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Sunday, 19 February 2012

WATER PROOFING FOR ROOFS

 

  Terrace is the most crucial segment of a building, and it is exposed to direct climatic variations, extremes of rainfall and structural movements caused thereby. So every effort should be taken at the design stage itself to ensure that a proper protection system has been incorporated. It has often been found that the economic solution is not always the best solution. So, the system, which assures maximum protection, should be selected even though it may cost little more.

 

IMPORTANCE OF WATER PROOFING FOR ROOFS

A building or structure needs waterproofing as concrete itself will not be watertight on its own. All the flat roofs in the modern age are generally constructed of reinforced cement concrete. This material removes all the problems of flat roofs except that the roof should be made water proof by employing any of the various methods available for moisture proofing.

·         USUAL PRACTICE

The R.C.C. Slab of the terrace is generally done with ordinary concrete without using any admixture to take care of the extra workability required to proper placement and compaction of the concrete through the congested reinforcement.

Sometimes integral waterproofing compounds are used in the concrete. But often they are not used properly or sufficiently. Lime terracing, i.e., Brickbat coba with lime, is done on the R.C.C. slab to serve dual purpose. First is weatherproofing of the slab by providing heat insulation for the area below it. The second purpose is waterproofing. This layer also provides the slope required for easy drainage of rainwater. The parapet is of brick masonry and plastered with ordinary cement mortar.

·         PROBLEMS

1. In due course numerous cracks are developed in the lime terracing. Water penetrates through these cracks to the R.C.C. slab below it. Due to shrinkage of cement mortar, lots of cracks are formed on the plaster of the parapet walls. Rainwater seeps through these cracks into the bricks and slowly comes down to the R.C.C. slab.

2. Because of improper compaction, often the concrete of the R.C.C. slab is full of voids and honeycombs. Once the water reaches the R.C.C. slab, it easily seeps inside and corrodes the reinforcement, thus weakening the structure itself.

3. Water, after seeping through the R.C.C. slab, makes the ceiling and walls damp. In severe cases water starts dripping from the ceiling. All these leave ugly patches of dampness on the ceiling and walls and paints peel off.

4. To avoid leakage of water through terrace, often tar felting is done on the terrace. But due to weathering, the tar felt gets cracked within a couple of years and water penetrates through the cracks to come down to the ceiling.

·         SUGGESTIONS

To protect the terrace it should be made properly waterproof. There are numerous terrace waterproofing systems available in the market; the choice of products will depend upon the requirements of the client under given considerations.

A. The environment conditions (dirunal and seasonal temperature variations) a building is subject to expansion/contraction caused as the consequence.

 

B. If the entire structure is weak for the reason of poor quality of construction, sub-soil being weak, vibrations from surrounding pattern of land use too vigorous etc., then terraces are likely to be affected. A waterproofing system should allow such movements. However, if the movement is too significant and the structure is not designed to overcome the same, then none of the waterproofing systems will last unless adequate structural strengthening is done prior to waterproofing.

C. Insulation properly desired - some structures are designed to retard excessive heat penetration through the terraces to the areas underneath. At times lightweight concrete is used. In such cases a strong waterproofing layer becomes most essential, because the surface has an element of porosity.

D. Terrace garden - Continuous presence of water and contact of organic matter would require additional treatment of waterproofing than normal ones.

E. Cost factor - Quality and durability of a system is directly proportional to cost. If the budget available permits an option for a cheaper system only, then we could recommend such treatment.

·         TYPES OF SYSTEM

Terrace-waterproofing is possible with varying permutations and combinations within a wide product range, to suit the 'tailor-made' requirements of the clients.

1. Whilst any water proofing system is decided, it is imperative to have a basic substrate, which is structurally sound. If the base on which a waterproofing application is done, happens to be weak, then the system chosen will also weaken. In order to have the base concrete strong enough, the concrete should be admixed with an integral waterproofing compound which would give a homogeneous, workable mix at lower water/cement ratio and reduce the permeability. It should be ensured that the terrace is given a proper slope. Any standing water shall not be permitted. Many waterproofing systems have been found to fail because of standing water remaining on the surface consistently for longer duration.

2. The concrete, after casting, should be cured by ponding or sprinkling water or with a suitable curing compound spread over the entire surface. Initial curing is critical and should start immediately after the initial setting of the concrete, say after 4 to 6 hours of placing concrete. Lack of initial curing is the main cause of drying shrinkage cracks.

3. For construction of the parapet wall, a suitable mortar plasticizer should be used with the bricklaying and plastering mortar to improve the quality of the mortar.

4. Before starting any treatment for waterproofing of the slab, all the visible cracks, undulations, joints etc. should be taken care of with a suitable waterproof repair mortar.

