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WATERPROOFING TYPES & THEIR METHODS:

 

A. REVIEW OF THE OLD WATERPROOFING TYPES & THEIR METHODS:

 
 Types of waterproofing systems are as follows:
 
 1. Brick Bat Coba system or Lime Terracing
 2. Bituminous Treatment
 3. Metallic Sheet Wrapping
 4. Poly-urethane based Waterproofing treatment
 5. Epoxy Based Water proofing Treatment
 6. Box Type Water proofing System
 
 

 

1. Waterproofing Methods of 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 lightweight mortar on the roof and spreading it to give gentle slopes for draining away the rainwater immediately. The mortar consisted of lightweight 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 these systems, with neatly finished top with lines engraved on top of plastic mortar now known as IPS. Some practiced embedding broken tile or ceramic pieces in the plastic mortar and called it china mosaic. This type of system remained most popular with multi-storied construction in all major 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 entering 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.
 

2. Waterproofing Methods of Bituminous Treatment:

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 fiber glass/polypropylene mats with chemically modified bitumen. These membranes are laid 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 vapor. 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 the concrete 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.
 
Bitumen is very effective in waterproofing of basements from outside. Bitumen primers have very successfully been used as damp-proof course in earlier days. This practice is slowly discontinued for whatever reasons now very few engineers now believe that this was in practice once. As consequence of this absent DPC we have a lot of cases of rising dampness, which we tend to attribute to wrong reasons such as the quality or salinity of sand etc. Bitumen still is the product of first choice where it is commonly recommended, in areas such as industrial roof waterproofing, basement waterproofing, and damp-proof course. More over bitumen is the most economical product available for waterproofing.
 

3. Waterproofing Methods of Metallic Sheet Wrapping:

Because of 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 utilizing thick copper sheets. An extension of this practice was to try thin foils of copper and aluminum for wrapping the concrete surfaces with nagging leakage problems. Unavailability of common joining material for these metal foils and the concrete and mortar created weakness in the system at the joints. This discouraged the system in its infancy only. But there after the metal manufacturers have been trying to market this type of waterproofing system with improved adhesives as and when the metal market slumped.
 

4. Waterproofing Methods of Polyurethane based treatment:

Polyurethane 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 isocyanides such as TDI or 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 fiber glass reinforcing mats. The systems failed because coefficients of thermal expansion of concrete and rigid PU membrane being different lateral movement or creep occurred with the passage on one working climatic cycle. When exposed to ultra violet rays or direct sunlight most polyurethane rigid membranes became brittle and crumbled. Apart from this the application of polyurethane coating needed very rigorous surface preparation. The surface needed to be neutralized by removing alkalinity from the concrete surface through acid itching then washing and blowtorching to make the surface bone dry. This kind of surface preparation with acids angered the civil engineering community and the product ceased to be used as waterproofing material apart from its several failures. Never the less continuous research in the polyurethane technology gave the construction industry excellent sealant for glazing industry and foams for thermal insulations. The new generation polyurethanes, which are alkali stable and water-based, may find better applications in waterproofing industry.
 

5. Waterproofing Methods of Epoxy Based Water proofing System:

Like polyurethane is also a two-component system having a base resin and a reactor or curing agent. Base resin is obtained by dissolving Bis-phenol A flakes in epichlorohydrin. This base is available in various viscosity ranges to suit different application conditions. The curing agent is an amine/polyamine aliphatic or aromatic, or an amine-adduct for general applications and polyamide or an amino-amide for coating purposes. After mixing base and reactor components the resultant viscous liquid or paste if some fillers are added to it can be brush applied like a paint or trowel applied like a mortar.
 
Here also epoxies not withstanding the alkalinity of concrete and the concrete needs to be acid washed and neutralized, which the civil engineers hated. Here again the coefficient of thermal expansion of concrete and epoxy being different the compatibility of epoxy in waterproofing exposed concrete surfaces such as roofs became limited. Later the use of epoxy in waterproofing was discarded. But epoxies have come to stay in civil engineering industry as bonding agents, floor & wall coatings, coatings for food processing units, operation theatres and computer and pharmaceutical industries.
 

6. Waterproofing Methods for Box Type Waterproofing:

This type of water proofing system is used only for basement waterproofing or waterproofing structures below the ground level from outside to prevent leakages of subsoil water into the basement.
 
In this method limestone slabs (Shahabad Stones) are first laid in the excavated pit over blinding concrete in a staggered joint fashion to avoid the continuity of the mortar joints. The joints are effectively filled with rich mortar admixed with integral waterproofing compound and cured. Over this the raft is laid and shear/brick walls constructed. The limestone slabs are erected around the walls in a similar fashion leaving a gap of one to two inches between the external surface of the wall and the inner face of the stone surface. The joints again effectively sealed with rich admixed mortar and the same mortar is filled in the gap between the wall and the stones. This stonework is continued up to ground level. In this system the raft and the sidewalls are protected from direct exposure to sub soil water.
 
