Part of Ward Property Services UK LtdPenetrating damp is rainwater finding a route through the outside of the building and appearing inside. Unlike rising damp it can show at any height, on any floor, and it characteristically worsens within hours or days of heavy driving rain and then dries back during settled weather. Surrey's exposed south-westerly elevations take the brunt of wind-driven rain, which is why the same wall of a property is often affected repeatedly.
Finding the entry point matters more than treating the stain. Water rarely appears directly opposite the defect — it tracks along mortar beds, wall ties, lintels and timber before emerging. We inspect the external envelope in detail, use moisture mapping internally and, where the route is unclear, carry out controlled water testing to prove the source before repairs begin.
Common signs
- ✓ Damp patches with irregular edges that darken after rain
- ✓ Isolated damp on upper floors or around windows and chimneys
- ✓ Staining that follows mortar courses across the wall
- ✓ Localised mould growth on one wall only
- ✓ Water marks appearing beneath a bay roof or parapet
Likely causes
- • Cracked, eroded or inappropriate cement pointing
- • Blocked, split or overflowing gutters and downpipes
- • Failed render, spalled brickwork or porous masonry
- • Defective flashings, chimney leadwork and parapet copings
- • Cavity wall tie corrosion or mortar snots bridging the cavity