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WATER TANKS



The leakages in water tanks can be outward from the structure, when the structure is full and inwards, when they are partially full.

Water can also seep in from the ground in case of underwater tanks.
This causes contamination of water in the tanks, and allows passage of dirt and other impurities to pass through. This may lead to health related problems, for residents of buildings.

Water is an everyday necessity, and a prime element for a living human being. Thorough inspections and professional expertise needs to be taken for handling these structures.

Procedure for Waterproofing of WATERTANKS

1. Empty the entire tank and allow it to dry for some time.

2. Clean the sides and base with wire brush to remove loose particles from the parent structure of the tank

3. Check the soundness of sides and base with the help of hammer.

4. Seal cracks, if any with suitable putty.

5. Apply Epoxy based coatings on the inside surface. For example an coating such as Waterseal ( This is tested by Haffkin Institute for Non toxicity ) can be applied on the entire surface. There should be proper ventilation, during the work, for which manholes on the top of the tanks, should be kept opened.

6. The gap between the 2 coats should be 24 hours.

7. After 24 hours of last coat, wash the tank with detergent and twice or more with water, before putting to use.

Repairs to Corrosion damages for WATERTANKS

Leakage of water and overflow of water from tank are major reasons for corrosion damage to water tanks

• Leakage can be arrested as per the method given in watertanks waterproofing section above.

• Usually, due to water vapour and chlorine present in the water, the underside of the tank top cover (not below the tank) shows severe corrosion damage. Treatment method is similar to the procedure for repairs to concrete damaged by corrosion. Additional protective coating based on acrylic base is required from underside.

• Damage to RCC walls and base slab are also attended in a similar manner.

• Provide automatic level controller to prevent overflow of tank.


Some typical guidelines and precautions to be taken related to watertanks:

• Overflow from the overhead tank should not fall freely on the terrace damaging its floor. The overflow pipe should be led to the water outlet (downtake pipe ).

• There should be suitable space between the terrace floor and the overhead tank to facilitate repairs.

• In the case of underground water tank, the ground should slope away from the tank for approximatey around 3 mts, so that the water is diverted away from the tank.

Cracks

At the sight of a crack in concrete, most of us panic.Is my house falling apart?Does the foundation need replacement?Lots of questions ? ? ? and few answers……….

Following information is intended to provide some basic reasons as to why concrete cracks and answer some of the questions.

However only a qualified technical engineer or an experienced contractor will be able to correctly analyse the cause and type of crack, and suggest the correct suitable remedy for it.

Why Does Concrete Crack?

Various forms and sizes of cracks can be seen in concrete structures.
It is important to realise that cracks as such are not necessarily defects needing repair.

Most cracks occur as a result of shrinkage of concrete.

Shrinkage is simply a reduction in the volume of concrete as it hardens.

If this reduction in volume were unrestricted, then a crack would not occur. However, in reality, ground friction and a number of things such as structural connections inhibit free shrinkage and thus cause cracks.

How much shrinkage is normal?

A 30 mtr-long regular-weight concrete slab normally would shrink by about 20 mm. In other words, you should expect cracks totaling in widths up to 20 mm in every 30 mtr of concrete.

It is important to note that concrete does crack and that this is normal. What is not normal is an unsightly and excessive amount of cracks.

Cracks can be broadly classified as either active or dormant.
If they are active, they show some movement in direction, width or depth over a measured period of time. If the cracks are dormant, they remain unchanged.

Some dormant cracks are of no danger, but if left unrepaired, cracks provide channels for moisture and water penetration, which can lead to future damage such as peeling of paint, corrosion of reinforcement etc.

Cracks can be more specifically classified based on three factors: 1) direction, 2) width, and 3) depth of the crack. They may be longitudinal, transverse, vertical, diagonal or random. They may range in size from less than 1 mm (fine) to between 1 and 2 mm (medium) to over 2 mm (wide).

A careful examination of the cracks, by a qualified engineer, will give valuable information about the cracks and will indicate their cause.

As in medicine, a good diagnosis is a must for a successful cure.

Initial investigation does not reveal all the areas of defective concrete. These investigations are done for preparing the specifications and to get an overall extent of the damage to the structure. Investigating the cause of the distress in concrete is necessary in order to recommend an appropriate repair material and strategy.

Only an experienced eye can detect a typical problem and lead to the solution for the same. Also as in medicine, a variety of repair materials are available and each has a specific use. Use of an appropriate material and technique can not only produce savings on the cost of repair, but also can ensure a durable repair.