5. On the cured and repaired concrete surface, there are 3 alternatives, which can be considered for waterproofing.

Alternate 1

After taking care of all the vertical and horizontal joints with the waterproofing mortar, the concrete surface may be treated with a surface applied cement based, crystalline action, hygroscopic waterproofing chemical and then covered with layer of cement mortar (25 to 75 mm) admixed with a mortar plasticizer (commonly known as IRS finish.) Expansion joints and Dynamic cracks shall be filled with flexible and waterproof sealing compound.

Alternate 2

After taking care of all the horizontal and vertical joints with the waterproofing mortar, the concrete surface may be treated with a polymer based, flexible waterproofing chemical, which would take care of thermal movements. Then the terrace may be finished as in alternative 1.

Alternate 3

Where the terrace is likely to come in contact with water and organic matters regularly, as in roof gardens the terrace should be treated with epoxy resin based surface waterproofer.

6. The plaster of the parapet wall should be treated with a resin based water repellant chemical to avoid any chance of water seeping through the wall down ward to the concrete slab just below the wall.

7. If the brickbat coba or surki is to be done on the terrace for weatherproofing, that should be done only after the waterproofing treatment is done. An admixture should be used with the surki mix to make it watertight itself.

 

METHODS FOR WATER PROOFING

Water proofing can be done by the various following methods:

1.      Brick Bat Lime Coba Treatment

2.      Mud Phuska Treatment

3.      Bitumen Coating With Sand Sprinkling

4.      Bitumen Felt Treatment and Glass Fibre Felt Treatment

5.      China Mosaic Treatment

6.      Indian Waterproofing Method

7.      Oversees Waterproofing Method

8.      Proof Solution Method (by Nina Industry)

9.      Leak Proof (by Water Proofing Corp, India)

10.  Aqua Proof (by ACC)

11.  Roof-Con (by De-Rust Chemical Corp)

12.  Aqua (by Crystal Chemical)

13.  Britex 100 (by Britex Chemical Industries)

14.  Poly Urethane Foam (by Oversees Water Proofing Company)

15.  Latex Phalte W H (by Synthetic Asphalt)

16.  Silicon Based Water Repellant (Syltrit 1772)

17.  Epoxy Coal Tar (Paribond)

18.  Aqua Seal

19.  Mendo

20.  Chime Seal

21.  Epoxy Painting Or Grouting

22.  Cico, Puddlo, Impermo

23.  Snowcem

24.  M-Seal & Epoxy In Various Formulation

25.  Polythene Trt

26.  Mastic Asphalt

 

These are some of the methods that are employed for water proofing of roofs. There are many more techniques available which can also be used in combination with these methods.

 

 

 

PRINCIPLES OF WATER PROOFING FLAT ROOFS

The functions of any dwelling unit are broadly three in number:

1.      Protection from rain

2.      Shelter from extreme cold or heat

3.      Privacy and safe storage of possessions

The evolutions of modern dwelling units- call them flats, houses or bungalows- can be traced to natural caves, which must have been the earliest form of shelter. Traditional house types have developed in response to the needs- when agriculture was the predominant occupation or business, over a hundred years or so, the building materials were provided by the neighboring country. Everybody was a house-builder as he was a herdsman or an agriculturist. Today we are living in a world of specialists and specialization. We have masons who can do wonders in stone but not brick and vice-versa. In the same way we are looking at a particular aspect of construction technology and methods and maintenance; that of water proofing and that too terraces.

Architecturally, terraces would imply a flat-roof or an open platform. The other meaning is a colonnaded porch or a promenade or a porch. In the mountainous region in our country, especially in north and north-east, where flat land is minimal, hill slopes are flattened at different levels and look like steps. An ingenious system of channel provides water to each flat piece of land and rice is grown. This is known as terrace cultivation.

Today our terraces in construction provide a very useful space, practically for anything, drying, storage, parties, and functions and so on. The terrace performs the same functions as the courtyard, which once formed an integral part of the vernacular architecture of Indian houses.

On one hand, we need terraces functionally, while on the other we perceive it as a problem area, as it often is the source of unwanted water, in form of damp, or water seepage or as rain sometimes, even as rain has stopped outside.

Not so long ago, flat roofs or terraces were a byword for trouble and there was a common saying was that the only way in which the problems of a flat roof could be avoided was only through building a pitched roof over it. But in the recent years, there have been advancement in materials and design choices and the record of terraces has improved tremendously.

Historically also, terraces did have problem of leakage and some solutions must be found. Perhaps the degradation of material does cause permeability or cracks or both, volume changes, shrinkages, expansion, entrapment of water- all these caused by the characteristics f the materials cause us problems. Many new materials provide us with novel solutions also.

Many concrete structures are designed and built to:

·         Contain water within the structure

·         Maintain dry condition within the structure, where it is subject to water conditions on the outside

We are looking at the second condition, wherein the roof or the building envelope at the top of the building has to keep the water away. The water is due to rain and in the part of the world where we live in, it is the monsoon rain, severe at times, more than 25 -30 mm of rain per hour and over 250 cms in most parts of the west coast. We are also looking concrete, which is used as the structural slab with beams and columns of the structure.

