Damp patches on the wall — what's causing it and can it be fixed?

Damp patches are the job I get called out to most often, especially round the older terraces in Bradford, Halifax and Sheffield. The plastering bit is straightforward — but it's not the bit that matters. The bit that matters is finding out why the wall is wet, because if you just re-plaster over the top without fixing the cause, you'll be looking at the same patch again within a few months.

Here are the four main causes I see, and how to tell them apart.

1. Condensation

By far the most common. Caused by warm moist air (from cooking, showers, drying clothes indoors) hitting cold walls or windows and condensing. Usually shows up as small black mould spots, often in corners, behind furniture, or around windows. The wall itself is rarely soaked — just damp on the surface.

Fix: better ventilation. Trickle vents open, extractor fans actually used when showering and cooking, don't dry washing on radiators. Often no plastering work needed at all — just clean the mould off with a mould wash and improve airflow.

2. Penetrating damp

Water coming in from outside through a defect. Common causes: cracked render, missing pointing in brickwork, a slipped roof tile, a blocked gutter overflowing onto the wall, or a cracked rendered chimney.

Tell-tale sign: the patch appears on an outside wall, often after heavy rain, and tends to be in roughly the same spot each time. It dries out between rain spells.

Fix: find and fix the external defect first. Then once the wall has fully dried out (sometimes weeks), hack off the damaged plaster, allow it to dry, and re-plaster. Skipping the drying step is the most common mistake — it just traps moisture back in.

3. Rising damp

Actually much rarer than people think. True rising damp shows up as a tide mark up to about a metre off the floor, on ground floor walls, usually with white salt deposits on the surface. It's caused by either no damp-proof course or a failed one.

Fix: usually a chemical DPC injection by a specialist, then once the wall has dried, salt-resistant render plus a skim. This is one of those jobs where it's worth getting a proper damp survey first — a lot of "rising damp" turns out to be condensation or a leak.

4. Plumbing leak

A pipe leak behind a wall is the trickiest because it can show up anywhere. The clue is usually a patch that grows over time, or that appears on a wall behind a kitchen or bathroom. Sometimes the patch is on the ceiling below an upstairs bath or shower.

Fix: get the leak found and stopped first — a plumber or leak detection company. Then let the wall dry properly (often longer than you'd think) and we'll come and finish the wall after.

Can it be fixed?

Almost always yes — but in two stages. First, fix the cause. Second, repair the wall. I'll always come and have a look for free and tell you honestly what I think is causing it. If it's clearly a plumbing or roofing issue, I'll tell you to get that sorted first and then come back to do the plastering.

If you've got a patch on the wall and you're in Yorkshire, give me a call on 07736 467406 or message on WhatsApp.