The damp patch on your inside wall is the end of the water's journey. The fix lives at the beginning, and finding it is the actual work. Treat the source and the patch dries for good; treat the patch and it becomes a subscription.
The usual sources, top to bottom
From above: parapet and roof edge
Damp along the top of the wall, worst after rain, often follows a failed parapet junction or roof-edge detail overhead — a roof problem wearing a wall costume (cause two).
Ledges, sills and chajjas
Horizontal surfaces collect rain and hand it to the wall below through open joints or missing drip grooves. Streak-shaped damp under a sill names its ledge.
The wall face itself
Cracked plaster, porous patches and open masonry joints drink driving rain across the whole face. Diffuse dampness appearing with wind-driven rain, drying between spells, points here.
Pipes and joints on the wall
A leaking downpipe or a joint behind it wets one vertical line, rain or shine. The pattern is the giveaway — plumbing-shaped, not weather-shaped.
From below: rising damp
A tide line in the lowest metre, salt at its edge, indifferent to rain: ground moisture climbing, not seepage descending — a different problem with a different treatment (the separation guide).
Tracing yours
- Map the inside patch: height, shape, and what sits directly outside and above it.
- Inspect that zone outside — crack, ledge, pipe, joint — in daylight and again during rain if possible; water shows its route live.
- Match the pattern: top-of-wall = above; streaks = ledges; diffuse = face; a line = pipe; tide mark = below.
Matching fix to source
- Above: repair the roof edge or junction first — wall treatment alone is bailing a boat with the hole open.
- Ledges: seal joints, form drips; small mason's work with large returns.
- Face: fill cracks, then a suitable exterior waterproofing treatment over the prepared wall.
- Pipes: plumbing repair, then let the wall dry before cosmetic work.
- Only then repair the interior — after the wall has dried through, or the fresh paint records the old moisture.
Two photographs — the patch inside, the wall outside — sent via the waterproofing page usually let us name the source in the first reply.
Frequently asked questions
The patch is damp even in dry weeks. Still seepage?
Persistent damp without rain points to plumbing or rising damp rather than weather seepage — the pattern test above separates them.
Will exterior texture paint stop seepage?
No — decorative texture resists rain on its face but does not seal a leaking wall. The order is treat, then decorate (why).