Basement & Underground Tank Waterproofing

This treatment is specified where the inspection shows it is the right answer for the problem found.

Where it applies. Basements, lift pits, underground water tanks, sumps and below-ground parking — anywhere the structure holds water in or keeps groundwater out under permanent rather than seasonal pressure. Water-retaining structures are governed by IS 3370, and the tolerance for defects is far lower than for a roof. Which side we treat is decided by access: the positive (water-facing) side is always preferable, but on an existing basement surrounded by soil or a neighbouring building it is often unreachable, and then the system has to work from the negative side.

Preparation. Active water is stopped before anything else — a hydraulic plug mortar for running leaks, PU injection where water is under pressure at a crack or joint. Coating over live water is the most common failed basement repair we are asked to redo. Existing render and any previous coating are removed to sound concrete. Construction joints, the wall-to-raft kicker and honeycombed areas are cut out and reinstated with a structural repair mortar. Cracks are cut to profile. Fillets are formed at every wall-to-floor junction. Service entries are exposed and re-sealed individually. The substrate is brought to a saturated surface-dry condition — damp, not wet, not dry — because crystalline chemistry needs moisture to work and cementitious systems need it for bond.

Application. On the negative side, a crystalline cementitious slurry in two coats at right angles at the specified kg per m². Crystalline systems are used here because they penetrate and grow crystals within the concrete’s pore structure, so they resist water pushing against them rather than depending on adhesion — an adhesive membrane on the negative side is simply pushed off. On the positive side, where excavation is possible, a bonded membrane plus protection board and a functioning drainage layer backfilled correctly. Tanks receive a potable-water-approved system where they store drinking water, and this is specified explicitly on the estimate.

Curing. Crystalline systems must be kept damp for 48 to 72 hours after application while the crystal growth develops — they are moist-cured, not air-dried, and letting them dry out early is a defect. Tanks are not put into service for 7 days.

Testing and warranty. Water-retaining structures are filled and tested to IS 3370 over seven days, with the permissible drop calculated against surface area and evaporation. Basements are observed through a full wet cycle. Eligible completed work carries Leakproofs by Betterwork’s written ten-year applicator warranty on the treated area, issued after the test passes.