Wet patches after rain

Wet Patches After Rain

Damp that appears or worsens in bad weather is the signature of penetrating damp.

OxfordshireDamp · Remedy · Restore

Field note

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

CSRT-accredited survey

Schematic · Plate 05

AP/DAMP

Damp that appears or worsens in bad weather is the signature of penetrating damp.

The cause

What causes it

Damp patches that appear or worsen during heavy rain and then slowly dry between showers point to penetrating damp — water finding its way through the building fabric from the outside. Common culprits include cracked or eroded mortar joints, damaged render, blocked or overflowing gutters, defective lead flashings around chimneys, missing roof tiles, and porous brickwork on exposed elevations. South-westerly walls take the brunt of British weather and often suffer first. Solid-wall properties without a cavity are particularly vulnerable, since there is no air gap to break the moisture path.

Presentation

What to look for

Look for a clear link between rainfall and the appearance of the patch — it darkens or spreads during a wet spell and fades during dry weather. The damp is often higher up the wall than rising damp would be, sometimes mid-wall around a chimney, around windows, or just below the ceiling. The affected area may feel cold and clammy, and you might see staining that follows the line of a hidden leak path inside the masonry rather than spreading uniformly.

Why it matters

If it is left alone

Penetrating damp tends to arrive in episodes but does cumulative damage. Each soaking saturates the masonry a little deeper, eroding mortar, expanding existing cracks through freeze-thaw cycles, and rotting any embedded timber it reaches. Internally, repeated wetting destroys plaster and decoration and can contaminate insulation. Catching it early, while the defect is limited to a single chimney flashing or a short run of pointing, is far cheaper than waiting until water has tracked through several metres of wall and damaged joists or lintels.

The remedy

How we treat it

The fix begins with locating the exact entry point, which often requires an external inspection at height as well as the internal damp survey. Once the defect is identified — failing pointing, a porous panel of brickwork, a leaking flashing, a blocked hopper — the external repair is carried out first to stop further water ingress. We can also apply breathable masonry creams to exposed elevations where the brickwork itself is overly porous. Internal plaster is only replaced once the wall has been allowed to dry. All works are guaranteed.

Recommended treatment

Penetrating Damp Repair

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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