BOX TYPE WATERPROOFING FOR UNDERGROUND TANK

Box type waterproofing for underground tanks

Procedures for Box-type Water-proofing for Underground Water Tanks:

Pre Waterproofing Procedures:

1)             Ground shall be excavated at least 750 mm beyond the external faces of the walls of RCC tanks, the additional excavated space acting as working space.

2)          If water table already exists within the excavated area, then the excavated area shall be kept sufficiently dry by creating a bund all rounds.

3)          Bund shall be created with the help of sand bags filled with puddle and gaps between sand bags being filed with puddle.

4)           The area shall then be dewatered using a dewatering pump of suitable capacity ranging from 2 Hp to 5 Hp depending upon amount of water to be removed.

5)         Shahabad stones received on site shall be cut and dressed to correct sizes as required.

6)         Shahabad stones shall be soaked for 2 Hours before fixing.

During Waterproofing Procedures:

1)     It shall be ensured that the excavated pit is sufficiently dry before laying PCC and all the raw materials is made available.

2)    PCC proportion as mentioned on drawing shall then be laid on the ground. Thickness of PCC shall be as per drawing.

3)    Care shall be taken so that PCC is laid in perfect level without slope.

4)    PCC extends at least 150 mm beyond the vertical faces of base slab. PCC shall be cured for at least 3 days.

5)    Over PCC, 20 mm thick layer of cement sand mortar (1:4) well mixed with water proofing compound shall be laid over the entire surface of PCC.

6)      Proportion of water proofing compound shall be as recommended by the water proofing compound manufacturer.

7)    Mortar shall be preferably mixed in mechanical mixers and unloaded in MS tray and shall be used within 1 hour of preparation.

8)    Next day cement slurry is spread over water proofing layer and Shahabad stones are laid side by side over it

with 10-15 mm gaps between the stone slabs by applying a layer of water proof mortar on backs. Mortar proportion shall be as mentioned in drawing or as specified by QA Department.

9)    Gaps between stone slabs shall be filled with cement sand mortar (1:4) with water proofing compound or as specified in drawing.

10)     Laying of Shahabad stones shall be done over the entire surface of water proofing layer laid earlier.

11)      Next day joints between stone slabs shall be raked to a depth of 15 mm and grouted again with the fresh mortar.

12)     Over the stone slabs, 20 mm thick layer of cement sand mortar (1:4) mixed with water proofing compound shall be laid over the entire surface of stone slabs laid. 12 mm downgraded aggregates shall be placed at random in this layer.

13)     This layer shall be cured for 3 days before starting construction of RCC base slab and walls. RCC base slab and walls shall be constructed monolithically and as per dimensions mentioned on the drawing.

14)       Water proofing layer shall also be applied on top of the projected portion of base slab and cured as specified.

15)      Water proofing of tank walls shall not start unless tank walls are constructed to their full height and well cured for at least 7 days.

Water Proofing over side walls:

1)            A groove of width equal to thickness of Shahabad stones shall be made to the full depth of top water proofing layer below RCC base slab as also over top of projected portion of base slab.

2)           Groove shall be made with the help of round wheel cutter at a distance of 15-20 mm from external face of base slab, all along the periphery of RCC tank.

3)         Within the groove Shahabad stones shall be fixed side by side without leaving any gap between edges.

4)         At a time not more than 3 horizontal layers of stone slabs one above other shall be laid.

5)            Gap between vertical slabs being laid and tank walls shall be maintained

6)            with the help of suitable steel spacers, if required, for the purpose of suitability of vertical stone wall being laid.

7)           After the vertical stone wall is erected, the external face of wall shall be applied with 8 mm thick rough cement sand plaster and cured for 2 days. Enough roughening of this plaster shall be done when the plaster is green.

8)           Gap between stone wall and RCC tank wall shall then be filled with cement sand mortar (1:4) mixed with water proofing compound. Care should be taken so that hollow pockets are not formed behind the vertical stone wall.

8)     This sequence of erection of stone wall shall continue till the required height. (Minimum at least 300 mm above ground level)

9)    After erection of stone wall, the external rough surface of stone wall shall be applied with finishing coat of 15 mm thick cement sand mortar (1:4) and cured for 3 days before backfilling starts.

Post Waterproofing Procedures:

1)    Backfilling shall start after satisfactory curing of finishing coat on external water proofing.

2)     Backfilling shall be done with murum or good quality earth in layers of 300 mm thk which are adequately watered and compacted with rammers.

Acceptance of Completed Work:

Type of check	Acceptance
Side water proofing provided	At least 300 mm above ground level
Base water proofing provided	At least 150 mm beyond the external face of RCC walls
Finished coat over vertical Shahabad tiles	In plumb, and corners finished properly