This system works on two principles of common sense. First the area exposed to subsoil water is only the area of the joint where as the whole stone is impervious to water, hence only a fraction of area, that is, that of the joint is exposed to subsoil water, when the joint itself is filled with rich and quality mortar. Secondly, the path of water to reach the raft or the sidewall is elongated. This elongated path is through quality mortar. This system seeks to delay the occurrence of leakages in the basements. A lot of building structures are waterproofed by this system. A few notable successes are to its credit especially in five star hotels and of-course there are a few failures as well.
 

B. MODERN WATERPROOFING METHODS & TECHNIQUES:

Modern technique aims to understand the functional behavior of the structure, understand the properties of the available materials arrive at a system, which is best suited for the structure and incorporate the system at the design stage only.
 
A single product or technique is not usually enough, involvement of various bodies and techniques in coordination is essential for making structures waterproof. For success of any system the building structure should have sufficient and efficient control joints if the slabs dimensions are more than twenty meter in any direction. Control joints are structural engineering design features. These joints are supposed to be designed and their configuration marked on the drawings and their detailing needs to be given with respect to waterproofing system proposed in large buildings. Different types of control joints are Construction joints or day joint, crack inducer joint, contraction joint and expansion joint. Coefficient of thermal expansion of concrete is between 6 to 10 X 10-6 mm/mm/oC. If proper control joints are not provided in large slabs, no waterproofing system works. Modern technique relies basically on two main waterproofing systems, which are fool proof and simple.
 
They are as follows:
 
 1. Crystalline waterproofing method
 2. Flexible membrane waterproofing method
 

1. Crystalline Waterproofing System & It's Method:

This system involves blocking the water bearing capillaries with insoluble crystals. This method is used for waterproofing water-retaining structures like overhead/underground water tanks, sunk slabs of bathrooms and toilets, swimming pools, basements, terrace gardens etc. The main product in this system is a grey or brown looking powder.
 
 The method of treatment involves saturating with water the surface to be treated. Then mixing two and half volume of the powder with one volume of water to form neat consistency hot slurry. This slurry is brush applied on the saturated surface. The active ingredients in the slurry pass through the water bearing capillaries and react with calcium oxide in the concrete to form insoluble crystals, which effectively block the capillaries. Further the chemical ingredients of the product remain in concrete to reactivate the process of crystallization as and when a new capillary is developed. This system of water proofing the water retaining structures is practiced in all the developed countries.
 
Typical specification for this type of system is as follows:
 
Clean the surface to remove all loose particles, grease shuttering oil and such deleterious materials to get a sound concrete surface.
Cracks if any should be cut into V shaped grooves one inch wide and one inch in depth. Cut honey combed areas back to sound concrete.
Repair these areas first by priming with crystalline waterproofing slurry and then by filling them with crystalline modified mortar produced by mixing crystalline waterproofing powder OPC and zone II sand in the proportion of 1:1:4 and water enough to produce a stiff consistence paste. Allow the repair mortar to dry.
Thoroughly sprinkle water on the area to be treated till the surface becomes saturated. Some recommend overnight pending for effective results
Prepare crystalline waterproofing slurry by mixing the powder and water in the proportion of two and half volume of powder to one volume of water to form a hot slurry. Brush apply this slurry on the water saturated surface in two coats.
When the second coat is still wet plaster the surface with 1 : 4 cement sand mortar admixed with an integral waterproofing compound and cure normally.

 

2. Flexible Membrane Waterproofing System & It's Method:

The main product used in this system comprises of two components one liquid and the other is a powder packed roughly in the proportion of 1:4 by weight. The liquid component is an acrylic emulsion and the powder component is a polymer-modified cement with film forming chemicals and fillers, and some manufacturers add reinforcing fibers to make the product extra effective.
 
When these two ingredients namely the pre-weighed powder and the liquid are mixed together an uniform slurry results. This slurry is brush applied on the roof surface, which upon drying forms a flexible film. Since there is cement in this product its compatibility with concrete is excellent. The film further allows the breathing of the concrete without any hindrance hence there is no problems of its de-lamination from the concrete surface. This film being flexible takes care of the deflections in the slab and the movements caused because of primary or secondary settlements, movements due to wind loads and temperature stresses developed in the concrete. This system can be used on surfaces, which had bituminous treatment earlier. In European countries this type of product is used as coating on pre-stressed concrete bridge girders to protect them from aggressive chemical atmosphere. A typical waterproofing specification using flexible membrane system will be as follows:
 
Clean the surface to remove all loose particles, grease shuttering oil and such deleterious materials to get a sound concrete surface.
Cracks if any should be cut into V shaped grooves one inch wide and one inch in depth. Cut honey combed areas back to sound concrete.
Repair these areas with a stiff paste of fiber reinforced polymer repair mortar generally sold in the name of crack fill.
Mix the powder and the liquid components of the product to form an uniform slurry and brush apply this slurry on the surface to be waterproofed.
When the waterproofing coating is still tacky apply 1 : 4 cement sand screed and cure normally.
 

 

Copyright 2014 R.K.Interiors. The content is copyrighted to Manoj Sharma and may not be reproduced on other websites