Basements and cellars
A cellar has been tanked and it still smells damp. What can the survey not say about the tanking system it could not see behind the lining?
The survey cannot say whether the tanking behind the lining is sound, failed or the wrong system, because that layer was not seen. A cellar that has been tanked and still smells damp gives a smell and a lining, not a view of the membrane, the slurry or the joints. The inspection did not open the lining. It has not decided that water is crossing the tanking, sitting behind it, or arriving somewhere the system does not cover. Smell is recorded. The hidden tanking is not diagnosed.
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?
Tanking is a barrier applied to the structure, or a membrane behind a lining, intended to hold water back. Once plasterboard, render or a stud wall covers it, the surveyor sees the finish and smells the room. A musty cellar can mean the barrier is bridged, the lining is trapping damp air, or the smell is simply a closed underground room. Those causes look alike from the front of the lining. The visit cannot pick one by scent.
A specialist who tanks basements can say what would have to be opened, and at whose risk, before anyone judges the system. Do not ask the home survey to invent a failure it could not see. Tell the solicitor the tanking is concealed and the smell remains, so any guarantee the seller produces can be matched to the walls that are actually lined. The survey has not confirmed that paperwork covers this cellar.
What should you ask your surveyor?
- What of the tanking was hidden behind the lining you could not open?
- Did you record the smell without naming a failure in the hidden layer?
- Which walls are lined, and which cellar surfaces were still exposed?
What are the typical next steps?
- Keep the note as smell plus concealed tanking.
- Do not diagnose the hidden system from the smell.
- Ask for any tanking guarantee and match it to the lined walls.
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 smell is only in one corner, is the tanking only failed there?
A local smell is still only a smell. It might sit by a lining joint, a stored item or a corner that does not breathe. The survey has not seen the tanking in that corner, so it cannot place a failure there or clear the rest of the system.
Can a dehumidifier left running replace a view of the membrane?
No. Drying the air may change how the room smells on a later visit. It does not show the membrane, the slurry or the joints behind the lining. The tanking system remains unseen, which is the limit of this survey.