Since concrete is not completely impermeable to water and since concrete may sometimes develop cracks after placement, it is sometime necessary to cover the surface with a barrier material to meet these requirements.

To understand the factors affecting the performance of various barrier systems, it is necessary to consider them not isolated, but as a part of the whole.

The specific elements are the barrier materials, the interface of the barrier and concrete surface, concrete to a depth of 6 -10 mm, the reminder concrete and supporting systems.

Awareness of the systems concepts will make one appreciate the selection of barrier material is only one of the many inter related steps to offer satisfactory performance. Equally important are placement, consolidation, curing of the concrete, surface cleanliness, surface preparation, application procedure and inspection.

A decision to use a barrier and its selection should be made when the concrete structure is being designed. Configuration of the structure, construction methods and job sequencing can affect barrier installation and quality. Barrier penetration can be minimized and barrier aspect of the job better planned.

Concrete is a material par excellence. One only needs to appreciate its behavior in the environment, in which it is to function. We live in a tropical climate- parts of the country are hot and arid, whereas along the western coast we are in hot and humid climates with heavy precipitation. The environment clearly has two different phases. In the hot part of the year it is subject to nearly 40.C ambient temperature and unless insulated it could reach up to 70.C and the interior of the dwelling unit can be uncomfortable to live in.

Thus it appears for the roof we really require two barriers- against heat and against water. The traditional approach has been to provide a lime terracing (100 to 200 mm thick) comprising of lime, surkhi and brick bats along with many indigenous admixtures- both organic and inorganic. Such a layer functioned to provide both courses of weathering course- the insulation part and the water proofing part; the top level of the course being so adjusted to have the water flow freely into the drain outlets.

Today flat roofs are much more than just that. At their periphery usually there is a parapet wall provided about a meter high. The dwarf wall with 1:3 (or leaner) cement mortars and at times a stone coping is provided. If we look at the roof, wall in it’s entirely; we see a water tank, by and large. Of course the rain water outlets are there. Imagine these outlets, which have some grills, blocked by leaves and other debris, when it rains we do have standing water. Even when the other outlets are not blocked, when there is a very heavy downpour, many of us many of us may have seen a pool of water increasing or decreasing. When such is the case, that is we have a water tank literally, should we not go for the same specifications as we do for an RC water tank or reservoir, lower allowable stresses, crack free, neat cement punning and all proper joints and all of the rest of it. Otherwise if it does not behave like a water tank, are we not to blame ourselves.

Concrete leaks due to the following reasons:

1.      Thermal Variation

2.      Long Term Drying Shrinkage

3.      Crack In Transition Zone

4.      Structural Stresses

5.      Creep Deformation

6.      Thermal Incompatibility Between Paste & Aggregate

7.      Rusting Of Steel

8.      Sulphate Action , Moisture Movement Due To Volume Change

 

In many countries, the roof is variably sloping roof- sometimes steep and sometimes not so steep. This has been our tradition. But in the recent years, for various reasons, we have dragged a flat roof from a relatively arid, low rainfall area where it works very well, to the west coast also. This is perhaps a folly. It would still be useful is possible to provide a sloping roof, with purlins, rafters and tiles taking off from a short parapet wall, or limit the terrace part to only the periphery of the building. This is what is done for many buildings even today in Malaysia, where the climate is like ours.

Of course- timber is scarce- we can have alternative material like steel and aluminum. Actually the RC roof will then function - more like false ceiling perhaps we will design it with lesser dead loads- access not provided and no lime terracing or brick bat coba.

Of course if this is done all over, the water proofing contractors will curse the architects and engineers for the change.

The general principles for a successful weathering course consist in knowing about the correct procedures for their installations together with incorporating sufficient details in the planning of the job.

Rain water must be drained effectively and quickly off the roof and it should not be allowed to pond. To achieve effective drainage a minimum fall of 1 in 80 is recommended. Allowing for construction inaccuracies and roof deflections, it is advisable to design for a fall of 1 in 40, correct detailing is necessary to see that rain water discharges into the drain pipes properly.

Modern materials are all excellent. However they could be quite sensitive to variance in application if not done properly, as per instructions. The manufacturer’s guidance when in doubt is essential.

 

ANATOMY OF WATER PROOFING

Significant factors contributing towards the dampness coming from the terraces into the soffit of the ceilings are:

·         The entry of water through cracks in external plaster

·         Failure of pointing

·         Hollow left due to insufficient grouting of stone masonry

·         Capillary action

·         Incorporation of incompatible components like RCC lintel bands in stone/brick masonry walls

·         Flashing of water on external surfaces

·         Inadequate and imperfect expansion structural deformations etc.

