Damp and moisture meters
A drip stain shows under a cavity tray only after rain, and wall ties are not mentioned. Why should those two mechanisms not be swapped?
Because one is rain at the tray and the other is metal in the cavity, and the survey has not mixed them. A drip stain under a cavity tray only after rain is water showing at the tray line when it rains. Wall ties are not mentioned, and they were not tested. Swapping the mechanisms would turn a rainwater mark into a tie failure the inspection did not record. The survey has recorded the stain and its timing. It has not decided the ties are corroding, and it has not said the tray is a tie.
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 cavity tray is there to catch water that crosses the cavity and to send it outside, usually through weep holes. A stain under the tray after rain means water is appearing on the inner face at that line: a blocked outlet, a tray with a gap, or a drip from the tray edge. Tie corrosion is expansion of metal built into the leaves, and it shows as cracking or rusting in the bed joints, not as a drip that waits for rain.
Photograph the stain and note that it follows rain, then ask a builder who understands cavity trays where that water is supposed to leave. Tell the solicitor the mechanism in the report is the tray, not the ties. Do not commission a wall-tie replacement as if this stain had diagnosed one. If a lender asks what is damp, use the survey's timing: after rain, under the tray.
What should you ask your surveyor?
- Does the drip stain sit under the cavity tray and follow rain?
- Did you mention wall ties anywhere in this note?
- Which mechanism are you actually recording, the tray or the ties?
What are the typical next steps?
- Keep the stain as a cavity-tray drip that shows after rain.
- Do not swap that mechanism for wall-tie corrosion.
- Ask where the tray is supposed to discharge that water.
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 weeps look open, can the ties still be blamed?
Not from this note. Open weeps may mean the outlet is clear, or they may not explain an inner drip. Either way the survey did not mention ties and did not test them, so the stain is not theirs to carry.
Does a dry wall in summer clear the tray?
No. A dry spell only matches the report: the stain shows after rain. Absence in dry weather does not redesign the tray, and it does not create a tie finding the survey never made. The inspection did not stretch the tray drip stain into any wider claim at all.