Damp and moisture meters
A tide mark shows only where a skirting was removed, and the plaster above is dry. Why is that line not, on its own, a diagnosis of rising damp?
The tide mark behind the removed skirting is not, on its own, a diagnosis of rising damp. It is a line that appeared where the skirting came off, and the plaster above that line is dry. A line at the skirting is a reason to investigate. It does not prove moisture is rising from the ground. A moisture meter is only an aid, and foil-backed board can mislead a pinless meter if that was the surface read. Keep the mark as an observation.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
A line like this is easy to over-read because it looks like a waterline. This one is limited to the strip the skirting hid, with dry plaster above it. That can be an old mark, a local leak, or salts left in the surface. The survey did not claim a measured rise, and nobody should invent one now. No height belongs on this line.
Ask what else was there: salts, a bridged course, high ground outside, or a dry base along the wall. Each of those is its own observation. None of them, and not this line alone, proves rising damp. Putting the skirting back would hide the mark without answering it. Investigate the base of the wall before anyone names a cause.
What should you ask your surveyor?
- Was the tide mark only where the skirting came off, with dry plaster above?
- Did you see salts, bridging or high outside ground at the same spot?
- Are you keeping this line as an observation rather than a diagnosis?
What are the typical next steps?
- Do not write the hidden line up as rising damp on its own.
- Photograph the mark before the skirting is fixed back in place.
- Investigate the base of the wall before you name a cause for the line.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the plaster above is dry, is rising damp ruled out?
Not ruled out, and not confirmed. Dry plaster above means this line on its own is not a diagnosis. The base of the wall still needs its own look.
Does the height of the mark show how far damp has risen?
No. The survey did not measure a rise, and a height should not be invented. The line is only where the skirting was removed.