Salt damp in coastal homes comes from hygroscopic salts, mainly chlorides from sea spray and salt-laden air, that pull moisture from the atmosphere and can push a moisture meter reading up even without any active water source. It tends to sit on exposed, sea-facing elevations and stays fairly stable over time. A leak, by contrast, is usually localised, worsening, and linked to pipework. Both can occur in the same property, so a pattern that doesn't fit typical salt damp is worth checking properly.
Properties near the Cornwall and Devon coast deal with a kind of damp that inland homes rarely encounter: salt worked into the fabric of the building itself, drawing moisture from the air on an otherwise dry day. That makes reading a damp patch, or a moisture meter, more complicated than it is inland, because salt damp in coastal homes can look remarkably similar to the early stages of a hidden leak. This guide sets out how the two differ, and when a coastal damp pattern is worth investigating as a possible leak rather than accepting as normal sea-air weathering.
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What salt damp actually is
Salt damp is caused by hygroscopic salts, mostly chlorides, that accumulate in masonry, render and plaster near the coast over years of exposure. "Hygroscopic" means the salt itself actively attracts and holds water from the surrounding air, rather than simply being present because water once passed through. That's the key difference from most other forms of damp: the salt doesn't need an active water source to keep a wall reading wet, it just needs humid air, which the Cornish and Devon coast supplies in generous quantities most of the year.
Over time, salt-affected walls can show a pattern of blown or crumbling plaster, a persistent tide-mark-like staining, or a fine white powdery deposit on the surface as the salts crystallise and dissolve with changing humidity. None of that, on its own, points to a leak. It points to years of coastal exposure doing exactly what coastal exposure does to a building's fabric.
Why salt skews a moisture meter reading
A standard pin-type moisture meter measures electrical resistance between two pins and converts that into a wood-moisture-equivalent reading. Salt water conducts electricity considerably better than plain water, so a wall carrying dissolved chlorides will show a higher reading than its actual water content would justify on a clean, salt-free wall.
This matters enormously for coastal homes, because the standard damp meter bands used across the industry, roughly below 17 as dry, 17 to 20 as borderline, and above 20 as wet on the common %WME pin scale, were established without accounting for salt contamination. A coastal wall can sit in the "wet, action needed" band on a meter and simply be a normal, dry-to-the-touch, salt-laden wall doing what it always does in damp weather.
| Reading behaviour | Typical cause | What it means here |
|---|---|---|
| Consistently elevated across a whole sea-facing wall, stable over months | Salt contamination in the masonry | Likely background salt damp, not an active leak |
| Elevated in one localised patch, near pipework or above a wet room | Possible plumbing leak | Worth investigating regardless of surrounding salt levels |
| Reading rising over weeks in the same spot, getting worse | An active, ongoing water source | Points away from stable salt damp toward a leak |
Sea-spray penetration versus airborne humidity
There are really two separate coastal mechanisms at work, and they behave differently.
- Wind-driven sea spray physically carries salt-laden moisture onto exposed render, stone and pointing during storms and onshore gales, concentrated on the windward, sea-facing elevation of a property. This deposits fresh salt and moisture directly onto and into the surface.
- Airborne humidity, the everyday damp coastal air found across most of Cornwall and Devon's coastline, continues to interact with salts already absorbed into the wall from years of past spray exposure, drawing moisture in on humid days even when there's no active spray event happening.
The practical upshot is that exposed, sea-facing elevations carry more salt and read damper more consistently than sheltered elevations of the same building, and that difference is a useful diagnostic in itself: a leak doesn't usually respect which side of the house faces the sea, but salt contamination does.
Telling salt damp apart from a leak
The pattern, more than the number, is what separates the two:
- Salt damp is typically widespread across an exposed elevation, fairly stable from month to month, and often shows a visible white, powdery salt deposit or blown plaster.
- A leak is typically localised to one patch, tends to worsen over time rather than stay level, and sits near pipework, a bathroom above, or a kitchen or utility run.
- A leak is also more likely to come with a secondary sign a salt pattern won't produce: an unexplained rise in the water bill, a sound of running water with everything off, or warmth in a patch fed by a heating pipe.
