I understand why engineers in Zimbabwe default to torch-on bitumen membrane on exposed concrete decks. It has been here longer than most of us have been practicing. The workforce knows how to apply it. The quantity surveyors know how to price it. And when the application is done correctly on the right substrate, it works.
But familiarity is not the same as best practice. On trafficable concrete decks — balconies, rooftop terraces, pool surrounds, podium slabs — torch-on bitumen membrane is the wrong specification. A liquid-applied waterproofing membrane, correctly specified and applied by trained specialists, is technically superior in every meaningful way. It is time the industry recognised that.
"Familiarity is not the same as best practice. On trafficable concrete decks, torch-on is the wrong specification."
Why Torch-On Fails on Trafficable Decks
Torch-on bitumen membrane was engineered primarily as an under-screed or under-tile roofing system — a substrate waterproofing layer protected from direct exposure. When it is left exposed to foot traffic, Zimbabwe's UV intensity and thermal cycling, it degrades. The bitumen surface softens under summer sun temperatures that can push surface temps above 60°C, becomes tacky, and within two to three seasons begins to crack and blister at the seams and laps.
The standard response is to overlay a screed protection layer. This solves the traffic problem temporarily but creates a more serious long-term one. The screed inevitably cracks — it is a thin cementitious layer over a flexible membrane — and once water tracks between the screed and the membrane, it migrates laterally. By the time the leak is visible on the soffit below, the damage footprint is already far larger than the source. Full screed removal and membrane replacement follow.
A liquid-applied membrane eliminates this failure sequence entirely. Applied directly to the prepared concrete substrate, it is the finished wearing surface. There is no overlay to crack, no interface to delaminate, and no concealed path for water migration. When correctly specified — a two-component system at the correct dry film thickness with an anti-slip broadcast aggregate topcoat — it is the deck surface and the waterproofing layer in a single seamless application.
The Seamless Advantage Is Not a Minor Detail
Torch-on membrane has laps. Every lap is a potential failure point. Every penetration — drain outlet, pipe sleeve, balustrade base plate — requires a cut, a patch, a detail that relies on workmanship at the most vulnerable point in the system. On a typical 50 m² balcony deck there may be thirty or forty individual detail junctions. Each one is a risk.
A liquid-applied membrane has no laps and no patches. It flows seamlessly around every penetration and upstand, bonding to the substrate and curing as a continuous monolithic film. A trained applicator can detail a drain outlet or a pipe penetration with a liquid membrane in minutes, achieving a genuinely watertight junction that a torch-on applicator cannot replicate regardless of skill level.
"A liquid-applied membrane has no laps and no patches. It flows seamlessly around every penetration and upstand, curing as a continuous monolithic film."
Why Liquid Membrane Has Struggled Here — and Why That Is Changing
Liquid-applied waterproofing systems have developed a poor reputation on Zimbabwe sites, and I will be direct about why. The failures were almost universally application failures, not product failures.
Wrong product procured. A contractor purchases a single-component moisture-cure coating from a hardware store, applies it with a paint roller, and calls it waterproofing. It blisters within one rainy season. That is not a liquid membrane failure. That is a procurement failure. A properly formulated two-component liquid membrane, mixed at the correct ratio and applied to a prepared substrate by trained applicators, performs in a different category entirely.
Substrate moisture not controlled. Liquid membranes require a dry substrate. This is an achievable condition — it requires planning the application relative to rainfall, allowing adequate drying time and moisture-testing before application begins. Contractors who skip this step and apply membrane to a damp slab will experience blistering. Specialist contractors do not skip this step.
No primer, insufficient DFT. Applied without the correct primer on porous concrete, a liquid membrane will not bond. Applied below the specified dry film thickness, it will not bridge cracks or withstand sustained hydrostatic pressure. These are basic technical requirements that specialist contractors follow as non-negotiable procedure.
The pattern is consistent: the failures happened when liquid membrane was treated as a paint product to be applied by general labour. It is not a paint product. It is a precision-applied waterproofing system that requires trained specialist contractors — which is exactly why AIOWORX does not subcontract this work and does not allow application to proceed without proper substrate testing.
The Technical Comparison
| Performance Factor | Torch-On | Liquid Membrane ✓ |
|---|---|---|
| Seamless application | No — laps and seams throughout | Yes — fully continuous film |
| Direct trafficability | No — screed overlay required | Yes — finished wearing surface |
| Elongation / crack bridging | 40–50% | 200–300% (2-component system) |
| UV and thermal resistance | Softens and oxidises — degrades | Stable — retains properties |
| Penetration detailing | Cuts and patches — failure risk | Seamless — flows into all details |
| Application on occupied buildings | Problematic — open flame, fumes | Safe — cold-applied, low odour |
| Anti-slip finish achievable | Not directly | Broadcast aggregate in topcoat |
| 10-year guarantee achievable | Not on trafficable surface | Yes — with specialist application |
The 10-Year Guarantee Settles the Argument
At AIOWORX we back our liquid membrane deck waterproofing systems with a written 10-year guarantee. We are able to make that commitment because we control every variable — substrate assessment and testing, surface preparation, system selection, and application by our own trained technical team. We do not source products from a hardware distributor and hand them to general labourers.
No contractor in Zimbabwe offering torch-on on a trafficable deck is offering you a 10-year guarantee on the full system. A 12-month workmanship guarantee, perhaps. When the screed cracks in year two and water is tracking through the soffit by year three, you are paying for a full remediation — strip, repair, re-waterproof, re-screed. The initial saving disappears very quickly.
"The correct specification, done once, by specialists, has a higher upfront cost. It has a dramatically lower cost over the life of the building."
A Fair Concession
Torch-on bitumen membrane has its place and I will not pretend otherwise. On non-trafficable flat roofs, on below-grade retaining structures, and on large infrastructure applications where the substrate conditions favour it — it remains a robust and cost-effective solution. It is not obsolete. It is misapplied. The problem is not torch-on on roofs. The problem is torch-on on trafficable decks when a liquid-applied system is the correct specification and a specialist contractor is the correct choice.
Zimbabwe's construction sector is demanding more of its building envelope. Clients are better informed. Buildings are more complex. The expectation that a waterproofing system should last the life of the structure — not merely the defects liability period — is a reasonable one. A liquid-applied membrane, correctly specified and correctly applied, meets that expectation. It is time the specification followed the evidence.