Damp and moisture meters
A resistance meter beeped on a salty chimney breast. Why can salts make that kind of meter read high when the wall is not newly wet?
Salts in the chimney breast can make a resistance meter beep when the wall is not newly wet. That kind of meter reads how easily a current passes. Hygroscopic salts from old flue deposits can pass a current without a fresh leak. The survey has a high reading on a salty breast. It has not proved a current water path, and a beep is not a decision that the chimney is wet today. The salts are the reason a high reading can mislead.
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?
Resistance meters use two pins and a small current. Masonry that holds dissolved salts conducts that current more readily, and chimney breasts often hold salts from years of flue gases. Those salts attract moisture from the air. The wall can read high on a dry week without a leak, a failed flashing or water from the stack. The beep records conductivity. It does not date the moisture or name a source. The survey should say salty breast, not fresh penetration, unless other signs support that.
A damp specialist can use a method that is less fooled by salts if you need to separate hygroscopic salt from a live leak. Do not commission injection or a new damp-proof course on the beep alone. Tell the solicitor the chimney reading is disputed by the salt explanation, so a seller's treatment quote can be checked against what was actually proved. The home survey has not proved a new leak.
What should you ask your surveyor?
- Was the high reading on the salty chimney breast specifically?
- What other signs, if any, suggested water newer than the salts?
- Have you avoided calling the beep a live leak?
What are the typical next steps?
- Keep the beep attached to salts in the chimney breast.
- Do not treat the meter alone as proof of a new leak.
- Get a salt-aware check before you agree damp treatment.
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
Would a capacitance meter avoid the salt confusion?
A different meter can be less sensitive to surface salts, but this survey used a resistance meter and got a high reading. Switching instruments was not done. Another meter would be a further visit. It is not a result you can read back into this beep.
If the breast feels cold, does that confirm new water?
Cold masonry is common on a chimney, especially on an outside wall. Temperature is not a resistance reading and it does not date the salts. The survey has not used coldness to decide the breast is newly wet from a fresh leak.