Conventional Methods of Water ProofingWater Proofing is a process that is designed to prevent ingress of water into a structure. Water proofing, typically is executed in stages creating multiple barriers in the water path. Many a times, combination of different systems is adopted to suit the site condition for evolving an effective water proofing methodology.

In this section we describe conventional methods some of which are still in practice and some are completely outdated. Though methods like Mud Phuska, Brick Bat Coba, Lime surki, arecompletely outdated due to their limitations, they are still adopted in rural areas and by some consultants. It is also true that some of these methods are dealt at length in Indian Standard Codes as standard practices even today. Some of these systems have also improved in terms of application methodology, purification technique and have adopted modern tools for better workmanship.

Conventional Systems

Mud Phuska ( Outdated) Brick Bat Coba Method (Outdated but still being recommended by some) Lime Surki Method ( Outdated) Bituminous Method

o Hot Bitumen Paint system ( Outdated)o Tar Felt or Bitumen Felt system ( Outdated)o Built up Bitumen Membrane system ( In use)

Box Type Water Proofing ((Outdated but still being recommended by some) Lime Surki Method ( Outdated)

Mud Phuska System for Roof Slabs

This method of water proofing is most suitable for hot climates where annual rain fall is not high. This system also acts as a good thermal insulation layer for maintaining comfortable temperature inside the dwelling. The durability of this system depends on the maintenance of brick layer and slope for draining water from the surface.

Mud Phuska Terracing with Tile Brick Paving

Application Areas: Flat Roofs, Roofs with moderate slope

Mud Phuska - For Mud Phuska, selected soil which should be good quality brick earth not containing excessive clay or sand, free from stones, kankar, grass roots and such foreign matter, shall be collected and stacked at site. The soil shall not be collected from a locality infested with white ants. Before laying on the roof, the soil shall be made damp by adding water about 12 hours earlier.

It shall be turned over with shovels so as to break clods and to pulverize the same. Quantity of water to be added to the soil shall be carefully regulated so that the soil shall have optimum moisture content at the time of laying and compaction on the roof. The soil shall be laid on the roof to requisite thickness and slope, well compacted with wooden rammers, to obtain an even surface to correct slope. Average thickness of soil after compaction shall be as specified for the item.

A practical way of determining the moisture content of soil suitable for giving good compaction is that the soil should contain that much quantity of moisture, which, when a handful of soil is moulded with hand to the shape of a ball, it shall just retain its form. If the soil on moulding cannot retain its shape of a ball, moisture content is inadequate. On the other hand, if the ball can be plastically deformed on pressing with hand, the moisture content is on the high side.

Mud Plaster- After laying the Mud Phuska, the surface shall be given a coat of mud plaster 25mm thick and the plaster shall be allowed to dry and crack. The mud plaster shall be prepared from the same soil as for mud Phuska. The dry soil shall be reduced fine powder and mixed with water in a pit, adding fibrous reinforcing materials such as chopped straw in proportion of 35 kg per m3of soil. The choppings used shall not be longer than 2 cm.

The mixture shall be allowed to mature for a period of not less than 7 days. During this period, it shall be worked over at intervals spades and shovels so as to get a homogeneous mass free from lumps and clods. The mud mortar shall be puddled again very thoroughly just before use.

After the mud plaster has dried, the surface should be given a coat of gobri leaping so as to completely fill any cracks that may have formed in the mud plaster. Mortar for gobri leaping shall be prepared by mixing equal quantities of fresh gobar and finely sieved clay and adding sufficient water to form a thin paste. The quantity of gobar used in gobri leaping shall not be less than 0.03 cum per 100 sqm of plaster area.

Laying of Tile Bricks- After the gobri leaping has dried, flat tile bricks shall be laid using the minimum amount of plain mud mortar as bedding so as to obtain correct slope and even surface of tile floor. Care shall be exercised to see that mud mortar does not rise into the vertical joints of the tiles more than 12mm. The tiles shall be laid close to each other; the thickness of joints shall not be less than 6mm and more than 12mm in width.

