If you’ve had a quote for flat-roof repairs in Cape Town, you’ve probably seen the term “torch-on”. It’s the industry-standard waterproofing method for flat concrete roofs, balconies and . Here’s what it actually is and why it works.
What is torch-on waterproofing?
Torch-on is a modified bitumen membrane supplied in rolls. The installer uses a gas torch to heat the underside of the membrane as it’s rolled out, fusing it to the primed surface and to the overlapping sheet beside it. The result is a continuous, seamless waterproof layer bonded directly to the roof.
Where it’s used
Torch-on is the go-to system for flat concrete roofs, balconies and patios above living areas, parapet walls, and box gutters, anywhere water sits rather than runs off. For pitched tiled or metal roofs, different solutions (flashing repairs, sealants and roof coatings) are usually more appropriate.
Why preparation decides everything
A torch-on system is only as good as the surface under it. Proper installation means cleaning the substrate, repairing cracks, priming with a bitumen primer, and detailing corners, outlets and upstands correctly. Most torch-on failures we’re called to fix trace back to skipped preparation or poor detailing, not the membrane itself.
The protective top layer
Bitumen degrades under UV, so an exposed membrane needs protection: either a mineral-finished top sheet (the grey chip surface you often see) or a reflective coating such as silver paint. This top layer is what keeps the system alive through Cape Town summers, and recoating it periodically is cheap insurance.
How long does it last?
A properly installed and maintained torch-on system gives many years of reliable service. The keys are correct installation, UV protection, and an occasional inspection, especially of edges, outlets and upstands where movement happens.
Getting it done right
Torch-on involves open flame and skilled detailing, so it is not a DIY job. Qualispray installs and repairs torch-on systems across Cape Town as part of our waterproofing service. Book a free inspection and we’ll tell you honestly whether you need a repair, a recoat or a new system.
If your flat roof is already leaking, see our flat roof repairs in Cape Town or read more about roof repairs.