Sign of damp
Tide marks on skirting
A brown, yellow or grey band with a wavy upper edge running along the bottom of a wall, often just above the skirting tile. Below the line the paint may be darker, flaking or salted. The line can rise and fall with the seasons.
What it might mean in a flat
Wavy stain lines low on the wall.
The tide mark is the height where water rising or spreading through the wall evaporates and leaves salts behind. On a ground floor it often points to rising damp. On an upper floor rising damp is unlikely, so the usual suspects are the bathroom, kitchen or balcony next to that wall, or a pipe in the floor.
Common causes
- Rising damp in ground-floor flats and independent houses where the damp-proof course is missing, damaged or bridged
- A leaking floor trap, waste pipe or concealed supply line in the bathroom or kitchen next door
- Water seeping under the flooring from a balcony or utility area with the wrong slope
- Floor washing water soaking into the base of plaster that runs down behind the skirting
- Garden soil, planters or paving outside built up against the external wall
What an inspection checks
How we confirm it.
- Meter readings at several heights from the floor up, to see whether moisture falls off with height as rising damp usually does, or peaks near a pipe or trap
- Pinless readings alongside pin readings, because salt-loaded skirting plaster can give high pin readings even when dry
- Thermal scan along the base of the wall and the floor next to it to trace a wet band back towards a bathroom, kitchen or balcony, confirmed with the meter
- Floor level and slope at bathroom and balcony thresholds, and the condition of the grout and floor trap
- On ground floors, the outside ground level and anything built against the wall
When to worry
Signals that it's active.
- Readings are high across the full length of a ground-floor wall
- The band is higher on the side next to a bathroom, kitchen or balcony and readings rise towards it
- Skirting tiles sound hollow or have come loose, or wooden furniture against the wall is swelling
Where it usually comes from
Questions buyers ask
Can rising damp happen on the fifth floor?
Not from the ground. A tide mark on an upper floor usually comes from water spreading sideways or downwards: a bathroom floor, a kitchen pipe, a balcony with the wrong slope, or the floor above.
Why is the stain line wavy?
It marks where water spreading through the wall evaporates. That height changes with the wall, the salts and the season, so the line is rarely straight.
Will replacing the skirting tiles fix it?
Not if water is still reaching the wall. New skirting can hide the line for a while, but the source needs to be found and fixed first.
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