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Hi,

I sought advice on FRP vs RCC here
viewtopic.php?f=36&t=8902&p=44220&hilit ... age#p44220

However fell for conventional wisdom and opted for RCC sump tank ,
The sump just got completed last week ( not yet plastered from inside or outside) I asked them to fill the sump before filling back the soil around walls of the tank. With around 3/4 tank full there is a seepage towards the bottom.
What is the best possible permanent fix for this ?

In hind site I think I should have gone for FRP

Technical details of the tank

The total capacity is approx 12500 liters ( 7.5 deep , 5.5 width and 10.5 feet long ) and sump was completed in 3 stages with M25 concrete with Nitobond to connect old concrete with new concrete at every joint.

First bottom was laid with M25 RMC and later walls were raised in 2 steps by site mixing as quantity was
not justified for RMC.

Concrete Mix ratio ( M25 ) However with the theoretical ratio for 1:1:2 contractor said that only jelly is being seen
and honeycombing will happen so ratio of 1:2:2 was used ( One bag Cement = 4 headpans ) so 4 : 8 and 8.
Later on my suggestion they brought 12mm jelly and 12 and 20 mm jelly stones were used in 1:1 ratio
with mix ration 4: 6: 6 or 1:1.5 : 1.5 ( retaining 25% cement in the mix)
ROFF waterproofing liquid was used as additive in the concrete

http://roff.in/roffassets/Roff-Hyproof.pdf

What is the best course of salvage from here ?

good that you have done testing of the sump before filling.
mostly masons will tell once after the plastering nothing will happen, as they have never tested the sump filling with water in their life.

ok coming to the solution part of the sump leakage,
where ever leakage is there remove the top layer of concrete (inside the sump) by half an inch and apply fidifine (Dr.Fixit) with a brush and let it dry for couple of hours.
then apply 2nd coat and let it dry again and then apply 3rd coat.
leave it for a day and then plaster that area (on the top of fidifine layers) and let it cure for 3 days and then fill the sump till the neck and leave it overnight and look for the leakages.
i have done it in the past (for many sumps) like this and and let it open for a week before filling the clay around it , there are no compilants on the sumps that i have built so far.
its is laborious process but this is the right way of doing it. if we don't take care of the sump water leakages all the water will reach the footings and you can see the cracks on the wall soon (with in months of the construction completed) as the water under the footings will make the columns weak.
let me know if u have any doubts about it.

Thanks will try pidifine 2K
Should it be applied only on leaky area or whole inner surface should be given 2 coats ?

Pidilite (Dr.fixit) has too many similar sounding products on website with overlapping roles.
I saw another one which is kind of PU coating to be applied by brush or roller.

apply only in the leaky areas, as you have already mixed water proofing liquid while concreating the sump walls its not required to apply everywhere.

Thanks a lot Ragalax the problem is fixed now followed your suggestion

Instead of Dr. Fixit used Fosroc Brushbond Rfx for plugging the joint leaks as contractor had more confidence on Fosroc product over pidilite.

Two coats done one the joints from inside and outside.
Two coats applied in perpendicular direction. After curing filled tank partially today so bottom joint got tested its not leaking.
Will fill up the tank fully next week to test for any other leaks. Tank interiors will be plastered in the end when all other work will be completed. I am thinking of applying one more layer of waterproofing in full tank from inside before plaster for added safety.

Also I found one BASF dealer nearby so purchased BASF Masterseal 551 for basement walls. Two coats will be applied from outside.

Update: tank filled till neck again and in last one week no leaks observed so gave go ahead for soil refilling around the tank.
Tank cover slab needs to be casted now and plastering from inside will be done at the time of project completion.