Damp, mould & air
Condensation or rising damp? Tell them apart
One leaves a sharp tide mark with crusty salts. The other grows black speckles in corners and costs far less to put right. Telling them apart takes an afternoon, a square of kitchen foil and a walk round the outside, and it can save you an expensive treatment you never needed.
By the Tickover team · Published 9 March 2026 · 4 min read
Two very different problems
Condensation is moisture made indoors (showers, cooking, breathing, drying clothes) settling on cold surfaces. Rising damp is ground moisture wicking up through the wall itself, blocked in almost every home built since the late 1800s by a damp-proof course. Around four in five damp cases turn out to be condensation, so a rising damp verdict always deserves a hard look.
Both show up low on ground-floor walls in winter, hence the confusion. The detail separates them: where the moisture sits, what it leaves behind, and when it comes and goes.
| Clue | Condensation | Rising damp |
|---|---|---|
| Where it sits | Corners, reveals, behind furniture | Band from skirting upwards |
| Which floor | Any floor, any wall | Ground floor only |
| Mould | Black speckles, thriving | Rare on the salty band |
| Edges | Soft and patchy | Sharp tide mark |
| Residue | None | White crusty salts |
| Timing | Winter mornings, cold snaps | Steady, changes slowly |
The salts are the giveaway most people miss. Ground moisture carries dissolved minerals up the wall; the water evaporates, the salts stay, and over the years they build the crusty tide mark. They also attract moisture from the air, so a salty wall can feel damp long after the original problem has gone.
The foil test
One square of foil, one honest answer
Dry the surface
Wipe the patch and let it dry off so tape will stick.
Tape foil over it
A square of kitchen foil about 30cm across, all four edges sealed tight.
Leave it 24–48 hours
Live as normal: cooking, showers, heating on and off.
Check the room side
Beads of water on top of the foil mean condensation from the room air.
Check behind
Peel it back. Damp on the wall side means moisture coming through the wall.
Treat it as a clue, not a verdict
Both can be true at once. It narrows things down before you pay anyone.
Moisture behind the foil points to rising or penetrating damp; rain-correlation then separates those two. Moisture on the room side points at your own air, and the fix is ventilation and habits rather than builders.
Step outside
Rising damp needs a route, and the route is often visible from the pavement. The damp-proof course sits about two brick courses above ground level, a thin dark line in the mortar. Anything that bridges it carries moisture straight past.
The ground-level check
- Soil, gravel or planters piled above the damp-proof course line
- A path or patio laid higher than the DPC since the house was built
- Render carried down over the DPC to the ground
- A leaking gutter or downpipe soaking that stretch of wall
- Air bricks blocked, painted over or buried
Before you pay for anything
A free survey from a damp-proofing company is a quote wearing a lab coat. An independent damp specialist or chartered surveyor charges £150–£400, has no treatment to sell, and will tell you when the answer is a lowered flower bed or a morning ventilation routine rather than an injected wall.
And if your main symptom is mould rather than a tide mark, that is condensation talking. Deal with the growth safely (never dry-brush it), then cut off the moisture feeding it.
Want a professional answer, in writing?
Tickover Advice drafts a free, property-aware answer about your damp, and from £49 a chartered MRICS surveyor verifies and signs it. The surveyor has nothing to sell you except a straight answer.
Quick answers
How high can rising damp go?
Capillary action runs out of lift at roughly a metre above ground, which is why genuine rising damp shows as a band from the skirting to somewhere below waist height, on ground floors only. Damp at ceiling level, or patches that follow the weather, arrived some other way: condensation, a leak, or penetrating damp.
What does the foil test prove?
Tape a square of kitchen foil tightly over the damp area, leave it a day or two, then check both sides. Water on the room side means condensation from your air. Moisture trapped behind means the wall is wet from within or without. It is an indicator rather than a verdict, but it is free and surprisingly persuasive.
Should I trust a free damp survey?
Treat it as a quote, not a diagnosis. Companies that sell damp-proofing find damp-proofing problems; that is a business model, not a conspiracy. Before agreeing to injection creams or replastering, pay an independent surveyor with no products to sell, typically £150–£400, and see whether the two reports agree.
Does rising damp cause black mould?
Rarely. The salts carried up with ground moisture make that band of wall unfriendly to mould, so a crusty tide mark with little growth fits rising damp, while lush black speckling in corners and reveals fits condensation. If mould is your main symptom, look at the moisture in your air before blaming the wall.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
Keep reading
Damp, mould & airFull guide
Damp and mould: diagnose it properly first
The three kinds of damp, how to tell them apart before paying for the wrong treatment, and why most cases are condensation you can fix yourself.
6 min read
Damp, mould & air
Penetrating damp: find the way in
A damp patch that grows after rain has a way in somewhere. How to trace it from gutters to pointing, and why the inside fix always waits.
3 min read
Damp, mould & air
Removing black mould, safely and for good
How to remove small patches of black mould safely, when a bigger or recurring problem needs a professional, and the only fix that makes it stay gone.
4 min read