Posted by Admin on March, 28, 2013
Waterproofing of building to prevent the ingress of water is an activity, which, perhaps is practiced in one way or the other, ever since the first building was built on earth. The methodology has been changing with the changes in the architectural designs and with the availability different building materials in construction. In the initial stages when stone was the main building construction material placed in position with mud or lime mortar the emphasis used to be to make the construction in such a way that the rain water does not collect on the roofs. Hence old architecture relied mainly on dome or slanting structures for the roofs. The slow speed of such construction and unaffordability of common man to build such structures for their own dwelling, made constant evolution and development in the construction material technology. With these developments the concepts of waterproofing also changed. Now in present day construction wherein the ordinary portland cement and its blends with puzzolonic and slag materials has come to stay a lot of alternatives are available for a builder to choose from various waterproofing systems which are compatible with the cement. There are some compounds, which are used in plastic concrete to make it less permeable to water. These compounds are known as integral waterproofing compounds. They are based on air-entrainment or water repellence principles. These are used as a good waterproofing precautions. This subject will require in depth discussion hence will not be taken up here. Similarly there are some water proofing techniques for vertical surfaces. These techniques are used also used for preserving heritage buildings by stopping/minimising the aging process of these buildings. This subject also will not be discussed here. Some of the well known water proofing systems are as follows:
Brick Bat Coba System
This system was developed during the initial stages of flat roof construction with lime mortar burnt clay brick pieces. This system involved laying of light weight mortar on the roof and spreading it to give gentle slopes for draining away the rain water immediately. The mortar consisted of light-weight brick pieces as aggregates and ground brick with lime as binding matrix. During British rule this system became more popular not because of its waterproofing efficiency but because of its efficiency in keeping the interiors cool. Some applicators developed better skills in laying this systems with neatly finished top with lines marked on top now known as IPS or with pieces of broken tiles and other ceramoic materials embedded known china mosaic. This type of system remained most popular with multi-storeyed construction in all major metro cities. The system lasts up to 15 years if done by skilful applicators. This system may be considered more from its weather proofing abilities rather than its waterproofing qualities. Once water starts going into the brickbat coba the brick pieces absorb too much of water and the roof becomes an invisible pond of water continuously causing leakage and increasing burden on the roof slab. It will be highly beneficial if brick-bat coba is laid on a flexible waterproofing membrane as water proofing as well as economical weather proofing can be achieved with this system.
Discovery of petroleum and its products and by-products has given the construction industry an indispensable product in the form of bitumen.Bitumen is more commonly used in the form of felt or flexible membrane formed by sandwiching jute fabric or fibreglass/polypropylene mats with chemically modified bitumen. These membranes are layed on the roofing over a bitumen primer. There are two types of membranes one is cold applied and the other hot applied which means one needs to heat the edges of the felt with a torch so that they melt and stick to the second layer in the overlap area. On the RCC flat roofs the bitumen felts have not been successful because of the unacceptable black appearance and inaccessibility of the terrace for other social uses. Technically it is not preferred because bitumen layer or felt on the terrace not only makes it watertight but also airtight. Concrete has the breathing property. It takes water/moisture and breathes out water vapour. Hindrance of this breathing property of concrete develops pore pressure, which causes blisters in the felt. After a few seasons the blisters multiply and eventually delaminate the felt from the concrete surface. Hindrance of breathing property of concrete makes it weak. But on the asbestos cement sheets and zinc sheets in factory roofs this bitumen felt is the only dependable waterproofing system. Hence all factory roofs in India adopt this water proofing system. Apart from this in waterproofing of basements from outside is very effective with bitumen felts. Bitumen primers have very successfully been used as damp-proof course in earlier days. This practice is slowly discontinued and we have a lot of cases of rising dampness, which we tend to attribute to the quality of sand.
Metallic Sheet Wrapping
The non-existence of suitable expansion joint filling compounds before the discovery of poly-sulphides, a complex procedure used to be adopted to treat expansion joints in concrete dams and such huge structures utilising copper sheets. An extension of that found thin copper foils and aluminium foils being used in the buildings for water proofing purposes. The absence of common joining material for metal and concrete and the weakness of the system at the joints discouraged this practice in its infancy only.
Poly-urethane based water proofing Treatment
Poly-urethane consists of two liquid components one is called the Base component and the other is called reactor or curing agent. Base is a polyol and the reactor is an isocyanide such as TDI MDI. There are various grades of polyols and so also there are numerous isocyanides. The combination of these two ingredients results in a formation liquid applied rigid membrane or a foam depending upon the selection. In water proofing this rigid liquid membrane was tried with fibreglass reinforcing mats. The systems failed because coefficients of thermal expansion of concrete and rigid PU membrane being different lateral movement or creep occurred. In UV exposure most rigid membranes became brittle and crumbled. Apart from this the application of poly-urethane coating needed very rigorous surface preparation. The surface needed to be neutralized by removing alkalinity from the concrete surface by acid itching then washing and blowtorching to make the surface bone dry. This kind of surface preparation angered the civil engineering community and the product ceased to be used as waterproofing material. Never the less continuous research in the poly-urethane gave the construction industry excellent sealant for glazing industry and foams for thermal insulations.
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