Damp and moisture meters
The surveyor tapped the render and called one patch hollow. What has that tap not proved about the brick behind the coating?
The tap has not proved the state of the brick behind the coating. A hollow sound on one patch means the render there is not stuck fast to whatever is behind it. The survey has recorded that sound at that patch. It has not opened the coating, so it has not seen the brick, and it has not decided whether the face is sound, soft, damp or already loose. Hollow render is a bond between coating and background. It is not a test result for the masonry the tap could not reach.
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 light tap tells you about the coating. A drum-like note usually means a gap or a loss of key, so the render has parted from the wall in that patch. The brick may be dry and firm, or it may be the reason the render let go, and the tap cannot choose. Moisture can sit in a hollow patch because water tracks behind loose render. That is still a comment on the coating. It is not a diagnosis of the brick, because the brick was not exposed.
Ask the surveyor how large the hollow patch was and whether it lined up with a crack, a gutter or the base of the wall. If the render must come off to see the brick, that is opening-up, not something this tap already did. Tell the solicitor the hollow note is unbonded render. Do not let a quote for new render claim the survey found rotten brick, or sound brick, behind a coating that stayed on.
What should you ask your surveyor?
- How far did the hollow sound extend when you tapped?
- Did you open any of that patch, or only tap the coating?
- What, if anything, could you say about the brick behind it?
What are the typical next steps?
- Treat the hollow tap as unbonded render in that patch.
- Do not read it as a verdict on the brick behind.
- Open the coating only if you actually need the brick seen.
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 hollow patch is dry to the touch, is the brick proved dry?
No. A dry outer face does not show the brick behind loose render. The tap recorded a hollow patch. It did not measure moisture in the masonry, and it did not prove the brick is dry or wet. Anything further about the hollow render patch would be a different visit, not this note.
Does hollow render mean the whole elevation must come off?
Not from one patch. The survey called one patch hollow. That does not set the area to be hacked off, and it still says nothing firm about the brick behind the coating. The survey stops at the hollow render patch and does not add any further conclusion.