A non-structural repair will not increase the load carrying capacity of the member nor of the structure.

Significance of Unattended Cracks:

• Leads to leakage.
• Ingress of Moisture leading to carbonation.
• Ingress of corrosive chemicals.
• Ingress of Chlorides leading to corrosion of reinforcement inside.

Some of the important needs for a satisfactory repair should be :

• All the defective concrete and the rust on reinforcement should be removed.
• All hollow & weak areas should be hammer tested and marked on surface, so that they will not be missed during repair execution work.
• Old and new concrete should have a good bond by using a suitable bonding agent.

Materials and Methods for treating cracks:



For sealing the cracks between brickwork and column or beams, which is a common problem in buildings, chip off the plaster in the region and fix a galvanized expanded (diamond shaped) mesh by nails to cover the joint with mesh 3” on either side. Then replaster.

Some cracks are caused by movement in the structure.

Repairing such cracks with epoxy could cause reoccurrence of a crack in the future at a nearby location.

Use of an appropriate flexible sealant such as silicone or polysulfide or acrylic to produce savings on the cost of repair and ensure a durable repair.

Terrace Waterproofing

Leakages in terraces, bathrooms, toilets, and walls are common problems of buildings. This will lead to dampness, which may further give rise to problems in electrical installations, fungus growth, and other unhealthy conditions for people residing there.

• Waterproofing is a skilled job and it is dangerous to get such work done from small time contractors who may not have adequate knowledge in this field.
• Other reasons like poor quality of bricks, sand, concrete, plumbing defects, etc. can lead to leakage problems.
• Materials used for waterproofing should be strictly used in same proportions and quantities, as suggested by the manufacturer or consultant.

For making more profits and save costs on these materials, many contractors often play mischief in material usage.

Terrace Leakages

The primary reason for repairing a concrete roof (terrace) is leakage in the flats below. When leakage has occurred, the first step would be to locate the potential sources for water to penetrate, which are generally junctions of the terrace with vertical surfaces like parapets and other walls.

But sources of leaks are not easy to locate and hence complete repair of the entire surface is recommended.

Bathroom & W/C Waterproofing

Leakages in terraces, bathrooms, toilets, and walls are common problems of buildings. This will lead to dampness, which may further give rise to problems in electrical installations, fungus growth, and other unhealthy conditions for people residing there.

• Waterproofing is a skilled job and it is dangerous to get such work done from small time contractors who may not have adequate knowledge in this field.
• Other reasons like poor quality of bricks, sand, concrete, plumbing defects, etc. can lead to leakage problems.
• Materials used for waterproofing should be strictly used in same proportions and quantities, as suggested by the manufacturer or consultant.

• For making more profits and save costs on these materials, many contractors often play mischief in material usage.

It is a common observation that severe leakage through the toilets and bathrooms of one flat in a building leads to nuisance to lower floor occupants.

Invariably there are no spare toilets and rectification of leakage cannot be done within a short time.

95% of the problem can be rectified without removing the tiling / pans etc.

This is because over the years of continuous usage the joints between the tile and W/C pan, joint between the pan and trap below, joints between the door frame and flooring allow the water to seep below.

Procedure to be followed is as follows:


• Take one toilet or one bathroom at a time.
• Seal all the tile joints with tile jointing mortar.
• In case of bathroom, check the nahani trap.

There is usually a gap between the jalli and the trap. This is normally plastered. There are invariably cavities in these gaps. This should be inspected. The entire cylindrical portion should be replastered with polymer modified mortar made with 1:2 cement + fine sand mortar with 15 % polymer additive by weight of cement



• For Indian W/C also the joint between S trap and W/C pan should be sealed with a suitable epoxy sealant after sealing all the tile joints with mortar.
In case the above procedure does not give results of reduction in seepage or wetness in 15 days then the entire W/C or Bathroom is required to be opened up waterproofing and tiling has to be redone. The procedure for waterproofing of sunk portion is same as brickbat coba or ferrocement waterproofing of terraces.

The floor of the WC, bathroom etc should be sloped away from the door towards the outlets.

Repair and Waterproofing - Side Walls & Chajjas (Weathersheds / Sunsheds)

SIDE WALLS
During the MONSOON it is found that there is severe leakage through side walls of buildings. Lack of rounding at the wall end of window weathershed can lead to seepage through the crack at the wall junction.
• Correct the waterproofing on all weathersheds as per sketch provided in the section below for Chajjas.
For damp patch on the wall refer to sketch 1.