 

NEED OF WATER PROOFING PRODUCTS

Ideally concrete, the most widely and regularly used construction material is supposed to be water tight with co efficient of hydraulic permeability between 10-8 to 10-10 m/sec. a well made concrete with proper mix design and with proper pouring and curing practices is regarded as a very low porous material. However it is seen in practice that concrete loses its permeability due to the following reasons:

1.      Improper gradation of materials

2.      Excessive water cement ratio

3.      Less compaction

4.      Awkward architectural section

5.      Improper shuttering

6.      Cold joints shuttering either in mass concreting or in tall vertical structures

7.      Use of bad quality construction materials such as corrosive reinforcement or reactive aggregates

8.      Lack of curing : timely curing specially in high cement content concrete mix or where high grade cement is used in plastering

9.      Damage to structures due to earthquake effects

10.  Failure of plumbing

 

 

 

TYPES OF WATER PROOFING METHODS

Water proofing can be broadly classified into the following types:

·         Traditional Waterproofing Methods

·         Modern Waterproofing Methods

Some of the Traditional Water Proofing Methods are

1.      Integral Waterproofing Compounds

2.      Brick Bat Lime Coba Treatment

3.      Mud Phuska

4.      China Mosaic

5.      Indian Waterproofing Method

6.      Shalimar Treatment (Tar Felt)

·         Hessian Felt

·         Glass Fiber Felt

·         In-Situ Glass Fiber Felt

7.      Bitumen Coating With Sand Sprinkling

8.      Poly Ethylene Film

9.      Aluminum Foil

Some of the Modern Water Proofing Methods are

1.      Silicon Based Water Repellent

2.      Polymerized Bitumen

3.      Water Proofing By Crystallization (Cement And Liquid Polymer)

4.      Water Proofing Membrane Forming Coating

5.      Polymer Based Water Proofing Compound Ready To Use

6.      Water Proofing Tile Adhesive

7.      Protective And Decorative Coating

8.      Injection Grouting For Cracks

9.      Poly-Sulphide Joint Filler

10.  Silicon Sealant

 

 

A number of new products with different combination have come to the market in the recent past, to overcome the disadvantages of normal bitumen based products. Salient features and recommended areas of applications are given below:

 

MODERN METHODS OF WATER PROOFING

 

 

 

STAGES OF WATER PROOFING

Water proofing as a process needs to be take care of at two stages:

·         During Construction Stage

·         Post Construction Stage

 

STAGES OF WATER PROOFING

This diagram only gives a basic idea regarding the number of water proofing methods available. Both the stages- construction stage and post construction stage- are equally important for effective water proofing.

A.     DURING CONSTRUCTION STAGE

Some of the essential precautions to be taken at the time of construction are as follows:-

1.      Every building plan, whether for new building OR for addition/alteration to new building, must give details of terracing to be provided , water proofing system for roof with details of joint with parapet wall, sunken floor and down water pipes in scale not smaller than 1:20.

 

2.      Specifications laid down by the manufacturers of the water proofing products should be followed scrupulously to ensure that no air bubbles are left between the under lying surface and the water proofing layer. Adequate overlaps should be provided for the water proofing layers, including cover up to the parapet wall. There are a large number of relevant Indian Standards and Code of practice available.

 

3.      Drainage slope of the roof is one of the most important factors. For the guidance of the field Staff, each building plan must also incorporate a roof plan, showing the position of drainage Pipes and direction and extent of slope on the roof. Drainage slope should not be flatter than 1 in 80 and should preferably be 1 in 40. There should be no undulations in the roof surface, which may result in accumulation of rain water. At the time of construction, the roof levels should be personally recorded by the Inspector of Works and 100% check exercised by the Assistant Engineer. Extra care is necessary for construction of golas, coping and joints.

 

4.      At the extension joints in buildings, water proofing has to be strengthened by inserting a PVC Or a copper plate to prevent water from seeping. These joints should also be plugged by a good sealant. Polysulphide based flexible sealants have good adhesion to concrete surfaces and can be compressed or stretched upto 50% of the width of the joints and are good material for sealing of expansion joints. Depth of the expansion joints above the copper/PVC plate should normally be kept half of the joint width and should not exceed 20 mm.

 

5.      Special precautions should be taken for sealing of area around the water spouts to make them water proof.

 

6.      Any type of impermeable layer/coating should never be applied on both faces of the wall as the wall must be allowed to “breathe”. A non-permeable finish or waterproof finish should not be applied on a wet wall, as it takes a long time to lose water used during construction. The interior of a new building should preferably be provided with lime based color wash.

 

7.      Quality of casting of concrete slab and quality of terracing has to be good and strictly as per specifications. Dense and low permeability of concrete also ensures relief-from dampness and comes by adequate cement content and low water cement ratio in concrete apart from required level of compaction and adequate curing.

 

8.      Area surrounding plinth of the building should be filled with good earth and rammed with slope away from the building, preferably with plinth protection apron.

 

9.      Proper drip course should invariably be provided on parapet wall copings, sun-shades, chajjas etc.

 

10.  Sunken floors are a constant source, of leakage and dampness. These floors are provided for accommodating the toilet seats. Sunken floors must invariably be coated with suitable epoxy or polyurethane compound or polymer cementitious waterproofing compound. These coatings should be given over the slabs as well as on the walls up to 40 cms above the floor level.

