Damp Walls: Real Causes and What Actually Fixes Them

"Damp" gets blamed for a lot of things that aren't damp. Before you spend money replastering or injecting a DPC, work out what you're actually dealing with.

Condensation (most common)

Black mould in corners, around windows and behind wardrobes. Caused by warm moist air hitting cold surfaces. Fix: ventilation, extractor fans, slightly more background heat, mould wash. Replastering on its own won't solve it.

Penetrating damp

Wet patches that come and go with the weather, usually on outside walls or under leaking gutters. Fix the external cause first — pointing, gutters, render cracks, leaking flashing — then let the wall dry before replastering with a salt-resistant system.

Rising damp

Rarer than people think. Shows up to about a metre above floor level with a tide mark and salt crystals. Needs a chemical DPC or membrane plus replastering with a waterproof render and salt-block additive, otherwise the salts pull moisture back into the new plaster.

Why replastering matters

Once a wall has been wet for a long time, the original plaster becomes contaminated with hygroscopic salts. Even after you fix the source, the old plaster will keep attracting moisture from the air. Hacking it off and replastering with the right system is what stops the staining coming back.

If you're not sure what's going on, we offer free damp assessments across Shrewsbury and Shropshire — book a visit.