• Chip off loose plaster at the brick wall. Before chipping mark the plaster patch with chalk and run a tile cutter 6” away from the outer edge of the marked patch. This helps to isolate the patch from the rest of the sound plaster. Then replaster with waterproofing material.

For beam/wall, column/wall junction type problem refer to Sketch 2 & 3.
• Fix a galvanised expanded mesh ½" x 1" diamond shape of 6" wide strip ( 3" on either side) on wall and beam with plumber nails.
• Replaster the patch with 1:3 cement sand mortar with 1% Superplasticizer. Provide a 6mm x 10mm deep groove around the repaired portion. After completing repair plaster, provide a flexible sealant in the groove to prevent the crack from reappearing.

If the leakage is between the joint of beam / brickwork or column / brickwork, the plaster in shaded portion should be removed. As seen in the picture a galvanized expanded mesh is fixed on either side of beam / column and brickwall.

CHAJJAS (WEATHERSHEDS / SUNSHEDS)

SUNSHEDS / WEATHERSHEDS show corrosion damage due to seepage of water from top through the junction between the brickwall and sunshed. Sometimes the construction is faulty with inverted pardi at the edge of the sunshed.

The accumulation of leaves, dirt and dust causes accumulation of water for days together and this leads to corrosion damage.


Repair Procedure

1. Remove inverted pardi if possible. Otherwise provide at least 3” dia PVC pipe outlet.
2. Repair soffit (bottom side of the chajja) with same procedure as for the procedure for repairs to concrete damaged by corrosion.
3. Redo waterproofing using brickbat coba method. The thickness of the coba can be 75mm near wall end and 40mm at the outer edge.
4. During the making of watta, there is a tendency to complete the work only with cement mortar. Small brick bats (pebble shaped) should be inserted in the watta slope to prevent shrinkage cracks.
5. Provide expanded mesh as shown in the figure and redo plaster. Mesh can be used when excessive damage is observed.

Staircase Waterproofing



Generally due to the method of construction of staircases in residential buildings, staircases get damaged due to corrosion very quickly.

The main reason for this is the landing / midlanding jalli work. The jalli is prone to seepage of water from rain beating side.

Many times there is no weathershed from this side. As a result, rainwater seeps through the stairway. This also gets accumulated on steps and landing (which generally do not have proper slope). It then seeps through the staircase and causes corrosion of reinforcement.

Treatment methodology is similar to the procedure for repairs to concrete damaged by corrosion. If the reinforcement is damaged a great extent, then provide wiremesh from underside of staircase while repairing.

The best long remedy is to provide weathershed (made from ferrocement) or from GI sheets / FRP sheets etc so that rain water entry into landing / midlanding is prevented.

PARKING COLUMNS

Repair of Parking Columns

Use the procedure for repairs to concrete damaged by corrosion , given in the other section of the website.
Alternatively, you can also follow the following procedure:

Strengthening columns in parking by confining with wire, meshes and fiber reinforced mortar

1. Remove plaster on columns if any. Expose the concrete surface and clean with wire brush.
2. Chase out about 5 to 6 mm deep ? 6mm wide spiral at a pitch of 75mm along the surface of the column.
3. Provide 4mm dia annealed M wire into these grooves and anchor by welding the wire by exposing existing side links at 0.50 mtr c/c and also at top and bottom end. The wire will provide additional side links. If welding is not possible then tie the wire to exposed links suitably tied with GI binding wire.
4. Provide 100 ? 100 mesh 10G weld mesh + 2 layer of ½ “? ½ “? 26 G GI hexagonal mesh over the entire column surface.
5. Apply polymer bond coat of 1 part polymer latex + 1 part water + 1.5 part cement (by weight) on prewetted column surface.
6. Apply first coat of fiber reinforced polymer mortar (like Smashtough) by quezing it through the mesh. Subsequent coats can b applied within 2 hours to make the thickness of 25mm to 30mm. The mortar is to be finished smooth to avoid replastering of columns again.
7. Cure for 7 days.

WATER TANKS



The leakages in water tanks can be outward from the structure, when the structure is full and inwards, when they are partially full.

Water can also seep in from the ground in case of underwater tanks.
This causes contamination of water in the tanks, and allows passage of dirt and other impurities to pass through. This may lead to health related problems, for residents of buildings.

Water is an everyday necessity, and a prime element for a living human being. Thorough inspections and professional expertise needs to be taken for handling these structures.

