Chisel the extra concrete in the tank, particularly in the corners around the chambers.
Clean the entire tank, along with the bottom slab and side walls and throw away the debris.
Allow the cement slurry to penetrate all holes, cracks of bottom slab.
Check the hacking (tacha) of the vertical walls from inside for better bonding with the waterproofing.
Check the inlet, outlet and washout pipes for their rigidity. If the pipes are not rigid, grout them to achieve the desired fixity. Before grouting, check the levels of these pipes and if necessary, correct them by shifting the pipes accordingly.
Apply waterproof plaster in C.M. 1:4, by adding waterproofing compound. Apply 15 to 20 mm (1”/2 to 1”/4) metal over this plaster, particularly on the corners and base for avoiding shrinkage and to achieve better strength.
The bottom of the top slab does not require waterproofing.
The top of the overhead water tank is to be finished with brick bat coba, as mentioned for terrace waterproofing.
Allow waterproofing to set for at least 12 hours.
Cure this waterproofing for a minimum of fifteen days.
