Thursday, September 8, 2011

WATERPROOFING SYSTEMS IN USE

There are various approaches to the waterproofing of a structure. Almost all of them seek to isolate the areas that are leaking from the water source by using some type of film, membrane, cementatious layer or stone layer as an intermediate layer. Some of the known methods in use are as below-

Tarfelt
Brick bat coba
Guniting
Stone waterproofing

Coatings
Integral waterproofing

Tar felt

The system is probably the oldest in practice and uses layers of tar interspersed with various forms of reinforcements to hold the layer together and prevent cracking to provide impermeable layer between the water and the surface to be protected. Depending on the number of layers used it is variously categorized as three later, five layer or seven layer tar felting treatment. Actually in a new job seven coat system is always reccomended but seldom executed since in terms of cost it turns out to be as costly as the other treatments which are technically more advanced. Most applicators use three-layer system for terrace waterproofing though ideally it is only a repair system.

Tar felting though once universally used is found to be inadequate even for the primary function for which it is designed i.e. terrace waterproofing.

Disadvantage

  1. TAR OIL DISINTEGRATES
    The tar oil that is the binder in the system disintegrates on contact with both 'UV' radiation and aggressive chemicals in subsoil water and then this leads to biodegradation of hessian reinforcement leading to collapse of the system.

  2. AIR POCKETS ARE FORMED
    The specification clearly states that a light roller should be used on top of the tarfelt so that air pockets are eliminated. This is never done and so the air pockets remain in the system and the air expands and contracts with every heating cooling cycle leading to stress on the reinforcement and ultimately they burst leading to water ingress.

  3. CHANNELS ARE FORMED WITHIN SYSTEM
    A typical problem is that since the adherence to the surface is never complete channels get formed below the tarfelting and water which enters from one place travels though these and exits wherever it finds a weak point in the concrete. Repairs if any in tarfelt have to be carried out at points sometimes far away from the point that leaks and this is hard to identify.

Modification of System
Substituting glass fiber felt instead of the hessian felt has been tried. Torching membranes which are welded on to the surface have also been introduced but have not found much common acceptance since the same are difficult to apply and also expensive.

Verdict

The only place where we have found tarfelt must be used is when waterproofing of A/c sheet roofing where the movement is so much and the joints are so large that nothing else covers them as well as a membrane based system for which the tarfelting is the cheapest. If necessary this may be overcoated with tar every year to make it last longer. Everywhere else the system is on the way out.

Brick bat coba

This is a system used particularly for roofs in the coastal region and consists of putting brickbat on roofs to give a slope and then grouting the same with mortar admixed with various proprietary chemicals most in the nature of water proofing compounds. This is mostly finished with IPS topping with a tile pattern cut into the top to form crack inducer joints to prevent cracks from appearing. This has the advantage of providing an excellent slope so that the water drains away.

Advantages

  1. PROVIDES SLOPE
    The system provides an excellent slope for the water to drain away and since water does not accumulate there is no leakage. Also it has a certain water retaining capacity and water is absorbed by the brick when it rains and released when it stops. Of course overloading results in leakages

Disadvantages

  1. CRACKS DUE TO TEMPERATURE VARIATIONS
    The brick bat coba treatment through successful in the damp heat of coastal regions cracks up completely on contact with the variations of temperature faced in North India between day and night temperature.

  2. IMPOSES UNNECESSARY LOAD
    This system has the disadvantage of imposing an unnecessary load on the system. Once cracks appear they are almost impossible to repair and water as in the case of the tar felting travels below the coba and exits wherever it finds a path. It is impossible to trace the inlet point let alone repair it.

  3. ALMOST IMPOSSIBLE TO DISMANTLE FOR REPAIRS
    Some parts of the coba stick so well to the concrete that even if an attempt is made to dismantle the system the slab gets damaged.

Verdict

This finds mention in tenders where specifications have been delivered by Consultants from Mumbai mostly but is unsuitable for any other region except the coast or wherever there are not to many variations in temperature.

Coatings

  1. EPOXIES AND POLYURATHENES
    Various membranes like epoxy and polyurethane are also used for waterproofing. These membranes also have excellent water repellant properties but

    • are very difficult to apply and

    • need very high standards of surface preparation to apply.

    The membranes therefore face very high failure rates since they can peel off. and once they start peeling the whole membrane comes off. As it is all epoxies have very low adhesion unless the surfaces are well prepared.

  2. POLYMER CEMENTATIOUS COATINGS
    There are also cementatious coatings available that consist of mixing a polymer with cement and applying on the surface. This gives a flexible membrane but

    • On unstabilized surfaces are of no use. All product catalogues mention this by stating that the surface must be properly prepared without mentioning how. Obviously any surface where the product fails is as per the manufacturer a badly prepared surface.

    • Have very negligible crack bridging capacity. Whenever the substrate shows even minor cracking these also crack with it

  3. POLYETHELENE MEMBRANES
    Polyethylene membranes are also used at times but are difficult to apply and also very costly as compared to other integral waterproofing methods.

  4. PENETRATING COATINGS

    The coatings that are most effective and can also act against water pressure are the penetrating coatings that are mineral based and have been in the market for more than fifteen years now. These have a crystalline action and penetrate the capillaries and form insoluble hard crystal in them and make the concrete or cementatious surfaces water tight. These are again to be used only as part of a complete systems in integral waterproofing and not as stand alone systems.


    Integral waterproofing

    In the light of the above it is clear that all the existing systems have some defect or the other and that no one system can take care of all the waterproofing problems faced and multiplicity of the problems require individualized solution. These are provided by the latest trend in waterproofing by the use of the construction chemicals. Since the number and type of chemicals in many they have to be used in different combinations to get the desired results. Their use calls for the use of specialized knowledge but offers the advantage the solutions are tailor made for different categories of problems.

    Basic approach in Integral Water proofing

    The basic approach found to be useful in the application of construction chemicals is to cast as good a concrete as possible so that the concrete itself is watertight. It should be rendered watertight by making it denser and rectifying the various defects like honeycombs, capillaries, cracks etc. are corrected in the body of the concrete itself. This makes the concrete strong and dense and a stronger concrete is more likely to be watertight over a longer period of time than a weak concrete that is covered with some barrier.

    The systems in the following pages are designed keeping in view this basic approach whereby membranes are used at a minimum and when used are only supplements for the other systems. The techniques used are many and consist of injection grouting, polymer repairs, and addition of integral additives and even ferrocementing. Also more than one set of chemicals are used at a time so that the waterproofing is totally fail-safe.

    These are by and large the most modern of systems AND the rest of the section on waterproofing is devoted to details of how they are used.

    It should be born in mind though that the use of construction chemicals in an aid to good civil engineering practice and not a substitute to the same. That they are substitutes to good civil engineering is a myth though not propagate by construction chemical companies is yet not discouraged by them.



1 comment:

  1. interesting blog. It would be great if you can provide more details about it. Thanks you



    Waterproofing Chemicals

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