 

11.  Proper distribution, design and installation of joints in the building e.g. expansion/contraction and construction joints and maintenance thereof can go a long way towards improving the water proofing of the building, since any crack may give rise to ingress of water.

 

12.  Adequacy of drainage must be ensured. As a general guide line for every 40 M2 of roof area, one 100 mm diameter rain water pipe must be provided. Drainage will also depend upon the intensity of rain fall in the area. Softer/compressible finishing material for roof surface like lime concrete or mud phuska, which may develop local depressions, will need steeper slopes.

 

It becomes all the more important to take care of water proofing in the construction stage. Some of the methods have been described below:

1.      Concrete Admixtures

Many of the concrete plasticizer and super plasticizer complying to  IS 9103 act as water reducing agents, thus reduce permeability of concrete and also comply with IS 2645 requirements, at reduced water cement ratio.

2.      Integral Water Proofing

Available powders as well as liquid form, integral water proofing compounds are the most popular and commonly used products. Here, powder water proofing is to be mixed with neat cement, which subsequent by will be used for products. Here powder water profess is to be mixed with neat cement, which subsequent by will be used for preparing mortar or concrete liquid. Water proffer is to be mixed with dosing water, which can be used in cement mix or dry concrete mix.

Such compound will be effective only when water cement ratio is controlled and proper inter locking of ingredients of concrete is observed to get a cohesive mix based on particular size distribution, while designing concrete mix.

Depending on nature of crack, suitable product is suggested. Hydraulically fast setting non-shrink powder is used after widening.

Hairline cracks and making ‘V’ grooves using cutter machine. Water is added for obtaining trowel able consistency and crack is filled with gloved palm or steel spatula. There are products also used for plugging running leakage from water tank, RCC Hume pipe and can be used under water in fully submerged conditions.

Semi-liquid acrylic flexible sealer can be used where thermal stresses are high and crack tends to expand and contract. Such products are user friendly and can be used by anybody without any hitch, without any special tool tackles/training.

3.      Expansion Joint Treatment

Poly sulphide silicone or polyurethane silicones are used depending upon specifications and user preference. Polysulphide is grey in color while silicone sealant is colorless or white in color. PU can be made available in few selective colors. Most important here is movement accommodation factor.

Size of expansion joint and distance of joint is design aspect and is in preview of consulting engineers. However, correct joint preparations at edges and bottom surface and application methodology here is of utmost importance. Epoxy mortar is used to repair worn out broken edges and expanded polystyrene /PUF / bituminous board are used as backing materials for such joints.

4.      Water Proofing Coating

Depending on basic materials, water proofing coatings can be divided into the following types:

a)      Silicate based crystalline penetrating type single component powder

b)      Single or two component polymer modified brush applied coating

c)      Single component epoxy based liquid coatings

d)      Epoxy or polyurethane coatings

Due to its moisture sensitive nature, epoxy and PU coatings have not become very popular. Care should be taken to protect the coating against mechanical damage using screed or plaster on top of it. Coating can fail if proper surface preparation is not observed. Manufacturer’s recommendation must be followed religiously.

5.      Exterior Water Repellent Coating

Silicone/ silane/ siloxane based color less coating is applied on exterior face of buildings for:

a)      Protection against salt efforance formation

b)      Protection against growth of algae or fungus

c)      Prevention of water seepage through hairline crack in external plaster

d)      Protection of exterior paint for longer duration

Silicones water repellents are of two types:

·         Water based- having lesser life span

·         Solvent based- having life of 5-10 years. Silicone water peller is very cost effective. Solutions which can be applied on various substrate such as bricks, stones, cement, paint, stone cladding and many more.

 

6.      Water Proof Concrete Film

Aquascud is a patented “sandwich” made of two waterproof concrete films with interposed inside an elasticized membrane which is micro-porous and hydro-repellent (the “shield”). A total thickness of 3 mm that forms up a really safe barrier impermeable to water (no permeability up to 1,5 atm)      FIGURE 3.1 – LAYERS OF WATER PROOF CONCRETE FILM

that adapts to the deformations of the structure thanks to the high elasticity of the system (crack bridging ability 1,5 mm).

 

B.      POST CONSTRUCTION STAGE

Water proofing needs to be done not only during the construction stage, but it also may happen that the existing buildings may experience dampness. The following table helps in analyzing the reason for dampness in existing buildings:

: WATER PROOFING IN CASE OF EXISTING STRUCTURES

In case of repair work for a leaking roof, the procedure is different from the water proofing done during construction stage. The method has been described below:

·         Remove the existing water proofing treatment, whether brick bat coba or bitumen felt to expose the sound RCC surface.

·         Repair any cracks or honey combs with prema crack fill to get an even workable surface

·         Mix the guard and apply with a brush and immediately cover it up with cement sand screed. Lay back the brickbat coba to provide water proofing is so desired.

