Basement Water & Groundwater Ingress

What causes it

Standing water, wet floors and white salt bloom in basements, driven by groundwater pressure against the structure.

A basement is the one part of a building where water pressure is permanent rather than seasonal. A terrace is loaded three months a year; a basement wall below the water table is loaded every day. That changes what fails and what works.

• The kicker joint between raft and walls — the classic failure, where a waterstop was omitted, displaced during the pour or lapped wrongly.
• Construction joints and honeycombing from poorly compacted pours, which leak in a straight line along the joint.
• Service entries sleeved but never sealed — pipes, cables and conduit passing through a wall that is holding back groundwater.
• Lift pits and sumps, which sit lower than everything else and therefore see the greatest head.
• Ramps and the transition where a podium or parking deck above meets the basement structure.
• A previous internal coating that has blistered and peeled — applied on the negative side, where water pressure pushes it off the wall rather than holding it on.

Damp smell without visible water usually means vapour transmission through the slab or walls rather than a discrete leak, and it is treated differently.

How we identify the real source

Water travels. The stain on a ceiling is frequently metres from the actual point of entry, which is why we deep-scan the structure before recommending treatment rather than working from the visible damage alone.

How we treat it

Active water is stopped before anything else. Coating over running water is the most common failed basement repair we are asked to redo — a hydraulic plug mortar for a running leak, or PU injection where water is under pressure at a crack or joint.

Which side we treat is decided by access. The positive, water-facing side is always preferable, because pressure then holds the membrane onto the structure instead of pushing it off; that means excavating outside and applying a bonded membrane with a protection board and a properly reinstated drainage layer. Where excavation is impossible — a neighbouring building, a road, a boundary — the answer is a crystalline cementitious system, which penetrates the concrete and grows crystals within its pore structure so the concrete itself becomes the barrier. It does not depend on adhesion, which is precisely why it works from the negative side.

Preparation matters more here than anywhere: previous coatings removed to sound concrete, joints and honeycombing cut out and reinstated with a structural repair mortar, fillets formed at every wall-to-floor junction, service entries re-sealed individually, and the substrate brought to a saturated surface-dry condition.

Crystalline systems are moist-cured, kept damp for 48–72 hours while the crystal growth develops — letting them dry early is a defect. Water-retaining structures are then tested to IS 3370 over seven days, and basements observed through a full wet cycle, before the warranty certificate is issued.

What it costs

Use the cost calculator for an indicative range, or book a free inspection for a written estimate.