The Water Is Held Against the Building, Not Shed From It
On a normal site, waterproofing sheds water. Gravity does the work and the membrane job is to send water somewhere else.
Bantry Bay is built into a slope steep enough that most properties have substantial retaining structure, and behind a retaining wall the physics change completely.
Saturated soil against a buried wall creates hydrostatic pressure that pushes water at the structure continuously, from every direction, for as long as the ground stays wet. Through a Cape Town winter, when roughly 70% of the annual rain falls between June and September, that can be weeks at a time without relief.
A membrane on the inside face of that wall is being asked to hold back water under pressure, with the pressure trying to push the membrane off. It is the hardest thing you can ask waterproofing to do.
Which side the barrier is on determines everything. On the earth face, water is stopped before it enters and the pressure holds the barrier against the wall. On the inside face, the wall saturates and any weakness gets found. Where the earth face can be reached, that is the answer.
Drainage beats coating. A subsoil drain at footing level behind a retaining wall, in a stone-filled trench with a geotextile wrap and a proper discharge, relieves the pressure rather than fighting it. Many of the persistently damp lower-level rooms we are called to in Bantry Bay have no functioning drain behind the retaining wall at all, or one that silted up decades ago.
Weep holes in retaining walls exist for this reason and are frequently blocked, rendered over or never provided.
The seasonal signature is the giveaway. Damp appearing on a lower-level internal wall from June and drying out by summer is lateral water from saturated ground, not rising damp. It gets treated as rising damp routinely, and the treatment fails every time.
Podium Decks and Building Over Living Space
The second consequence of building on this slope is that Bantry Bay properties are stacked, and their outdoor space sits on top of their indoor space.
Podium decks, the terraces and parking decks built over habitable rooms, are structural slabs carrying a waterproofing system, a drainage layer and a finish. They fail like flat roofs and they leak into rooms rather than onto ground.
Pool decks and pool surrounds over living space add a permanent water source above an occupied room.
Falls and drainage layers. A podium deck needs the membrane to fall to drainage and needs a drainage layer above it that actually drains. Where paving or tiles have been laid directly on a membrane with no drainage provision, water sits on the membrane permanently.
Planters. Built-in planters on podium decks are a recurring failure point. Soil holds water against the membrane continuously and roots find any weakness. Every planter needs its own tanking and its own drainage.
Balustrade and structural penetrations through deck surfaces, each one a hole through the waterproofing.
Coastal Exposure on Top of Everything
Bantry Bay is on the Atlantic, which means it carries all of the coastal problems as well as the slope ones.
Chloride and concrete. Salt penetrating concrete reaches the reinforcement and corrodes it, and the expanding rust spalls the concrete off. Exposed slab edges, balcony soffits and parapets go first. Any membrane bonded to spalling concrete comes away with it, which is why waterproofing here can fail through no fault of the waterproofing.
Winter fronts off the Atlantic at 50 to 65kph, driving rain horizontally at the seaward elevations, terraces and glazed junctions.
Salt corrosion on every metal component, fixings, balustrade bases, gutters and brackets.
The summer south-easter, dry but strong, lifting anything poorly bonded and abrading exposed surfaces along the Victoria Road frontage.
So a Bantry Bay building can be dealing with hydrostatic pressure on one wall and driven salt spray on another, at the same time, and they need different answers.