Below and above grade water proofing

Below-grade waterproofing

Below-grade waterproofing is applied to parts of a building below ground level (basements, foundations, retaining walls, underground tanks) that face ground water and hydrostatic pressure.

• Positive side (external): A membrane (bituminous coating, self-adhesive sheet, bentonite panels) is put on the earth face of the wall and under the raft, protected by a protection board or brick wall before backfilling.
• Negative side (internal): Cementitious or crystalline coating and plaster on the inside face.
• Integral: Waterproof concrete with admixtures, and water bars in joints.
• Drainage: Sub-soil drain, gravel layer, and sump.

Above-grade waterproofing

Above-grade waterproofing is applied to parts above the ground: exposed walls, roofs, terraces, balconies, bathrooms, parapets. These face rain and sun, but not high water pressure.

• Membranes on roofs and terraces (bituminous, PVC or liquid applied) with a protective screed or tiles.
• Brick-bat coba over slab with 1:4 mortar screed in slope.
• Waterproof paint or silicone coating on exterior walls; cement-sand plaster with compound.
• Flashings at junctions, drip moulds, and sealants at joints.

Methods to stop moisture movement in a building

1. DPC at plinth and above ground floor level.
2. Cavity wall construction.
3. Waterproof plaster and paints; pointing.
4. Roof slope, coba, membranes, flashing, gutters and downpipes.
5. Surface and sub-soil drainage; apron around the building.
6. Ventilation and vapour barrier against condensation.
7. Integral waterproofing compounds in concrete and mortar.
8. Chemical injection or pressure grouting for old walls.
9. Tanking in basements.