Damp and moisture meters
A wet plaster patch sits inside a wall that is said to be cavity-filled. Has the survey separated a leak from saturated insulation?
No. The survey has not separated a leak from saturated insulation. A wet plaster patch inside a wall said to be cavity-filled shows damp at that patch. It does not show whether rain is crossing the wall, whether fill is holding water, whether a gutter is leaking, or whether the plaster is simply cold. This visit did not open the wall, sample the insulation or trace a leak with finishes removed. The report records damp plaster and a claim of fill. It has not chosen the mechanism.
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?
Cavity fill changes how water sits in a wall. It can be wet because mortar bridges the gap, because an opening lets rain in, or because a failed gutter soaks one area. A plumbing leak can mark the same plaster. A surface reading, if one was taken, shows moisture at the face. It does not name the wet layer. The surveyor can see the patch and any obvious fault outside. Seeing those things is not the same as separating wet fill from an ordinary leak.
Tell your solicitor the cause of the wet patch was not separated. Do not order injection or the removal of fill on a guess this report has not made. If the fill is guaranteed, ask for that paper and the installer's details, and give them to someone who can investigate, perhaps by opening a small area. The survey has not named a product and has not said the cavity must be emptied. A lender should hear that damp was seen and the cause was left open.
What should you ask your surveyor?
- What defect outside lines up with the wet plaster, if any does?
- Is the cavity fill recorded as seen, or only said to be there?
- Does the report leave the cause open between a leak, bridging and wet fill?
What are the typical next steps?
- Describe the wet patch as unresolved, not as proved wet insulation.
- Ask the seller for any cavity-fill guarantee.
- Instruct an investigation that can separate the causes this visit could not.
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 tide-shaped stain prove the fill is saturated?
No. The shape of a stain is a clue. It does not sample the insulation or rule out a leak. The survey has not separated those causes. A mark like a tide line can come from more than one mechanism. Do not relabel it as saturated fill. The plaster is damp. The reason is still unsplit.
Should the cavity be emptied before the cause is known?
Not on this report. Emptying a cavity is a large step, and the survey has not shown that the fill, rather than a leak, is the source. Take fill out only if an investigation finds that the fill is what is wet. Until then, emptying would be a guess, and the plaster would still need an explanation.