Procedure for Waterproofing of WATERTANKS

1. Empty the entire tank and allow it to dry for some time.
2. Clean the sides and base with wire brush to remove loose particles from the parent structure of the tank.
3. Check the soundness of sides and base with the help of hammer.
4. Seal cracks, if any with suitable putty.
5. Apply Epoxy based coatings on the inside surface. For example an coating such as Waterseal ( This is tested by Haffkin Institute for Non toxicity ) can be applied on the entire surface. There should be proper ventilation, during the work, for which manholes on the top of the tanks, should be kept opened.
6. The gap between the 2 coats should be 24 hours.
7. After 24 hours of last coat, wash the tank with detergent and twice or more with water, before putting to use.

Repairs to Corrosion damages for WATERTANKS

Leakage of water and overflow of water from tank are major reasons for corrosion damage to water tanks.

• Leakage can be arrested as per the method given in watertanks waterproofing section above.
• Usually, due to water vapour and chlorine present in the water, the underside of the tank top cover (not below the tank) shows severe corrosion damage. Treatment method is similar to the procedure for repairs to concrete damaged by corrosion. Additional protective coating based on acrylic base is required from underside.
• Damage to RCC walls and base slab are also attended in a similar manner.
• Provide automatic level controller to prevent overflow of tank.



Some typical guidelines and precautions to be taken related to watertanks:

• Overflow from the overhead tank should not fall freely on the terrace damaging its floor. The overflow pipe should be led to the water outlet (downtake pipe ).

• There should be suitable space between the terrace floor and the overhead tank to facilitate repairs.

• In the case of underground water tank, the ground should slope away from the tank for approximatey around 3 mts, so that the water is diverted away from the tank.

SEISMIC RETROFITTING OF BUILDINGS

Reinforced concrete is known to be a versatile, sturdy and economical construction material, especially in countries like India where the availability of structural steel is limited or expensive. A noteworthy Architectural as well as Structural advantage of reinforced concrete (RCC) is the monolithic behavior attained when proper attention is paid to concrete quality and placement. However very popularity and unmonitored use of RCC often result in poor strength, sloppy workmanship, inattention to proper detailing of critical zones in a structure, lack of provision of lateral confinement steel etc lead to serious damage to RCC structure in the event of an earthquake.

With the record of the past earthquakes in India and new research in earthquake engineering has led to modification of earthquake design code and now buildings are required to be designed for more severe earthquake than necessary 25 years back. As a result many buildings constructed before modification to codes need to be checked for new earthquake design provisions. There is thus a large number of potentially unsound buildings.

Techniques available for rehabilitation of RCC structures are numerous, and the choice of a suitable strategy is a matter of engineering judgment based on experience, damage level, structural characteristics of the building and economical considerations. Fundamental aspect of the work is the appraisal and comparison of what might be considered ‘ traditional’ methods of strengthening against earthquake such as installation of RCC shear walls, concrete jacketing of individual columns and more ‘occupant friendly’ methods involving Fiber Reinforcement and polymers.

The basic criterion in seismic retrofitting of a damaged or undamaged building is the upgradation of its resistance to increased level demanded by revised codes. Based on limitation on site, a responsible decision has to be taken about rehabilitation procedure of each structure. Repairs/ strengthening is a complex process and must be left to professionals.

Retrofitting involves Strengthening of individual members or components such as columns, beams etc by jacketing with RCC, steel angles and built up sections or externally bonded steel plates. (Refer Sketch 1)

In past few years externally bonded high strength fiber strips is becoming popular.





The walls are connected to columns and beams with steel bars anchored with epoxy. Such walls are generally located on the external periphery of the buildings. They improve strength of the lower floors – particularly the parking floor which is the most vulnerable one.

Procedure for Repairs to concrete damaged by corrosion

Typical steps followed during the repair process.
Note : The following steps ( general repair guidelines ) are to be followed during concrete repairs. Follow all instructions from the construction chemical manufacturers handbook regarding the use of the products, ex. time interval between coats, mixing, storage, health precaution of workers, cleaning of tools etc.

Step 1 - Remove loose / cracked concrete / plaster
Step 2 - Clean the steel which is exposed by wire brush
Step 3 - Application of Rust Converter
Step 4 - Application of Anti corrosive coating
Step 5 – For Cracks ( Grouting )
Step 6 - Application Corrosion Inhibitor
Step 7 - Application of Bond Coat
Step 8 - Polymer Modified Mortar
Step 9 - Plastering

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