The two systems that work
| Cementitious tanking | Cavity drain membrane | |
|---|---|---|
| Principle | Resist the water | Manage the water |
| Method | Multi-coat cement slurry bonded to the structure | Studded HDPE sheet, drainage channel, sump |
| Needs a sump | No | Usually yes |
| Tolerates movement | Poorly — cracks if the structure moves | Well |
| Reversible | No | Yes, and inspectable |
| Finish | Plaster directly onto it | Battens or a dry lining over it |
| Indicative | R600 – R950/m² | R750 – R1,200/m² |
On a structurally sound, non-moving wall with moderate water, tanking is cheaper and gives a usable plastered surface. Where the water table is genuinely high, where the structure moves, or where a failure would be expensive to discover, cavity drain is the more honest system — it does not depend on being perfect.
Getting the outside right first
Almost every basement problem is made much cheaper by dealing with the water before it reaches the wall. Where the site allows it, that means a perimeter french drain at footing level, surface water directed away from the building, and downpipes discharging into stormwater rather than against the foundation.
Internal tanking on a wall that has a downpipe emptying against it outside is money spent in the wrong order.
Common questions
How much does basement waterproofing cost in Cape Town?
About R600–R950 per m² for cementitious tanking and R750–R1,200 per m² for a cavity drain membrane system. A sump and pump installation adds roughly R8,000–R20,000.
Can I just paint the inside of my basement wall?
Not against hydrostatic pressure. Water pushing from the negative side will lift a surface coating off the wall — the coating has nothing but its own adhesion resisting the pressure. This is the most common failed basement 'repair' we are called to replace.
What is negative-side waterproofing?
Treating the inside face of a below-ground wall, i.e. the side opposite the water. It is what you do when you cannot excavate to reach the outside. It works, but it demands a system designed for it — cementitious tanking or a cavity drain — not a coating.