Subsidence, settlement and heave
The same crack shows on the outside brick and on the inside plaster in the same place. What does that mirror suggest, and what monitoring has not been set up?
The mirror suggests the crack may pass through the wall, rather than sitting only in the inside plaster, and no monitoring has been set up. The same crack shows on the outside brick and on the inside plaster in the same place. That match is a reason to treat it as one crack seen from both faces. It is not a measurement of whether the crack is still moving. The survey did not fit a tell-tale, did not take a dated width, and did not leave a log. The suggestion is about depth. The watch has not started.
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?
Plaster can crack on its own. Brick can crack on its own. When the lines coincide, the more serious reading is that the masonry itself is cracked and the plaster has followed. Even that reading is a suggestion from alignment, not an opening-up. The survey did not remove plaster to trace the crack and did not see the core of the wall. What is missing as well is time. One visit cannot say the crack is live. Monitoring would be a dated series. Nobody has set that series up.
Ask the surveyor to confirm the two lines are the same crack, then ask a structural engineer if the wall needs investigation or a proper watch. The solicitor should not be told that mirroring has already proved ongoing subsidence. The Association of British Insurers treats cause as something to be investigated. This report has suggested a through-crack by the match of the lines. It has not monitored it.
What should you ask your surveyor?
- Were the inside and outside cracks aligned, and how closely?
- Did you open the plaster, or only compare the two faces?
- What monitoring, if any, did this visit actually set up?
What are the typical next steps?
- Read the mirror as a suggestion of a through-crack, not as a dated watch.
- Confirm with the surveyor that the two lines are one crack.
- Ask an engineer for investigation or monitoring before naming a cause.
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 plaster crack is hairline, is the brick crack only decorative?
No. A hairline on the plaster does not make the matching brick crack decorative, and it does not set up monitoring. The survey saw the same crack inside and outside. It did not measure movement over time. Fine width on one face is still a single visit, not a record that the wall is idle.
Does matching paint make the mirror less serious?
Paint can hide edges. It does not undo the match, and it is not monitoring. The survey noted the crack on brick and on plaster in the same place. Decoration over either face was not a dated reading. The suggestion of a through-crack stands until someone investigates. A fresh coat is not that investigation.