Components, systems and materials › Building components › Basement waterproofing
Basement waterproofing
What it is
Basement waterproofing is the combination of watertight structure, membranes and joint details that keeps groundwater and soil moisture out of below-ground spaces.
Where it is used
Building basements, car parks, metro stations, underpasses, lift pits, sumps and underground tanks, especially where the water table is high.
How it works
Water under pressure finds any crack, honeycomb or joint. So protection works in layers: low-permeability concrete with controlled crack widths, an external barrier membrane, sealed construction joints with waterstops, and where needed a drained cavity that collects any seepage and pumps it away. Uplift on the floor is resisted by self-weight or tension piles.
Types
- Barrier protection with external or internal membranes
- structurally integral protection using watertight concrete
- drained cavity protection with a pump sump
- combinations of these for higher grades of dryness
Materials
Dense concrete, often with crystalline or pore-blocking admixtures; bonded sheet membranes or liquid membranes; PVC or hydrophilic waterstops; drainage boards and protection boards; sealants.
The required level of dryness, from car park to archive store, and the groundwater level decide the system. The structure is designed for hydrostatic pressure and uplift, with crack-width limits suited to water-retaining concrete. Construction joint positions are planned in advance with waterstops. Penetrations for services are kept few and detailed.
Installation and QA steps
- Lower groundwater by dewatering and keep it down until the structure can resist uplift.
- Lay blinding and the under-slab membrane with lapped and sealed joints.
- Fix waterstops at construction joints and cast the raft.
- Cast walls, then apply the external membrane and protection board.
- Backfill in layers without damaging the membrane.
- Inspect for damp patches and seal leaks by injection if found.
- Leaks at construction joints and kickers
- membrane torn during backfilling
- cracks wider than the design limit
- floor uplift when dewatering stops too early
Codes cited
- IS 3370 (series) (India): Concrete structures for storage of liquids.
- National Building Code of India 2016 (India): Model code for buildings: planning, structural design, fire, construction practice and safety, building services.
Cited by number only. We do not reproduce code text, tables or figures.
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