Damp and moisture meters
Render sounds hollow and was not opened. Is that sound a detached coat, an empty cavity, or still only a sound?
It is still only a sound. Hollow render that was not opened has not been shown to be a detached coat, and it has not been shown to be an empty cavity. A tap can suggest the coat has left the wall, a void behind a patch, or simply a hard skin over a different backing. Without opening, the survey cannot say which. It recorded the hollow note. The cause stays unopened, and no mechanism has been chosen.
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?
Render is a coat applied to a wall. When it loses its bond it can drum under the knuckles, and so can a coat over an uneven dubbing-out, or a thin shell over a void. Those possibilities are not ranked by how hollow the tap felt. Opening a small area, if the owner agrees, is what lets someone see the back of the coat. This visit did not do that. Sound alone is the whole finding.
Tell your solicitor the render sounded hollow and was not opened, so no one has identified a detached coat or proved a cavity. A mason or the surveyor on a further instruction can open a patch if you need the cause named. Do not tell a lender the wall is hollow behind the render, or that the coat is loose throughout. The note is a sound at the places tapped. It is not a map of the wall.
What should you ask your surveyor?
- Was the hollow note left without an opening?
- Has a detached coat been ruled in or ruled out?
- Were only the tapped spots recorded, rather than the whole wall?
What are the typical next steps?
- Call the hollow render a sound, not a diagnosed void.
- Do not tell a lender the coat is loose throughout.
- Open a patch only if a further instruction agrees that.
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
Can hairline cracks beside the sound explain it?
They can sit next to it and still not explain it. A crack shows a line in the coat. A hollow tap is a noise. This visit did not open either place to see if they connect. Report them as neighbouring observations. Do not weld them into one cause without looking behind the render.
Does a dry meter reading cancel the hollow sound?
No. A moisture reading, if one was taken on the surface, describes dampness at that spot. It does not glue the coat back to the wall and it does not fill a void. The render was not opened. The sound remains a sound, whatever the meter showed on the face.