Damp proofing, or damp-proof construction, is a construction technique that aims at walls and floors to prevent moisture from passing into the interior spaces. It is generally applied at basement levels, which restricts the movement of moisture through walls and floors.
Generally, damp proofing is required in areas where a highwater table or other severe soil-water conditions are known to exist. In areas without high soil hydrostatic pressure, damp proofing used in conjunction with proper drainage and lawn grading is sufficient and provides long-lasting protection.
Usually, a coating that is either sprayed on or rolled onto the outside of the wall achieves damp proofing. Rising damp, which occurs when water from the earth seeps into the foundation, is shielded by a damp proof course. When added to the concrete mixture, damp proofing can also be crucial in making the concrete itself water resistant.
Why is damp proofing important?
Keep mould and mildew at bay in your home
Mould, mildew, and bacteria growth in wet, damp walls, floors, or ceilings are definite triggers for people suffering from asthma, bronchitis, or other lung and breathing issues. Damp proofing ensures that your walls resist this moisture hazard so that your family can stay safe and healthy, breathing freely. When condensation builds up inside your walls, or water is allowed to sit without sufficient ventilation, mildew and bacteria begin to grow. Damp proofing can help eliminate this problem.
It keeps walls strong
Dampness can affect walls by seeping into the walls, which can further destroy wall paint, furniture, and ceilings. Water can gradually affect the strength of a building structure, thus damp proofing is important to keep the structure strong and long-lasting.
The difference between damp-proofing and waterproofing
Damp proofing is just a coating that is either sprayed on or hand applied to the outside of the wall. On the other hand, waterproofing is the treatment of the surface to prevent the passage of liquid water in the presence of hydrostatic pressure.
Methods of damp proofing
- Membrane Damp-Proofing
A water repellent material or damp proof course(D.P.C.) is introduced in between the source of dampness and the part of the building adjacent to it. The damp proofing course may consist of flexible materials such as bitumen, mastic asphalt, bituminous felts, plastic or polythene sheets, metal sheets, or cement concrete. Damp proofing courses may be provided either horizontally or vertically on floors, walls, etc. Provision of a damp-proofing course in the basement is normally termed as “tanking”.
- Integral Damp Proofing
In this type of damp proofing, certain materials are mixed with concrete. Compounds made from chalk, talc, and fuller’s earth may fill the voids of concrete under the mechanical action principle. Alkaline silicates, aluminium sulfate, calcium chlorides, and other compounds react chemically with 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. Commercially available compounds like Publo, Permo, and Silka, etc. are mixed with concrete for damp proofing.
- Cavity Wall Construction
Cavity wall construction is an effective method of damp prevention. In this method, the main wall of a building is shielded by an outer skin wall, leaving a cavity between the two. The cavity prevents the moisture from travelling from the outer to the inner wall.
- Pressure Grouting
This method consists of forcing cement grout under pressure into cracks, voids, fissures, and so on present in the structural components of the building or in the ground. Thus, the structural components and the foundations, which are liable to moisture penetration, are consolidated and are thus made water penetration-resistant. This method is quite effective in controlling the seepage of raised ground water through the foundation.
- Surface Treatment
Moisture finds its way through the pores of material used in finishing. In order to check the entry of the moisture into the pores, they must be filled up. In the surface treatment method, a layer of water repellent substances or compounds is applied on these surfaces through which moisture enters. The use of water repellent metallic soaps such as calcium and aluminium oleates and stearates is much more effective against rain water penetration.
In this method of damp proofing, an impervious layer of rich cement mortar is deposited under pressure over the exposed surfaces for water proofing or over pipes, cisterns, etc. for resisting the water pressure. The operation is carried out by the use of a machine known as a “cement gun.
The cement gun consists of a machine having arrangements for mixing materials and a compressor for forcing the mixture under pressure through a 50 mm dia. flexible hose pipe. The hose pipe has a nozzle at its free end to which water is supplied under pressure through a separate connection.
Materials used for damp proofing
- Bitumen Mastic (Mastic Asphalt): It consists of asphalt or bitumen mixed with fine sand in a hot state to form an impervious mass. Due to this consistency, it can be spread (when hot) to a depth of 2.5cm to 5cm, which sets on cooling.
- Hot Bitumen: It consists of a 6 mm thick sheet of bitumen prepared in rolls having a width equal to that of a brick wall.
- Metal Sheets: metals such as aluminium, copper or lead are used throughout the thickness of the wall.
- Stone Slabs: Two layers of stone slabs or slates laid in lime, cement and sand mortar (1:1:6) make the best DPC.
Furthermore, damp proofing can save you from a plot of repair work in the future, removing the tension of yearly renovation. As it is believed “prevention is better than cure”, damp proofing is the precaution that everyone should take during construction.