Wall ties and cavity insulation
On a house near the sea, rust stains the weep holes over the windows. What metal has that stain not identified, and what tie survey has it not replaced?
The rust stain has not identified which metal is rusting, and it has not replaced a wall-tie survey. Near the sea, rust at the weep holes over the windows can come from a tie, a lintel, a bead or some other piece the stain does not name. The survey has seen the staining. It has not identified the metal, has not opened the cavity, and has not carried out the tie survey that would look at the ties themselves. A stain over a window is not that investigation, and it is not a finding that the ties have failed.
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?
Weep holes are the slots where a cavity tray should let water out over an opening. Rust there means some ferrous metal is close enough to mark the mortar or the plastic. Coastal air makes unprotected steel rust more readily, which widens the list rather than naming the piece. Cavity insulation, if it is present, was not the thing being diagnosed. The home survey did not endoscope the cavity and did not test ties. Energy Saving Trust material on cavity insulation is not a tie inspection either.
If the walls need a tie opinion, instruct a specialist tie survey rather than reading the stain as one. Tell the solicitor the report has not named the metal. A lintel that is rusting is a different job from ties that are rusting, and the survey has not chosen between them. Do not let a cavity-insulation leaflet stand in for the investigation that was not done.
What should you ask your surveyor?
- Which weep holes are stained, and over which windows?
- Are you identifying a tie, a lintel, or neither?
- Did this inspection include a cavity tie survey, or only the stain?
What are the typical next steps?
- Treat the rust as an unidentified metal, not a named tie.
- Do not read the stain as a wall-tie survey.
- Instruct a specialist tie survey if the ties themselves must be identified.
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 coast is close, has the survey decided the ties are mild steel?
No. Sea air explains why bare steel can rust. It does not name the metal in these weep holes. The stain has not identified a tie, a lintel or anything else, and it has not replaced a tie survey. Coastal air is a climate, not an identification of the metal.
Does stained mortar mean the cavity insulation must come out?
No. The survey did not inspect the insulation and did not tie the stain to it. Rust at the weeps is a metal question that is still unanswered. Removing insulation is not what this note has decided. Insulation advice is a different subject from the stain over these windows.