Damp patches on walls

Damp Patches on Walls

Dark stains spreading upward from the skirting almost always mean rising damp.

OxfordshireDamp · Remedy · Restore

Field note

Category: Wall symptoms
Likely cause: Rising Damp
Guarantee: 10-year written

CSRT-accredited survey

Schematic · Plate 01

AP/DAMP

Dark stains spreading upward from the skirting almost always mean rising damp.

The cause

What causes it

Damp patches that spread upward from the skirting are the textbook signature of rising damp. Ground moisture is drawn up through the brick or stone of a wall by capillary action — the same physics that lets a paper towel soak up a spill. It happens when the property's damp-proof course (a horizontal barrier near floor level) has failed, been bridged by a raised garden bed or external render, or was never installed in the first place. Period properties built before the 1875 Public Health Act are particularly prone, since damp-proof courses were not yet a building requirement.

Presentation

What to look for

Look for a darker tide-mark band on the wall, usually rising no more than a metre above the skirting. Wallpaper may peel, paint may bubble, and skirting boards can rot or crumble at the back. The patches stay damp regardless of weather and feel cool to the touch. You may also notice a stale, earthy smell in affected rooms, especially when furniture is moved away from the wall and air starts to circulate behind it.

Why it matters

If it is left alone

Rising damp does not resolve itself. Left untreated, it migrates further into the wall, ruining plaster, warping skirting, and eventually attacking floor timbers and structural joists where they enter the wall. The longer it spreads, the wider the eventual repair, and the more likely you are to develop secondary problems such as wet rot or insect attack. Acting early usually means treating a single elevation rather than the whole ground floor.

The remedy

How we treat it

Treatment starts with a CSRT-accredited survey to confirm rising damp is the actual cause and rule out lookalikes such as condensation or a leaking pipe. Where rising damp is confirmed, we install a chemical damp-proof course — a low-pressure cream injected into the mortar bed that creates a lasting moisture barrier. Affected plaster is then removed and replaced with a salt-resistant render system to prevent the contamination behind the original plaster from re-emerging through new paintwork. All work carries a 10-year guarantee.

Recommended treatment

Rising Damp Treatment

Every treatment begins with a CSRT-accredited on-site survey, is delivered to a written specification, and is backed by a 10-year guarantee against recurrence.

Written specification 10-year guarantee

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