Start with what you can see. This is an index, not an essay: find the symptom that matches your building, read the likely causes, and follow the link to the article that deals with it. Diagnosis before products — always.
Find your symptom
| What you see | Usually means | Go to |
|---|---|---|
| Damp patch on a top-floor ceiling, worse after rain | Roof defect above | Why roofs leak |
| Damp on a ceiling below someone else's flat | Their bathroom or plumbing | Leaks from the flat above |
| Damp patch on an internal wall, rain-linked | Exterior seepage | Tracing wall seepage |
| Tide line low on the wall, with salt | Rising damp | Rising damp explained |
| Damp at the base of a wall, no tide mark, only after rain | Splash-back or drainage | Treating a damp wall |
| Damp in closed rooms, corners, winter | Condensation, not seepage | Dampness vs leakage |
| White powder or crystals on masonry | Efflorescence — water moving through | Salt patches explained |
| Paint blistering or peeling in sheets | Moisture behind the film | Reading the failure |
| Black spots, musty smell | Surface moisture, often condensation | Dampness vs leakage |
| Water stands on the roof after rain | Drainage and falls | Roof sequence |
| Hollow or lifting terrace tiles | Water under the finish | Terrace sequence |
| Damp on the wall below a balcony | Threshold or junction | Balcony guide |
| Damp below a bathroom | Four possible causes — test before opening the floor | Narrowing it down |
| Damp in a below-ground room | Ground water pressure | Basement guide |
| Cracks — hairline maps or wide lines | Thermal, or structural | Telling them apart |
| Rust stains bleeding from concrete | Water has reached the steel | Structural assessment — ask us |
The three rules behind every row
- The stain is the exit, not the entry. Water travels inside structures and emerges at the weakest point.
- Treat the cause, not the symptom. Sealing an exit moves the problem; it does not end it.
- Dry before you decorate. Fresh paint on a wall that has not dried through records the old moisture within a season.
When to send photographs instead of guessing
If two rows above could describe your case, or the damp does not sit under anything obvious, photographs settle it faster than reading. The patch inside, the surface outside or above, and your city — sent through the waterproofing page. A first opinion costs nothing and often saves a wasted purchase.
Frequently asked questions
Can one wall have two problems?
Often — a monsoon leak and winter condensation on the same wall. Each needs its own remedy.
Which symptom is most urgent?
Rust staining. Everything else damages finishes; that damages structure.