Basements and cellars
If tanking stops halfway up a cellar wall, has the masonry above that line been waterproofed?
No, tanking that stops halfway leaves the masonry above that line outside the coating, so damp can show along the stop or on the bare wall above it. The coated lower half is not a certificate for the whole wall. A home survey cannot see behind either part.
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 whatever barrier was applied: a cement coat, a membrane, or a paint system people call tanking. If it ends at a horizontal line halfway up, everything above that line is ordinary cellar masonry against the ground or against damp air. Water under pressure, or salts, often appear exactly at the stop, because that is where the barrier gives up. A dry lower half does not vouch for the upper half. The surveyor should record the height the coating reaches and any mark at the junction. They should not write the wall off as tanked.
The inspection does not test the bond of the coating and does not guarantee the face behind it. A RICS home survey is visual. The Property Care Association's homeowner advice covers damp along with rot, so timber built into the uncoated upper wall still matters. Do not decorate over the stop line and call the cellar waterproof. If you need the whole wall dry, the halfway system is the thing to describe to a specialist, including whether it was meant to be a partial barrier. The survey has not supplied that design intent.
What should you ask your surveyor?
- At what height does the coating stop?
- Is there staining or salt along that line, or on the bare wall above?
- Is any timber built into the uncoated part?
What are the typical next steps?
- Do not describe a halfway coating as tanking of the whole cellar wall.
- Photograph the stop line. The height is the defect in the description.
- If you need the upper wall dry, ask a specialist about this partial coat. The survey has not certified it.
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
Is a membrane that stops halfway any better than paint that stops halfway?
It is a different product with the same limit: above the stop, it is not there. Name what was seen.
Does render above the tanking count as waterproofing?
Not unless it was described as part of the system. Ordinary render is a finish. The survey should not upgrade it.