For basements, swimming pools and underground ducts such as lift-pits, the waterproofing has to withstand the water pressure in addition to its basic stress. Shahabad box treatment method of water-proofing is very commonly used.
Carry out the work of P.C.C. bed and provide a cement mix 1:4 base coat, with water-proofing compound in the required proportion and above this fix rough Shahabad tiles of size 60 cm x 60 cm (2’0” x 2’0”) or 60 cm x 90 cm (2’0” x 3’0”) with a minimum required width of joint between the two tiles.
Ensure that all the four sides of the Shahabad tiles are cut manually to retain a fairly straight edge. Also, check the thickness of the Shahabad tiles. It should be between 32 mm to 40 mm (1 1”/4 to 1 1”/2).
Maintain the break joint pattern while fixing the Shahabad tiles for base.
After fixing the Shahabad tiles, grout the joints with cement slurry completely.
Seal the joints between the Shahabad tiles with the help of C.M. 1:3. Add some 15 mm metal to this mortar, for enhanced strength and less shrinkage.
Over this, apply a jointless layer of C.M. 1:3, approx. 25mm thick and cure it properly for 7 days. This layer provides a smooth has for the raft and protects the Shahabad base from the movement of labour and steel bars laid for raft.
Generally, all the conduiting and piping in completed before casting of the raft slab.
For basement, provision of gutter and sump is made in P.C.C., itself and Shahabad base is also prepared in the same fashion. Gutter is given proper slope towards the sump. This provision is of preventive measure against the occasional entry of rainwater in basement.
Over the plastered Shahabad base, raft slab is cast and the R.C.C. pardies are erected.
Rough Shahabad tiles are then fixed to the vertical pardi from outside. Apply neat cement paste on the four corners and in the centre of the 25 mm (1”) Shahabad tile. Press this tile firmly over the R.C.C. pardi in line and level. At one time, fix only a height of 1.0 meter. Total height of the dado, above the existing ground level, is taken as 450 mm (18”).
The joints in the vertical Shahabad are then sealed with the 1:2 cement-mortar. This is known as a pointing.
The Shahabad dado is then grouted using cement slurry with water-proofing compound. Add approximately 1 ½ bag cement in 100 litres of water, to prepare the cement slurry. Continue to pour cement slurry, every day, for three to four days, until the backside of Shahabad is completely filled with cement slurry and no more slurry is absorbed.
Cure it for at least seven days, minimum ten times a day.
After curing, provide the final jointless waterproofing plaster coat in C.M. 1:4 over the rough Shahabad.
The entire process mentioned above forms a box around the structure and does not allow any water to seep through or leak from the basement. The thickness of this treatment shall be 65 mm to 75 mm.
Shahabad Box Type Waterproofing