After the tiles are well set and bedding mortar has dried, joints of the tiles shall be grouted with cement mortar mix of 1: 3 such that all the joints of the tiles are completely filled with mortar. Cement shall be mixed with 5% of crude oil by weight of cement and the surface of the finished roof shall be kept wet for a period of at least 7 days.

Curing - As soon as cement pointing obtains initial set, the surface of the tile brick floor shall be covered with wet gunny bags, hessian cloth or wet sand to prevent quick drying. After 8 - 12 hours, the tile brick floor shall be cured by frequent sprinkling of water on the surface for a period of 7 days. After curing has been done the surface shall be swept clean.

Slopes- The tile surface as completed shall be even and true to slopes of 1 in 48 or as specified and should be leak proof.

Brick Bat Coba Method (BBC)

Application Areas: Flat Roofs, Roofs with moderate slope, Balconies

Roof slabs need insulation for thermal comfort and waterproofing treatment to prevent leakage of water. Both these requirements are effectively full filled by BBC treatment.

Brick Bat Coba Method

Surface Preparation

All existing treatment, coatings on roof slab top is to be removed and surface cleaned by hard wire brush and washed with water. The surface should be free from any oil, grease, dust etc. Remedial measured by provided to all structural cracks. Expansions joints should be treated as per standard practice.

All non-structural cracks more than 0.5 mm wide and construction joints if any, should be cut in "V" shape, cleaned with wire brush and washed and filled with suitable crack filler. Cement slurry mixed with recommended water proofing compound is spread uniformly.

Application

Over this 15 mm thick cement, sand mortar, 1:4 admixed, with water proofer is laid. On the above green mortar, a layer of brick bats, soaked overnight in water, is laid, having an average thickness of about 110 mm, about 70 mm near rain water pipe and 150 mm at ridge and slopes as required are provided.

The gaps between the brick bats are generally kept between 15 and 20 mm. These gaps are filled with cement sand mortar, 1:4, admixed with water proofing compound either in liquid or powder form. It is preferable to mix the water proofing compound with the water prior to mixing it with mortar mix. In hot and dry weather, the surface should be covered with wet gunny bags immediately after finishing. Curing should start next day and continued for 7 days. The top surface is then finished smooth with 20 mm thick cement sand mortar, 1:4, admixed with water proofer. The surface when green is marked with 300 mm false squares. Curing is to be done by ponding.

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.

This system has some inherent disadvantages as below;

Cracks Due To Temperature Variations - The BBC 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.

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.

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.

Lime Surki or Lime Concrete Method ( IS 3036-1992)

Application Areas: Flat Roofs, Roofs with moderate slope

This method of water proofing is more suitable for hot and humid regions of India. This system requires high quality workmanship. The procedure for surface preparation is same as mentioned in earlier methods. 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-storeyed 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.

Materials

Lime- As far as possible class C lime (fat lime) in the form of hydrated lime conforming to IS 712: 1984 shall be used. Quick lime shall be slaked in accordance with IS 1635: 1975.

Coarse Aggregate-Coarse aggregate for use in lime concrete having maximum size of 25 mm shall be broken brick (burnt clay) aggregates conforming to IS 3068: 1986 or natural stone aggregates conforming to IS 383: 1970 depending upon the situation of use.

Water

Water used for both mixing and curing concrete shall be clean and free from injurious amounts of deleterious materials. Sea water shall not be used. Potable water is generally considered satisfactory for mix.

Preparation

Mortar for Concrete

One part of slaked lime and two parts of burnt brick pozzolana (or lime pozzolana mixture) by volume shall be mixed on a water tight platform. This shall then be sprinkled with the required quantity of water and shall be well ground in a mill or using mechanical grinder. Hand pounding may be done for small quantity. If hydrated lime is used adjustments shall be made in the proportion in accordance with IS 2250: 1981.