Materials:

·         Water proofing seal slurry

·         Water proofing guard

·         Fiber mesh

·         Proof solution

·          Polymer (chemical)

 

 

 

 

 

 

 

 

 

 

 

 

                                                                WATER PROOFING OF EXISTING STRUCTURES

 

 

 

 

LIME COBA AND LIME CHEKA 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.  

 

1.      LIME COBA

            Lime Concrete is made as below:

·         Brick Bat (100 mm size) – 40 parts

·         Lime mortar 1:2made with sukhi – 50 parts

·         Admixtures – gud, bel fruits, resins, white of egg, methi and udad      cereals

 

3 kg of Gud Jaggery and 1.5 kg of bel fruit are added to 100 litres of water by boiling and this solution is sprinkled while tampering. In South India the solution of Terminalia Chebula (Kadukai) is prepared by breaking dry nut to small pieces and soaked in water. Proportions are 6oo grams of kadukai, 200 grams of jaggery and 40 litres of water for 10 m2 area. The solution is brewed for 12 to 24 hours. Resulting liquor is decanted and used in the work. Some people have used soap solution. The lime mortar is ground usually in bullock driven ghaani for 21 days. When it becomes suitably flexible, then admixtures are added and concrete, which can be consumed in one day. This concrete is spread over flat roof stone slab. About 112 mm thick layer is spread and finished with appropriate slopes 1/60. The sides of parapet wall are also finished with a curve so that there is no leakage.

 

From the next day the lime concrete is tamped by wooden rammers and while tamping a liquid of Bel and Gud is sprinkled. The tamping continues for 10 days. Young girls of age 15 and below usually do the tamping so that it is a light and rhythmic tamping. They sing traditional folk songs during tamping. This imparts rhythm to the lime concrete mass. The top surface is finished with white part of egg and made smooth and glossy. Many other materials like methi and udad dal are added with lime to make it flexible and ductile. This technique was used for waterproofing of RCC roof at Medical College Jabalpur in 1971-72 where soap solution was used for sprinkling over coba.

2.      LIME CHEKA COBA

This is very popular in hot areas of Gwalior and Rajasthan when temperature rises upto 47 degree celcius. In this treatment, small water pots 75 mm high are kept over stone slab with top of opening facing the stone. Lime concrete is first filled in space between small 75 mm high pots and then 75 to 100 mm above and it is tamped for 21 days. The hollow pots impart thermal protection to the space below.

In place of hollow pots, thin 12 to 15 mm thick bricks of size 75x75 mm are placed in vertical profile in various patterns, rectangular, square or circular. Lime concrete is spread in the space between them. Then top 100 mm thick lime concrete layer is spread over it and finished in a similar process.

Both the treatment can last up to the life of the building and there may not be any need to replace them. In old buildings replacement is done after 200 years.

Cost of lime concrete cob a treatment will be about Rs. 500 per sq.m. Cost of water proofing treatment with polymerized material is Rs. 250 to 300 per sq.m. The traditional treatment is more time consuming and costly. But it can last for 100 years.

FIGURE 4.1 – BUILDING SECTION SHOWING THE VARIOUS LAYERS FOR LIME COBA

BITUMINOUS FELTS AND POLYMERIC BITUMINOUS SYSTEMS

It is a generally provided water proofing treatment for old roofs showing signs of leakage. Mixture used is as follows:-

COAT

BITUMIN

(Blown Grade of Bitumin)

Conforming to IS-702-1988

MINERAL OIL

APPLICATION MEANS

Prime Coat Brush

2

3

 

Under Coat Brush

3

2

 

Final Coat

Neat

 

Wooden Trowel

TABLE 4.1 – BITUMINOUS FELTS MIXTURE FOR EXISTING STRUCTURES

Primer coat is applied with brush over dry clean surface and allowed to dry for 24 hours. Second coat is applied next day and final coat is applied third day. It is finally covered with 2 cm thick coarse sand or gravel.

WATER PROFING WITH BITUMEN FELT

Hessian based tar felt is the most common product for water proofing on the new roofs. These felts use hessian as the barrier medium for bitumen and bituminous compound. Bitumen felts are classified as Type 1, 2, 3 depending on type of base used in their manufacture and the uses for which the felts are suited. Grades refer to minimum weight of bitumen felt -

The bitumen felt should be laid over finished roof surface of slope not flatter than 1 in 120.

In normal weather conditions the treatment should consist of 4 courses as under:-

- Hot applied bitumen @ 1.2-1.464 Kg/Sqm.

- Hessian base self- finished felt type 3 Grade I.

- Hot applied bitumen @ 0.7-1.2 Kg/Sqm.

- Pea size gravel or grit @ 0.006-0.008 Cum/Sqm.

 

For severe climatic conditions and important structures/courses heavy duty treatment should be given as detailed below:-

·         Hot applied bitumen @ 1.464 Kg/Sqm minimum.

·         Hessian base self-finished felt type 3 Grade I. 

