Waterproofing in water tank Procedure & Type

There are two basic ways of achieving waterproofing to a substrate/ structure :

• By forming an integral barrier to water
• By filling the voids of the substrate concrete so that it becomes impervious.

By forming an integral barrier

The barrier can be formed by mixing a polymer compound in powder or liquid form to the cement and applying this blended cement in the form of slurry or mortar.

The barrier can also be formed by laying a prefabricated membrane over the substrate to have a continuous and effective barrier to water.

By filling the voids of the concrete

Filling of voids may be done by grouting polymeric or hydrophobic substance in concrete or by mixing the waterproofing product in concrete itself before placing it in position.

The product should fill up all available paths for water to flow. Hydrophobic product forms crystals when they come in contact with water and thus swells and blocks the ingress of water.
Each product or system has its pros and cons and a lot depends on the workmanship.

In general the waterproofing treatment shall be applied on the positive side i.e., on the upstream of the flow direction, unless the product is proven to be effective on the negative side. The applicator along with the product manufacturer shall give guarantee for the water tightness

Type of water proofing

1.Box Type Water Proofing Treatment for Under-Ground Structure:

Treatment below the slab :

Preparation of Surface :- On a compacted base of earth, 150 mm thic k M10 concrete pad shall be constructed to the required level and cured.

The surface of this pad should be roughened properly when the concrete is still green for the Water Proofing Treatment to adhere to the surface firmly. In case the surface is not roughened when concrete is still green, then, a bonding layer of cement slurry with waterproofing compound shall be applied over the lean concrete pad before commencing the waterproofing treatment

Preparation and laying of Blended Cement mortar course

Water proofing compound conforming to IS 2645 should then be mixed properly with the cement. The quantity of water proofing compound to be mixed should be as prescribed by the manufacturer but not exceeding 3% by weight of cement.

The quantity of cement and waterproofing compound thus mixed should be thoroughly blended and the blended cement should again be packed in bags.

For the water proofing compound in liquid form, the blending is to be done with water. This can be done by taking the just required quantity of water to be mixed in the particular batch and adding the liquid water proofing compound from sealed tins. The mixture shall be thoroughly stirred so that the water is blended with waterproofing compound properly.
Cement mortar 1:3 (1 blended cement: 3 coarse sand) shall be prepared with cement/ water duly blended as explained above.

Note :-

Only that much quantity of cement mortar which can be consumed within half an hour, shall be prepared. Any cement mortar that is prepared and remains unused for more than half an hour shall be rejected.

The lean concrete surface shall be cleaned neatly with water. 25mm thick blended cement mortar 1:3 shall then be laid to a perfect level with wooden/ aluminium straight edge of at least 2 meters long. The top surface of cement mortar should be finished neatly and later scratched when green before the base course dries and gets hard i.e., before the initial set period gets over.

(a) Laying of Kota or Other Natural Stone:

Immediately on applying cement slurry 22–25mm thick Rough Kota or other natural stone of plan dimensions, preferably 500×500 or 500×750 size, shall be laid over it and pressed gently so that the air gap are removed.

The slurry applied on the surface which gets spread when the stone slab is pressed shall get accumulated in the joints of adjacent stone slabs and if any gap still remains between the stone slabs, the same should also be filled with additional quantity of cement slurry

. For laying the stone slabs in perfect level, two stone slabs at adjacent concerns/ends shall be fixed firmly to the required level and a string stretched over the two slabs, the intermediate slabs shall then be set to the level of the string.

(b) Laying of finishing course of blended cement mortar:

The surface of stone slabs shall be cleaned and lightly watered.

Cement mortar 1: 3 prepared shall be laid over the stone slabs using 25 mm high wooden strips finishing the top surface smooth.

Before this mortar layer takes the initial set, stone aggregate of 10 mm to 12 mm nominal size shall be uniformly spread and lightly pressed into the finished surface @8 cum./sqm. The aggregates shall not be embedded totally inside the mortar and shall be visible on the top surface

Curing:

The above waterproofing treatment shall be cured for min 14 days before the RCC base slab work is commenced.

Treatment for Vertical wall

Preparing the Surface: The outer surface of the structure to be treated shall be roughed by hacking just after removing shuttering.