Coarse Aggregate

If coarse aggregate contains excessive dirt it shall be washed and well drained before use. Burnt clay or other porous coarse aggregate shall be thoroughly soaked in water for a period not less than six hours before use in concrete mix.

Mixing

Lime concrete may be hand mixed or small hand operated mixer may be used. For Iarge quantities the use of mechanical mixer would be desirable. Two and a half parts by volume of clean saturated surface dry coarse aggregate shall first be fed into the mixer and then one part by volume of lime. Pozzolana mortar as per 6.1 shall then be added to the mixer and the content mixed well.

Mixing shall be continued until there is a uniform distribution of the material. Final adjustment of water, to obtain concrete of required consistency may be made by adding clean water, if necessary, and turning the ingredients in the mixer.

Laying

Laying of lime concrete shall be started from a corner of the roof and proceed diagonally towards centre and other sides considering the slopes required for draining the rain-water smoothly. The average thickness of lime concrete shall not be less than 100 mm. In case the thickness is more than 100 mm each layer shall not be more than 100 to 125 mm.

If the roof is fat, slope not less than 1 in 60 shall be given. However, in case of heavy rainfall area slope of 1 in 40 is recommended. The minimum compacted thickness of the concrete layer shah, however, be nowhere less than 50 mm.

After the lime concrete is laid, it shall be initially rammed with a rammer weighing not more than 2 kg and the finish brought to the required evenness and slope. Alternately bamboo strips may be used for the initial ramming. Further consolidation shall be done using wooden THAPIES with rounded edges. The workmen will sit close together, and beat the surface lightly and in rhythm and move forward gradually. The beating will normally have to be carried on for at least seven days until the THAPI makes no impression on the surface and rebounds readily from it when struck.

If the surface during the process of compaction becomes too uneven that water lodges in pools, the surface shall be pricked and fresh lime concrete spread and consolidated as is necessary so as to ensure proper slopes and levels are being maintained with adequate bonding between old and new concrete by sprinkling requisite quantity of lime water. Special care shall be taken to properly consolidate the concrete at its junction with the parapet wall.

During compaction by hand-beating the surface shall be sprinkled liberally with lime water ( 1 Part of putty and 3 to 4 parts of water ) and small proportion of sugar solution or a solution prepared by soaking in water the dry nuts of Terminalia chebula for obtaining improved waterproofing of the concrete. On completion of beating, the mortar that comes on the top shall be smoothened with a trowel or float, if necessary, with the addition of sugar solution and lime putty.

Curing

The lime concrete after compaction shall be cured for a minimum of 10 days or until it hardens by covering with a thin layer of grass or straw which shall be kept wet continuously.

Finish

In case of accessible roof finish one layer of burnt clay flat terracing tiles may be laid over a thin layer of lime mortar. However, in the extreme condition where there is considerable expansion and contraction, two layers of tiles may be put on the top of lime pozzolana concrete. The tiles should be joined with non-shrinking impervious mortar by adding suitable integral waterproofing admixtures or 5 percent used engine oil by weight of cement and finished neat.

The protection against water penetration for the roof finish is enhanced by efficient drainage of surface water.

For this purpose, the slope of the terrace with lime concrete and tile finish shall not be less than 1 in 60 and the slope in the case of plain lime concrete finish shall not be less than 1 in 50. For every 40 m2 of roof area, one 100 mm diameter rain water pipe shall be provided.

Bituminous Methods (IS-1346-1991)

Introduction

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 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 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 de-laminate 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.

Following methods are discussed here.

Painting with Hot Bitumen Bitumen felt or Tar Felt Built up Bitumen Membrane

Painting with Hot Bitumen

The surface shall be painted when it is thoroughly dry. The surface to be painted shall be cleaned with wire brushes and cotton or gunny cloth. All loose materials and scales shall be removed and the surface shall be further cleaned with a piece of cloth lightly soaked in kerosene oil or bitumen primers.

