There is almost always water getting in somewhere, it just is not a burst pipe. Where the patch sits is the best clue to where it is coming from.
When there is no obvious leak, the usual causes are rain getting through the outside wall, condensation on a cold patch of wall, a hidden pipe in or behind the wall, or the ground, a path or a flower bed outside sitting higher than it should against the wall.
The position of the patch narrows it down: low above the skirting, in the middle of an outside wall, around a window, on a chimney breast or on an internal wall all point in different directions.
Often blamed on rising damp, but just as often a path, patio or flower bed built up against the outside wall, a leaking pipe in the floor, or condensation at the coldest part of the wall.
Rain getting through: cracked render, poor pointing, a blocked cavity, or a gutter or downpipe soaking the wall outside.
A failed seal round the frame, a sill without a drip, or condensation on a cold window reveal.
Rain in the stack or round the flashing, a capped flue with no ventilation, or salts left by years of burning fuel that draw moisture from the air in damp weather.
An internal wall has no outside face, so look for a pipe in or behind it, a shower or sink on the other side, or salts left by an old leak.
Corners are the coldest part of a room. Damp and black mould in a corner is very often condensation.
Go out after heavy rain if you can, and look at the wall directly behind the patch.
A damp patch on a chimney breast that appears in wet or humid weather and fades in dry spells is very often hygroscopic salts. Years of burning coal and wood leave salts in the brickwork and plaster, and those salts pull moisture out of the air. The patch can come and go with the weather even though no water is getting in.
A patch that grows after rain, especially high up near the ceiling, points instead to rain getting into the stack, the flashing or an uncapped pot. A capped chimney with no ventilation can also trap moisture inside the flue.
Maybe, but less often than you might be told. Rising damp affects ground floor walls only, sits low, and comes with a tide mark and salts. All of those can be caused by something else, and a moisture meter cannot tell the difference. Read can a damp meter prove rising damp? and before you pay for damp proofing.
Vigilant Surveys is an independent damp and mould surveying practice covering East Anglia, North London and the West Midlands. We carry out no remedial work, sell no products and take no commission from anyone who does the repairs, so there is nothing to sell you afterwards.
Every survey includes thermal imaging, moisture readings against a dry control and hygrometer readings, and you get a clear written report within 24 hours of the visit. £350 for the problem areas, £450 for the whole property, fixed prices, no payment to book.
An internal wall has no outside face, so rain is unlikely. Look for a pipe in or behind the wall, a shower, bath or sink on the other side, or salts left behind by an old leak that draw moisture from the air in damp weather.
Either rain is getting into the stack, flashing or pot, or salts from years of burning fuel are drawing moisture from the air. A patch that comes and goes with humid weather points to salts; one that grows after rain points to water getting in.
Not necessarily. A path or flower bed built up against the outside wall, a leaking pipe in the floor, or condensation at the coldest part of the wall can all cause damp low on a wall. Rule those out before paying for a damp proof course.
Because water is getting in from outside. Check the gutters, downpipes, render, pointing, window sills and ground levels on the outside of the wall directly behind the patch.
Only once the cause is fixed and the wall has dried out. Painting over a wall that is still wet traps the moisture, the paint blisters, and the patch comes back.
No payment to book. Tell me what you are seeing and I will call you straight back, usually within a couple of hours, to arrange a visit and confirm the fixed price.
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