Our broader guide to condensation or a leak covers the equivalent distinction for inland properties, and the same logic of pattern-over-number applies here, with salt contamination as an extra variable specific to the coast. If you've already ruled out condensation and are still looking at an unexplained damp patch on the wall, salt contamination and a leak are the two remaining explanations worth weighing against each other.
Granite and cob: older coastal construction
Traditional Cornish and Devon construction adds another layer to this. Granite, a common building stone across Cornwall, and cob, a dense earth-based wall material found in older Devon and Cornish cottages, are both more porous and absorbent than modern cavity brick or blockwork. That means they take up more salt and moisture from coastal exposure over the decades, and hold onto it for longer once absorbed.
This doesn't make these properties unsound. It means a moisture reading in a granite or cob coastal cottage needs more careful interpretation than the equivalent reading in a modern house nearby, because the baseline "normal" for that wall is genuinely higher. We see this often in older coastal cottages: an owner alarmed by a reading that would be a concern inland, when for that specific wall, on that specific coastline, it's simply the material behaving as it always has.
When known salt contamination still needs a check
Knowing a property has salt-affected walls is useful background, not a reason to stop investigating every damp patch. The two situations that still warrant a proper check, even with known salt contamination in the building:
- A patch that's clearly localised rather than spread across the exposed elevation, especially if it sits near a bathroom, kitchen or pipe run.
- A reading or patch that's demonstrably getting worse over successive checks, rather than holding steady with the seasons.
In either case, non-invasive thermal imaging leak detection and calibrated moisture readings taken at multiple points, compared against known salt-affected and unaffected areas of the same building, separate a stable coastal pattern from an active water source without opening up walls on a guess. Where pipework is confirmed as the likely cause, the same visit typically moves into full water leak detection to pinpoint the exact source.
Frequently asked questions
What is salt damp and why does it affect coastal homes?
Salt damp is caused by hygroscopic salts, commonly chlorides carried in sea spray and salt-laden air, that work into masonry and plaster over time. These salts actively draw moisture from the surrounding air, so a wall can feel and read damp even without any water actively entering the building, simply because the salt keeps pulling humidity in.
Can salt in the walls give a false damp meter reading?
Yes. Pin-type moisture meters read a wood-moisture-equivalent value on masonry rather than a true percentage, and dissolved salts conduct electricity more readily than plain water, which pushes the reading higher than the wall's actual moisture content. A high reading on a salt-contaminated coastal wall does not automatically mean a leak.
How do I tell salt damp apart from a plumbing leak?
Salt damp tends to be widespread on exposed, sea-facing elevations, fairly stable over time, and often shows white, powdery salt deposits on the surface. A plumbing leak is usually localised, worsening, and sits near pipework, a bathroom above, or a kitchen run, frequently alongside an unexplained rise in the water bill.
Does sea spray actually get into the walls, or is it just the air?
Both happen. Wind-driven sea spray physically deposits salt-laden moisture directly onto exposed render, stone and pointing, especially on the windward, sea-facing side of a property, while salts already absorbed into the masonry continue to draw humidity from ordinary damp coastal air long after any spray event has passed.
Are granite and cob coastal homes more prone to this than modern houses?
Traditional granite and cob construction is more porous and absorbent than modern cavity-wall brick, so it tends to take on more salt and moisture over time from coastal exposure. That doesn't mean these properties are unsound, but it does mean a moisture reading needs more careful interpretation than the same reading in a modern house.
Should I still get a leak checked if I know we have salt contamination?
Yes, if the damp pattern is localised, getting worse, or near pipework rather than spread across an exposed elevation. Known salt contamination explains a general background reading, but it can also mask the early stages of a genuine leak, so a pattern that doesn't fit typical salt damp is still worth investigating properly.
How is a hidden leak confirmed in a coastal home with known salt damp?
Non-invasive methods such as thermal imaging and calibrated moisture readings taken across several points, compared against known salt-affected and unaffected areas, help separate a stable salt pattern from an active water source. Acoustic sensors and tracer gas then locate the leak itself if pipework is confirmed as the cause.
Not sure if it's sea air or a hidden leak
We survey coastal properties across Cornwall & Devon and can tell salt-affected background damp apart from an active leak, using non-invasive thermal imaging and moisture readings, with a clear report for your insurer if needed.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)