·         Pea size gravel or grit @ 0.008 Cum/Sqm.

Two types of bitumen can be used and treated as detailed below:-

i) Bharat Industrial bitumen R-85/25 (I.S.702) – 177 C.

ii)Bharat bitumen 30/40 (I.S.73) – l77 to 191 C.

In the laying of 4 or 6 courses of bitumen felt, as the case may be, over the last course of hot bitumen, stone grit or gravel of 6 mm and down size shall be spread uniformly on horizontal surfaces.

Bitumen felts suffer from following deficiencies

a)   Contents of a factory finished felts are not viscous enough to retain the shape and intended characteristics of roofing felt. High viscosity is desirable as it ensures better life for waterproofing system and helps retain its flexibility over longer duration.

b)    Defective lap joints allow seepage of water.

c)    Hessian being organic in nature is subject to decay within a short time, resulting in decrease in tensile strength and life of tar felt.

Now glass fibre reinforced bitumen felts are also available in market and can be used in place of vegetable fibre or hessian felts.

 

 

 



WATER PROOFING FOR ROOFS WITH BITUMEN FELT

STANDARD APPLICATION METHODOLOGY: BITUMEN BASED SYSTEM

There are certain essential pre-requisites for any bitumen based water proofing system to be successful.

These are:

·         The surface to be treated should be smooth, having proper slope.

·         There should be no depression or cracks

·         The surface should be bone dry.

·         Any structural defaults in the roof or the parapet wall should be attended to before starting the treatment.

·         Detailed steps in laying of the bitumen based surface barrier systems will be:-

i) Make surface smooth, even and dry, remove local depressions and loose dirt.

ii) Paint the dried surface with bituminous primer and allow it to cure.

iii) Apply foundation coat of bitumen.

iv) Lay surface barrier membrane i.e. bitumen felt.

v)  Apply on coat of bitumen and finish with grit or coarse sand.

 

 

 


 

INTRODUCTION TO TERRACE GARDEN WATER PROOFING

 

Terrace gardening is a type of indoor gardening where you take care of your indoor plants.
Important features before gardening

·         The roof on which the gardening is to be done should be strong enough to carry the weight of the garden

·         The terrace should be sloppy with an effective drainage system.

·         Lastly there should not be any leakage of water in your roof garden.

STRUCTURING TERRACE GARDEN

1.      Unlike any type of gardening this terrace garden also needs a detailed plan. It should be proportionate with lawns, shrubs, ground covers and small trees. If desired you can also assimilate the concept of water garden or rock garden or create a shady structure on your roof garden.

2.      The next step is the choosing of plants. Fiber-rooted plants are preferred to tap root system. Tap-rooted plants have the tendency to grow through the building causing harm to it.

3.      The soil that should be used must not exert pressure on the building. The adequate soil for this purpose is soil rite or peat moss. As it is a costly material you can blend it with garden earth, manure.

4.      To prepare your drainage system you need to do the roof garden construction. Lay only burnt bricks approx. 2" - 4" uniformly on the terrace. Burnt bricks are the best because normal ones turn into mud and collapse the drainage system. Corrugated sheets are another option and should be placed at 3' distance to make the water flow to the drain.

5.      In top of the bricks lay a net lawn. This will prevent the soil (prepared by you) to get inside the bricks.

6.      You have to construct drain at several places of the roof if it is quite large (say more than 500sq. ft.). Place pipes at several places leading to main holes. But be careful while laying pipes it should not be visible and gets covered by lawn when complete.

7.      Put the mixture of the soil prepared beforehand to the pot according to a level you choose. Then sow the selected indoor plants.

WATERPROOFING IN TERRACE GARDEN

The first and most important procedure is the waterproofing of the selected area. Buildings not older than 30 years that are RCC (Reinforced Cement Concrete) structures can be considered for a terrace garden. To begin with, the slab porosity is checked (for leakage) and accordingly steps are taken for waterproofing. At weak points, pressure grouting is done i.e. holes are drilled into the RCC slabs and via nozzles cement neat slurry is forced into them. Foam is formed and this fills all the holes, making the concentration of the slab denser.

The 90-degree angle formed where the floor meets the parapet wall is the weakest point and waterproofing is a must at these points. A cement-polymer mixture is used to reinforce these junctions. This procedure is called coving. Water-proofing plaster is applied at pipe junctions, sealing all the gaps where the pipe and the roof meet. Slopes are prepared if it is a new building; otherwise, existing slopes are examined to see if adequate drainage is present for excess water.

METHODS OF WATERPROOFING IN TERRACE GARDEN

·         Brickbat Coba

·         Integral Crystalline Waterproofing System

·         Atatic Poly Propylene Membrane

 

 

1.      BRICKBAT COBA

This involves laying of 80-l00 mm thick coba concrete on a prepared surface with graded broken brick aggregate. Concrete can be lime concrete or cement concrete with water proofing compound. This is useful for giving the surface the required slope so as to drain out water quickly. Since brick-ballast is hygroscopic, very good workmanship, mixing of all the ingredients in correct proportion and adequate compaction by rammers for lime concrete and by vibrators for C.C. is of paramount importance.

