Barrier Waterproofing System

Barrier waterproofing places a continuous applied layer between ground water and the structure, with the intention that water does not pass through it. The layer may be a sheet, bonded or loose-laid; a liquid formed in place; a cementitious slurry worked into the substrate; or a mineral panel that swells on wetting. What they share is that the resistance is a separate thing from the structure it protects.

The product family is the least discriminating part of the approach. What decides the outcome is the substrate the layer has to bond to or span, the bond regime that governs whether water can travel behind it, the protection that has to survive backfilling and following trades, the external drainage that reduces how much water arrives, and above all the continuity at corners, laps, construction joints, penetrations and the termination above ground.

The boundary against an integral-water-resisting-concrete-system is settled by asking what is being relied on, and it is visible on site before backfilling. Here a separately applied layer does the work and the structure behind it is not required to resist water at all; in integral construction the excavation face meets bare concrete and there is no applied layer to puncture. A further, equally practical question is which side the barrier is on, because a barrier on the water-facing side is pressed onto the structure by the water it holds back, while one applied to the inside face is pushed away from it.

Being buried carries a consequence peculiar to this approach. Once backfill is placed, the layer doing the work cannot be seen, tested or reached from the side it faces. Products described as cementitious tanking slurry, pre-applied bonded membrane and bentonite panel belong here as components used within the approach rather than as approaches in their own right.

The bond regime and the detailing at laps are the same question rather than separate ones. Where a barrier is not bonded to the structure, water arriving through a defect can travel in the plane between barrier and concrete and emerge somewhere else entirely, so where a leak shows tells nobody where the breach is. Where the barrier is fully bonded, water is held at the defect and the remedy is local - which is why bond is discussed before product family.

The barrier can only be as continuous as the surface beneath permits. It cannot turn a sharp internal angle without thinning, cannot span a void it has not been told about, and cannot bond to a face that is friable, dusty or contaminated. Fillets, eased arrises and made-good honeycombing exist because of that dependency, and a substrate accepted as structurally sound has not thereby been accepted for this purpose.

Protection and drainage are dependencies that arrive after the barrier is finished, at the moment it is most vulnerable. Backfilling, compaction and site traffic all act against a completed layer nobody will see again. The drainage arrangement doubles as protection and reduces the standing water the barrier has to resist; take it away and the applied layer alone carries a demand it may never have been assumed to face.

Which side the barrier sits on changes the mechanics of every other component. On the water-facing side the barrier is pressed onto the structure and the structure resists the pressure behind it. On the inside face the same pressure works to lift the barrier off, so bond strength, the soundness of the substrate and the ability to hold the layer in compression become governing questions, and the detailing at internal corners changes with them.

The upward termination is where the below-ground barrier and the damp-proof provision above it have to become a continuous story. If the barrier stops at an arbitrary level, or laps so that it directs water inward, the buried structure can be perfectly protected while water walks in above it. Because that failure appears above ground, it is routinely blamed on a barrier that was never asked to reach there.