfaces of lead coming in contact by a coating of bitumen or of bitumen paint of high consistency. The copper is a flexible material.
It possesses a higher tensile strength than that of lead. It is impervious to moisture, and it does not squeeze out under ordinary pressure. It possesses high resistance to sliding action. The external walls, especially of stones, are likely to be stained when a damp-proof course of copper is adopted.
The surface of copper coming Ja contact with mortars are likely to be affected. But, for normal use, the metal does not require any protective coating. The aluminum sheets can also be used for damp-proofing. But they should be protected with a layer of bitumen.
5. Combination of Sheets and Felts
A lead foil is sandwiched between asphalt or bituminous felt. This is known as the lead core, and it is found to be economical, durable, and efficient.
6. Stones
The two courses of sound and dense stones such as granites, slates, etc. laid in cement mortar with vertical breaking joints can work as an effective damp-proofing course. The stones should extend for full width of the wall. Sometimes the stones can be fixed as in case of a roof surface, on the exposed faces of the wall, etc.
7. Bricks
The dense bricks are absorbing water less than 4.50% of their weight, can be used for damp-proofing at places where the dampness is not excessive. The joints are kept open. Such bricks are widely used when a damp-proofing course is to be inserted in an existing wall.
8. Mortar
The mortar to be used for bedding layers can be prepared by mixing 1 part of cement and 3 parts of sand by volume. A small quantity of lime is added to increase the workability. For plastering work, the water-proof mortar can be prepared. It is prepared by mixing 1 part of cement, 2 part of sand and pulverized alum at the rate of 120 N / m3 of sand.
In the water to be used, 0.75 N of soft soap is dissolved per liter of water, and this soap water is then added to the dry mix. The mortar thus prepared is used to plaster the surface. Alternatively, some patented water-proofing material such as Pudlo, Cido, Dempro, etc. may be added to the cement mortar.
9. Cement Concrete
A cement concrete layer in the proportion 1: 2: 4 is generally provided at the plinth level to work as a damp-proofing course. The depth of cement concrete layer varies from 40 mm to 150 mm. It stops the rise of water by capillary action, and it is found to be effective at places where the dampness is not excessive.
10. Plastic Sheets
The material is made of black polythene, having a thickness of about 0.50 mm to 1 mm with the usual width of wall, and it is available in roll lengths of 30 m. this treatment is relatively cheap, but it is not permanent.
FAQ on Damp Proofing
What Is Damp Proofing?
Damp proofing is a method used to prevent moisture from penetrating and causing damage to buildings. It typically involves the installation of a barrier, known as a damp proof course (DPC), to stop water from rising through the walls and foundation due to capillary action.
Why Is Damp Proofing Important?
Damp proofing is crucial for protecting a building from moisture-related problems such as mold growth, deterioration of structural materials, and compromised indoor air quality. Effective damp proofing helps maintain the structural integrity and longevity of a building.
What Are the Common Sources of Dampness in Buildings?
Common sources of dampness include capillary rise of sub-soil water, faulty sills, poor workmanship, and water penetration through walls due to inadequate or damaged damp proof courses.
What Are the Key Requirements of an Ideal Damp Proofing Material?
An ideal damp proofing material should be durable, dimensionally stable, affordable, free from sulfates, chlorides, and nitrates, impervious to moisture, capable of withstanding loads, and flexible enough to accommodate structural movements without cracking.
What Materials Are Commonly Used for Damp Proofing?
Common damp proofing materials include hot bitumen, mastic asphalt, bituminous felts, metal sheets (such as lead, copper, and aluminum), combinations of sheets and felts, stones, bricks, mortar, cement concrete, and plastic sheets.
How Is Hot Bitumen Used in Damp Proofing?
Hot bitumen is a flexible material applied in a minimum thickness of 3 mm on a bed of concrete or mortar. It acts as a barrier to prevent moisture from rising through walls and foundations.
What Are the Advantages of Using Mastic Asphalt for Damp Proofing?
Mastic asphalt forms an excellent impervious layer and is very durable. It can withstand slight distortions but may squeeze out under high pressure or in very hot climates.
Can Metal Sheets Be Used for Damp Proofing?
Yes, metal sheets like lead, copper, and aluminum can be used. Lead is flexible and resistant to moisture but requires protection from corrosion. Copper and aluminum are also effective, with copper needing less protective coating and aluminum often being coated with bitumen.
What Is the Purpose of Combining Sheets and Felts in Damp Proofing?
Combining sheets and felts, such as a lead foil sandwiched between asphalt or bituminous felt, enhances durability and efficiency, providing a cost-effective and reliable damp proofing solution.
How Do Bricks and Stones Function in Damp Proofing?
Dense bricks and stones, when laid with open joints and cement mortar, can serve as effective damp proofing courses. They are used especially in cases where dampness is not severe.
What Is the Role of Cement Concrete in Damp Proofing?
Cement concrete layers, typically in a 1:2:4 proportion, are used at the plinth level to prevent capillary rise of water. This method is effective in areas with moderate dampness.
Are Plastic Sheets a Good Option for Damp Proofing?
Plastic sheets made of black polythene are relatively cheap and easy to install but are not considered permanent solutions. They may be suitable for temporary applications or where other methods are not feasible.
How Can I Determine Which Damp Proofing Material to Use?
The choice of damp proofing material depends on factors such as the level of moisture exposure, budget, ease of installation, and the structural requirements of the building. Consulting with a construction professional can help in selecting the most appropriate material.
