Age and type of house
The stone plinth under a cob wall is eroded and the cob above it is still covered. What splash-back risk is that, and what cob mix was not tested?
Rain bouncing off the eroded stone plinth is the splash-back risk, and it meets cob that is still covered. The survey has not tested the cob mix. A stone plinth is meant to throw water clear of an earth wall. Where that stone has worn back, the bounce can reach the cob instead of falling away. The report records the worn plinth and the covering above it. It has not decided that the cob is already failing, and a hidden face is not a test result.
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?
Splash-back is water leaving a hard surface and striking the wall again, higher than a drip at ground level. An eroded plinth shortens the projection that should keep that bounce off the cob. Because the cob above is still covered, the surveyor could not see staining, softening or loss in the earth itself. The mix, the straw and the depth of any damage stay unknown. The note is the stone that has worn and the face that stayed hidden.
Ask a surveyor used to cob whether the plinth should be rebuilt in a compatible stone and mortar before anyone disturbs the covering. Do not treat a damp comment as a recipe for a cement skirt, which can hold water against earth. Tell the solicitor the mix was not tested. If the hidden face must be known, that is a separate opening by someone who repairs cob, not a rereading of this visit.
What should you ask your surveyor?
- What of the eroded plinth did you actually see, and from where?
- Was the cob above the plinth left covered, and the mix untested?
- Did you record splash-back as a risk rather than as proved decay?
What are the typical next steps?
- Keep the splash-back note on the eroded plinth and the covered cob.
- Ask a cob repairer before any covering is opened.
- Do not read the report as a test of the cob mix.
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
Does a dry day show the plinth is not wetting the cob?
No. A dry visit records the weather that day, not how rain leaves the worn stone. The survey has not tested the cob mix and has not uncovered the face above the plinth. Splash-back is a wet-weather path. A quiet afternoon does not close it or prove the earth wall is dry behind the covering.
If the covering looks fresh, has the mix been named?
No. A fresh covering is why the cob was not seen. The survey has not sampled the mix behind it and has not named the earth, the fibre or the finish. Looks at the surface do not identify a cob mix. The report stops at the covering and the eroded stone plinth.