The brick bed coba is topped with IPS or with China Mosaic.

China mosaic is usually provided over a Coba surface by broken pieces of ceramic, China or Mosaic tiles are set over bed of cement mortar (1:3, 15mm thick).

2.      INTEGRAL CRYSTALLINE WATERPROOFING SYSTEM

An innovative technology is changing the way concrete structures around the world are waterproofed and repaired. Used for more than 30 years worldwide, “Integral Crystalline Waterproofing (ICW)” utilizes a chemical reaction to turn concrete into a permanent, waterproof barrier.

While conventional waterproofing involves applying a coating or membrane to the concrete surface, crystalline technology permanently seals concrete by plugging its natural pores and capillaries and blocking the movement of water. It also reacts with incoming water to self-seal the cracks that

inevitably develop in concrete, protecting structures against water and contaminants that can weaken or destroy concrete and corrode steel reinforcement. 

·         Working of Integral Crystalline Waterproofing

When added or applied to concrete, crystalline chemicals create a reaction that causes long, narrow crystals to form, filling the pores, capillaries and hairline cracks of the concrete mass. As long as moisture remains present, crystals continue to grow throughout the concrete, reaching lengths of many inches over time. Once the concrete has cured, the crystalline chemicals sit dormant until another dose of water (such as through a new crack) causes the chemical reaction to begin again.

The ability to reactivate in the presence of water gives crystalline-treated concrete the ability to “self-seal”. When cracks form due to curing shrinkage, settling, seismic activity, etc., water entering through them causes new crystals to form and grow, blocking and filling the cracks. Its ability to self-seal cracks is one of crystalline technology’s most unique and useful features, and can help to dramatically reduce the long-term maintenance and repair costs of a concrete structure.

·         Other Benefits of Integral Crystalline Technology

Along with superior waterproofing and self-sealing properties, integral crystalline waterproofing technology offers a number of key benefits:

Permanent solution – becomes a part of the concrete matrix so it will not crack, peel, tear or wear-away. Even against high hydrostatic pressure. Unlike externally applied membranes, which are best on the day they are applied, crystalline applications become more effective with time.

Perfect for blind-wall applications – can be added to the concrete mix or applied to the negative side of the structure (against the water pressure). There's no need to save room outside the structure for membrane application. Project teams can design a larger structural footprint and build right to the property line.

Protect reinforcing steel – adds to the longevity of concrete structures by preventing the penetration of waterborne contaminants and chloride-laden liquids that cause the corrosion of reinforcing steel.

Save weeks on construction schedules – can be applied to green concrete, or added to the ready-mix truck. There is no need to wait for membrane application and backfilling can begin right-away.

In hot or tropical climates, integral crystalline waterproofing offers several key advantages. Hot weather can dramatically shorten concrete’s setting time, resulting in weaker concrete and enhancing the likelihood of shrinkage and cracking. Adding crystalline chemicals to the concrete mix reduces premature moisture loss, creating a more durable structure and reducing shrinkage and cracking.  Unlike membrane systems that become brittle and deteriorate when exposed to prolonged heat, crystalline waterproofing is unaffected by climate and remains effective for the life of the structure. The soil in many hot or tropical climates can contain high levels of sulphates, chlorides and other chemicals that decrease concrete’s integrity and corrode steel reinforcement. By blocking the penetration of water that can carry these contaminants and safeguarding concrete and reinforcements against corrosion, crystalline technology helps to prolong a structure’s useful life.

·         Application of Integral Crystalline Waterproofing

In the case of new concrete construction, crystalline chemicals are supplied as a dry powder comprised of Portland cement, silica sand and special chemicals. This powder can simply be added to the concrete mixture at the plant to create a powerful moisture barrier in slabs, walls and construction joints. There is no need for any sort of surface application at the construction site.

Use of Integral Crystalline Waterproofing in Existing Concrete Structures

A number of manufacturers produce surface-applied formulas that can be brushed onto existing concrete structures to repair existing cracks, fortify and waterproof concrete and protect against contamination and steel reinforcement corrosion. The best systems may be applied on the negative side of the                 Figure 5.1 COATING OF CONCRETE

concrete against the water pressure where access to outside walls may be difficult or impossible. This allows concrete to be repaired without digging up the perimeter, destroying landscaping and incurring extra cost.   

When applied to existing concrete, crystalline chemicals are absorbed into the concrete by capillary action (the natural wicking movement of liquids through a porous structure) and diffusion (the natural movement of chemical molecules.)  Once inside the concrete, crystalline chemicals begin growing crystals and filling the spaces between concrete particles. The majority of active crystalline chemicals migrate into the concrete within the first 28 days, meaning the surface-applied system can be completely removed from the surface after this time without impacting its waterproofing properties.