Basement waterproofing protects below ground spaces from groundwater, seepage and ground moisture. One question determines how the solution is designed: can the outer face of the wall be reached?
Positive and negative waterproofing
Waterproofing applied to the face the water comes from is called positive. Applied to the outside of the wall it is positive and always more durable. Where the outer face cannot be reached, the work is done from inside, which is called negative waterproofing.
Bituminous membrane cannot be used on the negative side. Water pressure separates the membrane from the substrate and the system fails within months. On the negative side, crystalline systems or two component cementitious coatings are used.
External application
The ground is excavated down to the base of the wall and the surface is cleaned and repaired. After priming, two layers of bituminous membrane are laid with staggered laps. A drainage and protection board goes over them, and a perforated pipe wrapped in filter geotextile is laid at the foot of the foundation. Backfill is placed and compacted in layers using screened material.
The waterproofing must run at least thirty centimetres above ground level and be mechanically terminated at the top. Otherwise surface rain and splashback enter where the waterproofing stops.
Internal application
Any active flow is first cut off by injection. The surface is then prepared and made good with repair mortar where needed. A crystalline system or cementitious coating is applied. Wall to slab junctions, pipe penetrations and corners are resolved with separate detail products.
Where the water load is high, surface waterproofing alone is not enough. A collection channel and pumping chamber at the foot of the wall inside the basement reduce the pressure.
From symptom to cause
Damp increasing after rain and stopping in the dry season: missing drainage.
Damp all year round: water table above wall level.
Horizontal band at ground level: waterproofing not carried high enough.
Isolated patch: mechanical damage during backfill.
Damp concentrating on cold surfaces in winter: may be condensation rather than a leak, ventilation should be assessed.
Frequently asked
Is there a solution if excavation is impossible
Yes. A combination of injection, negative side waterproofing and internal drainage is used. Durability requires all three to be considered together.
Do paint type products work
They hide surface damp temporarily but do not resist water pressure. They blister and peel within a short time.
Is waterproofing enough on its own
Not while the water load continues. Waterproofing installed without drainage to reduce pressure wears out before its design life.
An on site inspection to establish the source of the damp is decisive in choosing the right method.