Alternately, the surface should be roughened by providing spatter dash key with blended cement mortar . After this apply the following process with same procedure are describe as above :-

Laying of Kota Stone

Preparation and laying of Blended Cement mortar course

Curing:

The above waterproofing treatment shall be cured for min 14 days before the RCC base slab work is commenced.

Water Proofing Treatment of Roof with APP Membrane

APP Modified Membrane is a five layered polymeric water proofing membrane with center core as of HMHDPE (High Molecular High Density Polyethylene Film), is the heart of the membrane and protects against water and moisture.

The central core is sandwiched on both sides by high quality polymeric mix with properties of high softening point, high heat and cold resistance to make it ideal for all water proofing treatment.

The polymeric mix is protected on both sides with 20 micron HMHDPE film. The membrane is available in variable thickness and weights.

Usual width is 1.0 m. The thickness and other properties of this membrane shall be as per the rainfall and the type of building. The thickness shall generally be as per manufacturer’s recommendations as different vendors have membranes varying in properties to certain extent.

Generally 2mm to 3.5mm thick shall suffice all requirements. Wherever the waterproofing membrane has to carry roof gardens over it, then it should be of special type having anti root ingress properties. Alternatively a geotextile membrane specifically made shall separate the waterproofing membrane and the garden soil.

Preparing the Surface:

The surface to be treated shall have a slope of minimum 1: 120 given either in the structure or done using brick bat coba as per clause 5.

The graded surface of the roof, fillets and the faces of walls shall be thoroughly cleaned with wire brushed and all loose scales etc. removed. The surface shall then be dusted off. Any crack in the roof shall be cut to V section, cleaned and filled up flush with non-shrink grout or blown type petroleum bitumen of IS grade 85/25 of approved quality conforming to IS 702.

Application of Primer:

The primer shall be blown type bitumen conforming to IS 702 or residual bitumen 85/25 conforming to IS 73 applied @ 0.4 liters per square metre of the surface area.

The primer shall be brush applied on all surfaces and corners including the flashing groove in parapet walls and all such surfaces which are to be covered by membrane waterproofing. The primer shall be allowed to dry for 24 hours

Laying of APP membrane

The roof surface shall be cleaned and dried thoroughly. The drain pieces shall be installed before commencing the membrane laying work. The APP modified polymeric membrane shall be cut to the required length, brushed clean of dust and loose material and laid out flat on the roof to eliminate curls and subsequent stretching. The membrane shall be laid in length perpendicular to the direction of the slope and laying shall be commenced at the lowest level and worked up to crest. The membrane shall not be laid in single piece of very long lengths as they are likely to shrink; 6 to 8 m are suitable lengths.
Each length of membrane shall be unrolled in position and rolled up for a distance of half its length. The membrane shall be torched as per manufacturer’s specifications and laid on the surface and pressed to remove all air bubbles. All longitudinal laps shall be minimum 75mm and all end laps shall be min 100mm. Water proofing treatment shall be carried into the drain pipe and other outlets by at least 100 mm.
APP waterproofing membrane shall be laid as flashing wherever junction of vertical and horizontal surfaces occur such as at the junction of parapet wall and slab. The flashing longitudinal laps shall be 100 mm. The upper edge of flashing membrane shall be well tucked into the flashing grooves in the parapets etc. The groove shall be sealed with the approved sealant or cement concrete after terminating the membrane.
Where parapet walls are of height 450 mm or less the water proofing membrane flashing shall be continued for the full height of the wall and taken right across the wall top and ended on the outer face of the wall with a minimum distance of 100mm.
Where low dividing walls or inverted beams are met with, the same treatment shall be continued over the vertical and horizontal portions of the same to the other side. Drain outlets formed in such walls/ inverted beams shall be given same treatment as for the vertical down take pipes.
At locations of expansion joints, the membrane shall be continued over the fillets and then the dwarf walls and ended on the vertical face of the dwarf wall from both sides. A separate membrane shall be run over the cover slab horizontal portion and taken down to its vertical face and ended there. The membrane should be laid longitudinally over the cover slab to minimize joints in the membrane.

Membrane Protection:

If the roof is accessible then the membrane shall be protected by laying a 25mm thick concrete screed of grade M15 with 12mm down aggregates. The screed should be properly leveled, compacted and cured as per standard practice. The screed should be finished with a groove pattern of 300mm x 300mm and 8mm deep done when screed is green. Alternatively, if Architect recommends, the membrane may be protected by laying tiles of required colour and finish on a cement mortar (1:4) of 20mm thick.

