Repair or Redo, Decided on the Roof
Most flat roofs that leak do not need a new membrane. They need the one failure that is letting water in found and fixed properly.
Torch-on and liquid membranes fail at predictable points. A lap that was never fully bonded. An upstand where the membrane stops short. An outlet. A split where the deck moves. A puncture where someone crossed the roof with a ladder. If the membrane around that point is still flexible and well bonded, a repair lapped onto sound material is the right answer and lasts as long as the rest of the roof.
It stops being the right answer when the membrane is failing everywhere at once. Cracking across the open field, widespread blistering, moisture trapped under large areas, or a roof that is now more patch than membrane. Patching that roof moves the leak from one place to the next.
We tell you which yours is, including when the honest answer is the smaller job.
The Flat Roof Repairs We Do Most
Split and lifted laps. Cut back, dried, primed, and re-lapped onto sound membrane.
Upstands and parapets. The membrane re-dressed up the wall to the correct height, with the top edge properly terminated so water cannot get behind it.
Outlets. Cleared, replaced where perished or undersized, and the membrane re-dressed into them.
Blisters. Cut out, dried and patched where they have split or are spreading.
Punctures and cracks from foot traffic, plant installers and dropped tools.
Failed old patches. Earlier repairs bonded over dirt or onto wet screed, which come away and have to be removed before the real repair can be made.
Why Flat Roof Patches Fail
A patch is only as good as what it bonds to. The patches that fail were usually stuck onto a dusty, damp or degraded surface, or laid short so they barely overlap the good membrane around them.
Moisture is the other reason. Water that has been getting in for a winter sits in the screed under the membrane. Seal a patch over it and the sun drives that moisture back up as vapour, lifting the patch from below. Where the screed is wet, it has to dry or be cut out first.
And a repair where water stands for days after rain is fighting the roof. Where the falls have been lost, we point it out and price it separately, so you can decide.
Flat Roofs and the Cape Town Front
A cold front drops a lot of water in a short time, on a north-westerly wind at 50 to 65kph. On a flat roof that does two things. It tests outlet capacity, so a partly blocked outlet backs up and water rises toward the top of the upstands. And it drives rain sideways into the parapets, which is where upstand repairs earn their keep.
The south-easter does its damage in summer, lifting loose lap edges and blowing grit into outlets.
Repairs that need a dry deck belong in the dry months, ideally March or April, before the first front of winter.
