The eight systems
Torch-on bituminous membrane
Rolls of APP or SBS-modified bitumen melted onto a primed concrete deck with a gas torch. The default for flat concrete roofs in Cape Town. 15–20 year service life when laid two-layer with correct 100mm side laps and 150mm upstands.
Used for: Flat and low-pitch concrete roofs, gutters, parapet detailing — see torch-on waterproofing
Liquid-applied acrylic membrane
A fibreglass-reinforced acrylic coating rolled on in three passes. Seamless, so it handles awkward penetrations and detail work well. Typically 8–12 years before a re-coat, less on a roof that ponds.
Used for: Complex roof shapes, re-coats, gutters, small areas — see waterproofing systems
Polyurethane (PU) membrane
Higher-elongation liquid system that tolerates movement and UV better than acrylic. Costs more; worth it on decks and balconies that flex and get walked on.
Used for: Balconies, decks, podiums, trafficable surfaces — see balcony and deck waterproofing
Cementitious slurry and tanking
A cement-based coating that becomes part of the substrate rather than sitting on it. Works under hydrostatic pressure, which coatings do not.
Used for: Basements, retaining walls, water features, planter boxes — see basement and cellar waterproofing
Bonded sheet membrane for wet areas
A thin flexible sheet bonded under the tile bed, taped at every corner and penetration. The only correct way to waterproof a shower — waterproofing paint under tiles is not a system.
Used for: Showers, bathrooms, laundries, kitchens — see shower waterproofing
Chemical damp-proof course (DPC) injection
A silane/siloxane cream or fluid injected into a drilled course of mortar, forming a horizontal barrier that stops capillary rise. Only treats rising damp — nothing else.
Used for: Rising damp in solid masonry walls — see damp proofing in Cape Town
Cavity drain membrane
A studded HDPE sheet that does not try to hold water back — it lets it drain to a channel and a sump. The reliable answer where the water table is high.
Used for: Basements, cellars, below-ground conversions — see basement and cellar waterproofing
Breathable façade water repellent
A penetrating silane cream that stops wind-driven rain entering porous plaster or face brick while still letting the wall dry outward. Sealing a damp wall with a non-breathable coating traps the moisture and blows the plaster.
Used for: Exposed elevations, face brick, porous plaster — see wall crack repair and façade sealing
Matching the system to the problem
| Problem | Correct system | Wrong but commonly sold |
|---|---|---|
| Flat concrete roof leaking at laps | Two-layer torch-on | Liquid re-coat over the failure |
| Rising damp in a solid wall | Chemical DPC + replaster | Damp-proof paint |
| Wind-driven rain through plaster | Crack repair + breathable repellent | Non-breathable sealer |
| Shower leaking into the next room | Bonded sheet membrane under tiles | Re-grouting the tiles |
| Basement wall wet under pressure | Cavity drain membrane or tanking | Waterproofing paint inside |
| Balcony leaking below the tiles | PU membrane + corrected falls | Sealing the tile joints |
| Water pooling against the foundation | French drain and sump | Waterproofing the wall |
Common questions
What is the best waterproofing system?
There isn't one — there is a correct system per application. Two-layer torch-on for flat concrete roofs, bonded sheet membrane for showers, cavity drain membrane for basements, chemical DPC for rising damp. A contractor who recommends the same product for all four is selling stock, not a solution.
What is the difference between waterproofing and damp proofing?
Waterproofing resists water under pressure and is designed to keep liquid water out entirely. Damp proofing resists moisture transmission through a structure — capillary rise and vapour. A DPC stops damp rising; it would not hold back a metre of standing groundwater.
How long does each system last?
Two-layer torch-on 15–20 years, polyurethane 10–15, liquid acrylic 8–12, liquid rubber re-coat 5–8, cementitious tanking effectively the life of the structure if it is not cracked, chemical DPC 20+ years. Ponding water reduces every one of these figures.