Sign of damp
Damp grout lines
Grout lines that stay dark long after the floor or wall has dried, turn black or green, crack, or are missing altogether. Tiles near them may sound hollow, have lifted edges, or show white salts in the joints. Most common in bathrooms, around floor traps and at kitchen splashbacks.
What it might mean in a flat
Dark, stained or missing grout in tiles.
In a bathroom, damp grout is often where the leak to the flat below begins. Water that gets past the tiles soaks into the bedding mortar and, if the waterproofing has failed, through the slab. In a new flat, missing grout and unsealed fittings are snag items that are cheapest to fix before possession and interiors.
Common causes
- Missing or cracked grout letting water past the tiles into the bedding and the slab
- Failed or missing waterproofing under the bathroom floor
- A floor slope that runs away from the floor trap, so water sits on the tiles
- Gaps around the floor trap, WC base, mixer and pipe entries left unsealed
- A leak from a concealed pipe behind wall tiles
What an inspection checks
How we confirm it.
- Pinless meter scans over tiled floors and walls to find wet areas behind the tiles, against a dry reference
- Thermal images of the floor and walls after normal use where possible, with cool areas confirmed by the meter
- Floor slope towards the trap, checked with water where the owner permits
- Condition of grout and sealant at the trap, WC, mixer and pipe entries
- Readings on the walls outside the bathroom and, where access is given, the ceiling of the flat below
When to worry
Signals that it's active.
- The wall outside the bathroom or the ceiling below reads wet
- Tiles sound hollow or rock underfoot
- Water pools away from the floor trap
Where it usually comes from
Questions buyers ask
Will re-grouting stop a bathroom leak?
It helps if the grout is the main way in and the waterproofing beneath is still sound. If the waterproofing has failed, the floor usually needs to be redone.
Can you see through tiles?
A pinless meter and a thermal camera can show a wet area behind tiles from the surface. They do not tell you exactly how deep the water is, and the report does not claim to.
Is this a snag item for a new flat?
Yes. Missing grout, unsealed fittings and the wrong floor slope go on the Possession Check list so the builder can fix them before you move in.
Not ready to book? Walk the flat with our 10-minute self-check and get a snag list to take to the seller.
Start the Damp CheckFind the damp before you pay for it.
Book a moisture and thermal inspection. Report on WhatsApp within 24 hours.