Subsidence, settlement and heave
What is missing when a glass tell-tale is already cracked on the day the surveyor arrives?
A baseline is missing. The broken glass shows the slip is no longer intact, but not when it broke, so if it was already cracked on arrival there is no start reading and no later reading to compare. The survey does not test the soil, and that single look cannot be plotted as a trend.
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?
A glass tell-tale is a small slip fixed across a crack so that later movement would crack the glass or shift the marks. It only works if someone records it whole and then comes back. Finding it already broken is a fact about the past, not a graph. The slip may have cracked years ago, last month, or because it was knocked. The surveyor cannot date the fracture by looking once. The Association of British Insurers describes subsidence as downward movement of the ground. A broken slip is not that measurement, and it is not proof the ground is quiet either.
Do not let a seller say the tell-tale “has done its job” because it is cracked, and do not let a buyer say it proves live subsidence. Ask when it was fixed and whether anyone photographed it intact. If those dates do not exist, the gauge has no baseline. Monitoring from today means a new gauge, or marks, read more than once. The home survey cannot be turned into the second reading of a gauge that was already spent.
What should you ask your surveyor?
- Was the tell-tale already cracked when you arrived, and did you record that?
- Is there any dated photograph of it when it was whole?
- Are you able to say the crack is live, finished, or simply unmeasured?
What are the typical next steps?
- Do not average a broken tell-tale into a storey that the house is still dropping.
- Ask the seller for any monitoring log. If there is none, say so.
- If you need a trend, instruct monitoring that starts from a known date. This visit is not that start.
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 whole tell-tale mean the wall is safe?
No. It means that slip had not broken by that day. It does not test the soil, and it does not speak for cracks that have no gauge.
Should you glue the old slip back together?
No. A repaired slip is useless as a record. Leave it, and do not pretend it can be read.