Basements and cellars
Tanking stops part-way up a basement wall and the plaster above it is marked. What height of wall was not covered?
The height of wall above the tanking was not covered. The system stops part-way up, and the plaster on that upper band is marked. The survey has recorded the stop line and the marks above it. It has not measured a guaranteed dry zone, and it has not decided whether the marks are salts, condensation, or water getting past the top of the tanking. Everything above the stop sits outside the covered height. The survey has not specified extending the system, and it has not said the covered part below the line is a proved success.
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 put on a basement wall to resist moisture from the ground side. Where it stops, the masonry above relies on ordinary plaster and on whatever resistance the wall itself has. Marks in that plaster can be old decoration, salts, or moisture at the unprotected band. The survey can see the line and the marks. It cannot see how the hidden edge of the system was finished. The upper band is simply not covered.
Tell the solicitor the tanking is part-height and the plaster above it is marked, and ask what paperwork exists for the system. A specialist can be asked, separately, whether that stop is intentional. The survey has not written a specification and has not tested the wall. Do not treat the marks as proof the whole basement has failed, and do not treat the covered height as certified. Both of those decisions sit outside this note.
What should you ask your surveyor?
- Where does the tanking stop on this basement wall?
- What marks did you see in the plaster above that line?
- Have you left the uncovered height outside any claim that it is tanked?
What are the typical next steps?
- Treat only the wall below the stop line as covered.
- Ask the solicitor for any tanking paperwork.
- Do not read the marks above the line as a certificate either way.
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 lower wall looks dry, is the stop line in the right place?
The survey has not decided that. Dry plaster below the line, on the day, does not prove the stop was designed correctly, and marks above do not by themselves prove the tanking has been overtopped. The uncovered height is simply not covered. Where the system should end is a specialist question, not a finding this report has made.
Should the whole basement be retanked because the upper plaster is marked?
Not on this note. The survey recorded a part-height stop and marks above it. It has not specified a new system for every wall. Marks on the uncovered band are a reason to ask what that height is doing. They are not an instruction to strip the room.