Damp and moisture meters
Why can salts on a chimney breast be reported without anyone proving rising damp?
Old coal fires leave salts in the breast. Those salts draw moisture from the air and can keep a patch looking damp long after the flue is unused. That is not the same mechanism as water rising from the ground at the floor.
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 moisture meter will often respond on a salty breast because it cannot tell salt from free water. The patch may sit well above the skirting, sometimes halfway up the chimney, which is a poor match for rising damp. Rain can also get in at the stack and flashings and travel down the flue. A visual survey records the stain and whether the stack was seen. It does not sweep the flue or test the salts in a laboratory.
Replastering the breast without dealing with rain at the stack, or with the salts already in the plaster, can bring the mark back. Government guidance still starts with cause. Ask the surveyor whether the comment is about the chimney or about the damp-proof course at floor level. They are different repairs.
What should you ask your surveyor?
- Is the marking on the breast, at the skirting, or both?
- Did you see the stack, the flashing and the pot from outside?
- Are you treating salts as evidence of rising damp, or as a chimney problem?
What are the typical next steps?
- Do not inject the base of the wall because the breast is salty.
- Photograph the stain and the stack before the fireplace is boarded over.
- If rain entry at the stack is suspected, ask a roofer or a chimney contractor what they would open, and keep that separate from any damp quote.
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
Will boarding the breast in make the salts safe?
Boarding hides the mark. It does not stop rain at the stack, and it can hide decay in the lintel or the joists beside the breast.
Should an unused flue be closed tight?
A sealed flue can trap damp air. Ventilation of an unused flue is a separate question from the salts already in the plaster. Ask before anyone caps it solid.