Waterproofing by Liquid Coating:

Surface Preparation:
The surface shall be prepared and given slope in the same manner as done for membrane waterproofing.

Application of Primer :Suitable primer as recommended by the manufacturer of liquid coating shall be applied and the surface shall be allowed to dry thoroughly.

Application of Liquid coat:Application method shall generally be as specified by the manufacturer. However, in absence of any such recommendation, the following method shall be adopted:
First coat of liquid waterproofing compound shall be applied by brush for a minimum thickness of 0.5mm but for an overall thickness of 1.0mm over the primed surface. Subsequent coat of similar thickness shall be applied when the previous coat is set but still tacky. The treatment shall be allowed to dry completely before proceeding with next layer.

Protection Layer:
Protective layer similar to membrane waterproofing shall be provided.

Waterproofing Treatment to Sunken Portion of WC, Kitchen etc:

Preparing Surface and Fixing Pipes and Fittings

Before the water proofing treatment work is taken up, proper key in the concrete surface should be provided. The depressed/ sunken portion should be hacked by a hacking tool, after the concrete slab is cast and when this concrete is still green. In case of old work not hacked, the water proofing treatment on such surfaces shall be permitted after making proper spatter dash key.
Fixing the ‘P’ trap in position and all other pipes work including the water escape pipe shall be fixed properly and the holes should be plugged carefully before taking up the water proofing work.
The depressed/ sunken portion of WC shall be cleaned of all debris, extra mortar sticking to the vertical and horizontal surface etc.

Preparation and Application of Cement Slurry

Cement duly blended with water proofing compound as explained in 4.1.3 shall be used for preparing the cement slurry. The consistency of the slurry should be such that 4.4 kg of blended cement with water proofing compound is used per sq. metre area of surface to be treated. The slurry should be applied starting from the vertical faces towards the bottom of the floor. Particular care should be taken to see that the slurry is applied to corners without leaving any gap.

Preparation and Application of Cement Plaster:

Immediately on applying the blended cement slurry on the surface to be treated cement plaster 20 mm thick in CM 1:3 (1 blended cement: 3 coarse sand) shall be applied both on vertical and horizontal surfaces taking particular care to complete the entire depressed/ sunken portion of WC within a day so that the plaster work is done without any joint. Junctions shall be properly rounded. The surfaces of the plaster shall be left rough but finished in one plain and cured for a week.
On completion of the curing period both horizontal and vertical surfaces shall be cleaned properly and gently and allowed to dry.

Application of Bitumen:

After the surface is completely dried blown or residual bitumen shall be applied @ 1.7 kg of bitumen per sqm area.

Application of PVC Sheet:

PVC sheet 400 micron thick shall be spread evenly without any kink immediately over the bitumen so that the PVC sheet sticks to the surface firmly. PVC sheet shall be continued over the main slab horizontal portion for about 100 mm. Joints of PVC sheet should have minimum overlap of 100 mm by pasting the overlapped sheet with an application of bitumen @ 1.7 kg/ sqm. Instead of bitumen and PVC sheet liquid coating system as described in 9 may also be used.
The projections of pipes and ‘P’ trap outlet etc. inside the depressed/ sunken portion shall also be cladded with water proofing treatment layer up to a height of 150 mm, using a coat of bitumen with PVC sheet or liquid waterproofing coating complete. The depressed/sunken portion shall then be filled with specified filling material and base concrete.

Tiling:

Waterproofing treatment of bitumen & PVC sheet or Liquid coating as explained above above shall again be provided over the base concrete. Cement plaster shall be provided over it as described in 10.3 above. Tiles shall be laid over this to required slope.

Damp Proof Course (DPC)

Damp proofing courses shall be generally used in brick walls to arrest the capillary rise of sub soil moisture to superstructure walls. This course is laid on the brick work at the outside grade or paving level. Damp Proof Course shall be constructed with 150 mm thick M20 grade concrete with liquid based water proofing admixture manufactured by reputed manufacturers per their product recommendations. Above this, the superstructure brick work shall be constructed. DPC shall extend through the full thickness of the wall, including pointing, applied rendering or any other facial material. Where the DPC is to be laid on a hollow block wall the blocks shall be filled with cement mortar for the course below the DPC.