Painting with Bitumen- The bitumen brought to site shall be in its original packing and shall be opened and used in the presence of the Engineer-in-Charge or his authorised representative. The containers shall not be removed from the site until the painting job is completed and the Engineer-in-Charge has a time to satisfy himself regarding the quantity of bitumen actually used and given his permission to remove the same.

The surface prepared and treated shall be painted uniformly with bitumen of approved quality such as residual type petroleum bitumen penetration 80/100, hot cut back bitumen or equivalent, after healing it to the required temperature as per specifications of the manufacturers. The coat of bitumen shall be continued at least 15 cm along the vertical surfaces joining the roof. In case of parapet walls, it shall be continued upto the Drip courses. Residual type petroleum bitumen of penetration 80/100 shall be heated to a temperature of not less than 180° C and not more than 190°C and shall be applied on the roof surface at not less than I80"C.

Similarly, hot cut back bitumen shall be heated to a temperature of not less than 165°C and not more than 170°C and shall be applied on the surface at not less than 165°C. Care shall be taken to see that no blank patches are left. The quantity of bitumen to be spread per 10 square metres of roof surface shall be 17 kg, unless otherwise stipulated in the description of the item and shall be carefully regulated so that the application is uniform at the stipulated rate of kg.

Spreading Sand- Immediately after painting, dry, clean sharp and coarse sand at the rate of dm3 per 10 sqm shall be evenly spread and levelled over the surface when the bitumen is still hot.

Tar Felt or Bitumen Felt Method (IS 1346- 1991)

Tar felt water proofing Very old system and not a permanent solution. 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 recommended 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.

Traditionally hessian based roofing felts impregnated with low grade bitumen are used as Bitumen Felts. These hessian fibers act as restraints in the flow of bitumen in hot weather, resist contraction during cold weather and essentially reinforce the membrane. During the manufacturing process, hessian fibers get saturated in the bitumen and subsequently as the matrices age, degradation sets in due to oxidation making the felts brittle. This characteristic of brittleness leads to ingress of water and the system fails.

Service life of Bitumen felts is about 5 years and effective water proofing not guaranteed. Due to this reason though Tar felting once universally used is found to be inadequate even for the primary function for which it is designed.

Disadvantage

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.

The specification clearly states that a light roller should be used on top of the tar felt 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.

A typical problem is that since the adherence to the surface is never complete channels get formed below the tar felting 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 tar felt

have to be carried out at points sometimes far away from the point that leaks and this is hard to identify.

Built up Bitumen Membranes

Application Areas: Flat Roofs, Roofs with moderate slope, Balconies, Open Terraces, Vertical Surfaces, Retaining walls, Basement water proofing

Built up Bitumen membranes are manufactured by immersing a roll of core material in bitumen and then coating it with oxidized or modified bitumen. In most cases the top side is also given a surface covering such as sand or slate granules and sometimes the underside is treated with an adhesive. The most traditional and lowest quality of the core materials to which bituminous coatings are applied is an absorbent fiber sheet.

Although this is cheap to produce, it is prone to tearing when being applied to roofs, and rots over time. Its poor quality makes it suitable only for low-level applications such as garden sheds, or as the bottom layer in a built-up roofing system where the

other layers contain higher-quality materials. But, because it is so cheap, it continues to be used as the sole covering on the roofs of some garages and domestic extensions.

The first higher-quality core material to appear was glass fiber sheeting, which was introduced in the 1950s. This is more resistant to tearing during application, and does not rot. It is suitable for a wider range of applications and, unlike rag-based felts, is used on commercial and industrial as well as domestic buildings.

