Waterproofing Questions Answered

Torch-on is a modified bituminous membrane supplied in rolls and bonded to the substrate by melting its underside with a gas torch. It is the workhorse system for flat and low-pitch roofs because it is thick, robust and forms a continuous sheet with lapped, heat-welded joints. Membranes come in APP and SBS grades: APP has better heat and UV tolerance, while SBS stays more flexible in cold conditions and handles structural movement better. Torch-on suits large, relatively simple roof areas. Its limitation is detail work — every penetration, upstand and corner has to be cut and welded by hand, so complex roofs with many protrusions often make better sense in a liquid system.

Neither is universally better; they fail in different ways and suit different roofs. Torch-on gives you a factory-controlled membrane thickness and excellent performance across large open areas, but every joint is a site-made weld and complex details take time. Liquid polyurethane is applied as a seamless coating that self-details around pipes, upstands and irregular shapes without joints, which makes it strong on complicated roofs and plant areas — but its performance depends entirely on achieving the specified thickness during application, so it is less forgiving of poor workmanship and substrate preparation. A useful rule: large, simple, accessible roofs favour torch-on; complex, heavily penetrated or irregular roofs favour liquid systems. The honest answer for any specific building requires someone looking at the roof.

Yes, but below-ground work is a different discipline from roofing because the water is under pressure rather than draining away. The critical distinction is between positive-side waterproofing (applied to the outside face, holding water out before it reaches the structure) and negative-side (applied internally, resisting water that has already entered the concrete). Positive-side is always preferable where it is achievable, which usually means during construction. For existing structures where excavation is impractical, options include internal tanking systems and crack injection to seal active leaks under pressure. Below-ground remediation almost always begins with diagnosis rather than product selection.

Crack injection forces a resin into a crack under pressure to seal it through the full depth of the element, rather than merely bridging it at the surface. Two resin families dominate: polyurethane resins, which foam on contact with water and are used to stop active, running leaks, and epoxy resins, which cure rigid and high-strength and are used to structurally re-bond a crack that is no longer moving. Choosing correctly matters — epoxy injected into a crack that is still moving will simply crack again alongside the repair. Injection is the standard approach for leaking basement walls, water-retaining structures and cracked concrete elements where surface treatment alone would not reach the source.

Yes. Alongside waterproofing, TDS installs epoxy and polyurethane floor systems including screeds, self-levelling coatings, acid-resistant coatings, high-build coatings and polyurethane spray-on systems. These are specified where a floor faces chemical exposure, heavy mechanical wear or hygiene requirements — typical in industrial, warehousing, processing and plant-room environments. Floor coatings share a critical dependency with waterproofing: almost every failure traces back to substrate preparation and moisture content rather than the product itself.

A correctly specified and properly installed system on a well-drained roof should give many years of service, and TDS backs completed work with a 10-year insurance-backed guarantee. Actual service life varies more with conditions than with the product: UV exposure, ponding water, thermal movement, foot traffic and the quality of the original substrate preparation all shorten it. Ponding is the most common avoidable cause of early failure — water that stands rather than drains will degrade almost any membrane faster than the manufacturer's figures assume. Systems that are inspected periodically and have minor damage repaired early routinely outlast neglected installations by years.

Interior staining is a late signal — by the time a ceiling shows a mark, water has usually been tracking through the structure for some time, often entering a considerable distance from where it appears. Earlier indicators are visible on the roof itself: blistering or bubbling in the membrane, cracking or crazing of the surface, lifting or open laps at joints, exposed or perished areas where the surface finish has weathered away, membrane pulling away at upstands and parapets, and standing water still present more than a day or two after rain. Deteriorating sealant at penetrations and around rooflights is another common early point of failure. An inspection before the summer storm season is considerably cheaper than a claim after it.

It depends on whether the failure is local or systemic. Isolated damage — a punctured area, an open lap, a failed detail at one penetration — can usually be repaired within the existing system, provided the surrounding membrane is still sound and compatible materials are used. Where the membrane has reached the end of its service life across the area, is widely blistered or has lost adhesion generally, patch repairs become a recurring cost that never resolves the underlying problem. An honest assessment should tell you which situation you are in, and a contractor recommending full replacement should be able to explain why localised repair will not hold.

There is no meaningful square-metre rate that applies across jobs, and any figure quoted without seeing the building should be treated with caution. Cost is driven by the area and complexity of the roof, the number of penetrations and details, the condition of the existing substrate and how much preparation or concrete repair it needs, the system specified for the exposure, access and safety requirements, and whether the building stays operational during the works. Substrate condition is the most common source of variance — a roof that needs screed correction or concrete repair before waterproofing carries costs that a visually similar sound roof does not. TDS quotes after inspection and specification rather than on a rate basis.

Rain stops most waterproofing work. Nearly every system requires a dry substrate to bond, and applying to damp concrete is one of the most reliable ways to guarantee failure through blistering and loss of adhesion. Substrate moisture content, not merely the absence of rain overhead, is the actual constraint — a roof can look dry and still hold too much moisture to coat. Winter is generally workable and in some respects preferable, since the Highveld dry season offers stable conditions, though cold slows the cure of some systems and very low temperatures affect the flexibility of certain membranes during installation. Realistic programmes build in weather contingency rather than assuming clear runs.

Usually not. Most waterproofing is carried out from the roof or externally, and commercial, institutional and industrial buildings routinely stay operational throughout — TDS has delivered facility works on occupied university campuses and operational commercial sites. Practical considerations are managed through programming: torch-on installation involves open flame and hot works permits, some liquid systems produce odour that needs to be planned around air intakes and occupied areas below, and access equipment has to be positioned safely around people using the building. These are sequencing questions rather than reasons to vacate.

Yes. TDS Contractors works nationwide across South Africa, with completed projects spanning Gauteng and KwaZulu-Natal, and undertakes work elsewhere in Africa on request. Nationwide delivery is coordinated as a turnkey package covering design, supply, installation and quality control, so the specification and guarantee position is consistent regardless of where the site is.

TDS provides a 10-year insurance-backed guarantee on completed works, alongside professional indemnity cover on the design side. The important distinction is that an insurance-backed guarantee is underwritten by a third party rather than resting solely on the contractor remaining in business — which is what gives a ten-year promise real meaning over a ten-year horizon. As with any waterproofing warranty, cover concerns the integrity of the installed system rather than damage arising from later alterations, penetrations cut by other trades, or neglect of drainage. Ask any contractor to state in writing what is covered, who underwrites it, and what invalidates it.

TDS Contractors is a member of the Master Builders Association and the Waterproofing Federation of South Africa. The company is an approved applicator for a range of manufacturer systems including Derbigum, ABE, Prostruct, Darachem and Duo torch-on systems, Poly-Seal polyurethane systems, and Sika epoxy coatings, urethane sealants and concrete repair products. Approved-applicator status matters commercially as well as technically: manufacturer-backed system warranties generally require installation by an approved applicator, so using an unapproved contractor can leave the product guarantee unenforceable.

Manufacturers issue system warranties on the assumption that their product is installed to specification, and they restrict that cover to contractors they have trained and approved. If an unapproved contractor installs the material, the product warranty is typically void, leaving you with only the contractor's own undertaking — which is worth exactly as much as the contractor's longevity and solvency. Approved status also means the installer has current knowledge of the specific system's detailing requirements, which is where most failures actually originate. It is a reasonable question to ask any contractor to evidence before awarding work.