Condition ratings
Mould sits on the bathroom silicone. Has the plaster behind the tiles been rated 3?
No. Mould on the bathroom silicone has not rated the plaster behind the tiles as 3. The mould is on the sealant bead that was visible. Plaster behind tiles is covered. Covered plaster was not inspected, so it has no rating 3 and no rating 1 either. Deal with the seal as the thing that was seen.
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?
Silicone is the flexible seal at the bath, the tray or the basin. Mould on it is a surface growth on that bead. It is common where the seal stays wet, and it is not a view of the plaster behind the tiles. The tiles were not taken off. The plaster behind them was not inspected, so the mark for that plaster is NI if it is mentioned at all, and NI is not rating 1 and not rating 3. The seal itself might be rating 2, a replacement that is needed but is not serious or urgent, or rating 1 if the surveyor thinks no repair is currently needed and the mould is only a clean. It becomes rating 3 only if they say the defect is serious or urgent.
Do not tell the seller the wall behind the tiles has failed. The what to do now note advises you. It does not invoice anyone to hack off a bathroom, and the quotation step belongs to rating 3, not to every black bead. Concealed plaster is not guaranteed sound, which is a limit, not a finding that it is rotten. A soft chipboard floor beside the bath, if the report has one, is a different element and was dealt with on its own terms. Ask whether the mould is only on the silicone. Replace the bead, once you own the room, if that is all that was described.
What should you ask your surveyor?
- Is the mould only on the silicone that you could see?
- Is the plaster behind the tiles NI?
- What rating, if any, did you give the sealant?
What are the typical next steps?
- Keep the mould on the silicone bead.
- Do not rate the hidden plaster as 3 or as 1.
- Do not ask for the tiles to come off unless the report says the defect is behind them.
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 black silicone be rating 2 with the tiles left at rating 1?
Yes, if the tiles need no repair now and the bead needs a replacement that is not urgent.
Does mould in the grout change the plaster?
Grout is still the face. Plaster behind the tiles stays uninspected until it is opened.