Quick answer
A wet patch on a wall comes from an internal pipe leak, rising damp, a roof or flashing leak, or failed shower waterproofing on the other side. Temperature is the quickest discriminator: a warm patch is a hot-water line, a cool one is a cold line or damp. If the patch grows while taps are running, it is plumbing; if it grows after rain, it is the building envelope.
Common causes
- Pinhole or joint leak in a pressurised pipe buried in the wall
- Shower waterproofing failure on the other side of the wall
- Roof, gutter or window flashing leak tracking down inside the cavity
- Rising damp from below the damp-proof course, typically within a metre of the floor
- Condensation on a cold external wall in a poorly ventilated room
- Leaking waste pipe rather than a supply pipe, which shows only when that fixture is used
What you can do now
- 1Feel the patch for temperature — warm means a hot-water line and narrows it immediately
- 2Mark the edge of the patch in pencil and check in twenty-four hours to see whether it is growing
- 3Note whether it worsens when taps run, after a shower, or after rain — each points somewhere different
- 4Check the height: damp confined to the lower metre of an external wall is usually rising damp, not a pipe
- 5Photograph it as it changes; the progression tells a plumber more than a single look
When to call a professional
Book within the week to avoid mould taking hold and plaster failing. Leak detection identifies the line without breaking open the wall, which is the difference between a targeted repair and a demolished bathroom. If the patch is warm and growing, treat it as urgent — a hot-water leak inside a wall is losing heated water continuously.
Typical cost in Johannesburg
Detection R950–R1,800 · Repairs vary
Indicative ranges only. We provide written, itemised quotes before any work.
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