The highest-quality core material is polyester which first began to appear in the 1970s. This is very resistant to tearing, does not rot and can be used for all types of flat roofs. The bitumen coatings for these materials are divided into three broad groups. The traditional one is oxidized bitumen which is the cheapest to produce, but lacks flexibility particularly at lower temperatures, has little capacity to cope with any movement in a roof and can become brittle and crack after exposure to sunlight. The other two coatings are achieved by mixing bitumen with a modifier which leads to felts which can be easier to apply, are harder wearing, and have a longer life and improved performance. Bitumen mixed with atactic polypropylene (APP) or the rubber-like styrenebutadiene-styrene (SBS) is particularly suitable for ‘torch on’ applications (see below) and is more flexible in low temperatures. Felts coated in SBS bitumen are more expensive than those which use APP, but are better able to accommodate movement in a roof without cracking.

There are two methods of providing and laying the bitumen membranes.

Pour and Roll Method

Laying of Bitumen Felt using hot Bitumen

This is the most traditional method and involves heating bitumen to a high temperature and pouring it on to the surface of a flat roof at the rate of 0.24 liters per square meter of surface area. The felts are then rolled on to the hot bitumen, forming a bond with the roof as the bitumen cools and solidifies. General application procedure is as under.

Clean the surface fully as briefed in the earlier sections. Clean the Bitumen rolls, remove the curls and cut to size taking into account the

corners, up-folds, down-folds, openings. Heat the bitumen to approximately 180 degrees and apply at the rate of 1.5 kg per

Sq.mtr. Roll the bitumen membrane and press using appropriate tools. Repeat the process with proper over lapping as per manufacturer’s recommendation. Ensure edges are anchored properly to the substrata to avoid lifts due to wind pressure.

Bitumen Felt Laying completed, ready for paint

Torch on Membrane Method

Torching of Membrane

In this method, the initial bitumen primer is avoided. The membrane before laying is heated using an LPG torch. As soon as the underside bitumen coat starts bleeding, the membrane is rolled and pressed flat. Rest of the procedure of overlap and precautions are same as in Pour and Roll Method. Minimum overlap recommended is 100 mm.

The membrane can either be partially or fully bonded to the substrate. The pour and roll and torch on technique will provide a full bond, this has the advantage of providing a high level of resistance to wind uplift and ensuring no flow path for water is provided under the membrane which could cause moisture to become trapped and blister the membrane.

However, a full bond will not accommodate thermal movement between the membrane and the substrate which could possibly cause the membrane to split or crack. Therefore, the first waterproofing layer is usually kept partially bonded and subsequent layers shall be fully bonded. Partial bonding will allow the waterproofing layer to be isolated from the substrate so that it accommodates differential movement that might otherwise cause it to split.

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. This method is quite popular with some designers and effective even now.

In this method stone slabs (Kota or 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 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.

Floor Installation

Preparation of surface by cleaning, leveling etc. 20 mm thick cement-sand-mortar mixed with water proofing powder, 4% by weight of

cement shall be laid on PCC and 20 mm graded aggregate free from impurities shall be spread on the floor. It shall be cured for 3 days.

Provide insert sockets and pipes to release the sub soil water pressure. Then 18-20 mm thick stones ( Kota or Shahbad) of approximate 600 x 600 mm in size

shall be laid flat and joined with cement-sand-mortar. This shall project 300 mm all around RCC raft. The stones shall be hard tough and free from cracks.

Then the surface shall be screeded with cement-sand mortar and finished smooth. RCC raft, walls or masonry shall be constructed as designed. The sockets / pipes are grouted with pressure. Columns or any support etc. coming out of raft shall be sealed with poly-sulphide

sealant at PCC level and at top of raft.

Wall Installation

About 20 mm thick stone slabs shall be fixed with cement sand grout 1:4 (1cement: 4 sand). Grout mixed with water proofing compound 4% by weight of cement and joint well grouted and cured.

External surface shall be plastered 20mm thick with cement sand mortar 1:4 (1 cement : 4 sand) mixed with 4% by weight of water proof compound and in ratio roughened.

Vertical joints shall be well cleaned and grouted to make sure it forms a continuous treatment. If required joint may be treated with sealant.

Treatment shall be taken about 300 mm above finished level.

All pipes etc. coming out of walls shall be sealed by grouting with sealant.