Not all damp is the same
The single biggest reason damp treatments fail is that the wrong type of damp is treated. There are three distinct mechanisms, each with a completely different cause and cure. Condensation is moisture from the indoor air landing on cold surfaces. Penetrating damp is water getting in from outside through a defect — a failed gutter, cracked render, a leak. Rising damp is groundwater drawn up through the wall. Diagnose the mechanism correctly and the fix is clear; get it wrong and you can spend thousands with no improvement.
In our experience across London, a large share of 'damp walls' turn out to be condensation — yet they are frequently treated as rising damp with chemical injections and tanking that were never going to work. A damp walls investigation establishes which mechanism you actually have.
Condensation: the most common cause
When warm, moist air meets a cold wall — especially a solid uninsulated wall, a corner, or a thermal bridge — it condenses, leaving the surface damp and prone to mould. This is often mistaken for rising or penetrating damp because the wall genuinely is wet. The tell-tale signs are damp that is worse in winter, on cold external walls, and accompanied by mould rather than tide marks or external defects.
Penetrating and rising damp
Penetrating damp follows a defect: a leaking gutter or downpipe, cracked or missing render, defective pointing, a roof leak, or a bridged cavity. It often appears as a localised patch that worsens after rain. Rising damp draws groundwater up through the base of a wall and typically shows as a tide mark low down, with salts in the plaster. Each needs a targeted repair — and each is quite different from condensation. Our investigation looks for the evidence that distinguishes them.
How Retrofit IQ investigates damp walls
We measure rather than assume. Surface and air moisture readings, relative humidity, temperature and dew-point analysis reveal whether condensation is occurring. Thermal imaging locates cold surfaces, thermal bridges and moisture patterns, and can help reveal water tracking from an external defect. We inspect the wall construction and, where relevant, external elements and ventilation. This lets us diagnose the true mechanism and design the correct remedy — rather than defaulting to a standard 'damp treatment'.
Part of a full Building Performance Investigation
Because most damp-wall problems in modern homes are linked to cold surfaces, insulation and ventilation, a damp walls investigation is often best carried out as part of a full Building Performance Investigation, which ties these factors together into one prioritised plan and protects the fix over the long term.
Salts, staining and reading the wall
A damp wall carries clues in its appearance, and reading them correctly is part of the diagnosis. A tide mark low on the wall with a band of salts can indicate rising damp; a localised stain that darkens after rain suggests penetrating damp from an external defect; diffuse damp on a cold surface with mould, worse in winter, points to condensation. Bubbling paint, blown plaster and efflorescent salts each tell a story about how moisture is moving. We combine these visual signs with instrument readings and thermal imaging, because appearance alone can mislead — but ignored, it misses valuable evidence.
Basements and below-ground damp
Damp in basements and below-ground rooms behaves differently, because the walls are in contact with the surrounding ground and subject to water pressure as well as condensation. A cold below-ground room can suffer heavily from condensation, while genuine water ingress needs a different, drainage-based solution. Diagnosing which is at work is essential before any lining, tanking or drainage is considered — applying the wrong system below ground is both expensive and, if it traps water, potentially damaging. Our investigation establishes the mechanism first.
Breathability and the wrong materials
Older solid-walled homes were built to handle moisture by letting it evaporate — they 'breathe'. Applying modern, impermeable materials such as cement renders, plastic paints or non-breathable tanking to these walls can trap moisture, causing damp to appear where it never did before and sometimes damaging the masonry. A common cause of stubborn damp in period homes is exactly this mismatch of materials. Part of our role is to recognise a breathable construction and steer you away from treatments that would do more harm than good.
What the report gives you to act on
You finish a damp walls investigation with an independent, evidence-based diagnosis rather than a sales pitch. The report identifies the mechanism, explains the evidence behind that conclusion, and sets out the correct remedy — whether that is warming surfaces and improving ventilation for condensation, repairing an external defect for penetrating damp, or a genuinely targeted approach where rising damp is present. Crucially, because we do not sell damp-proofing products, that recommendation is driven only by what your wall actually needs — the strongest protection against paying for the wrong cure.
What you receive
How we tell condensation from rising and penetrating damp
The three mechanisms leave different fingerprints, and reading them correctly is the core of the investigation. Condensation is usually worse in winter, appears on cold external walls, in corners and behind furniture, and comes with mould rather than staining. Penetrating damp tends to be localised, worsens after rain, and traces back to an external defect. Rising damp shows as a tide mark low on the wall, often with salt deposits in the plaster, and is far rarer than the treatment industry would suggest. We combine moisture readings, thermal imaging, dew-point analysis and inspection to establish which pattern fits — rather than assuming.
The trouble with 'free' damp surveys
Many damp surveys are carried out by firms that also sell the treatment, which creates an obvious conflict of interest: if the only tool you sell is a chemical damp-proof course, every problem starts to look like rising damp. This is one reason so many homeowners pay for injections, tanking and replastering that never solve the problem — because the problem was condensation all along. Our investigation is independent and diagnostic. We do not sell damp-proofing products; we tell you what is actually happening and what genuinely needs doing.
External defects that cause penetrating damp
When the diagnosis is penetrating damp, the cure is to fix the defect letting water in — not to treat the inside face. Common culprits include blocked or leaking gutters and downpipes, cracked or missing render, defective pointing, failed window seals, raised external ground levels bridging the damp-proof course, and roof or flashing leaks. Part of our investigation is looking for these external causes and linking them to the internal symptom, so the repair addresses the source. Treating the wall internally while water keeps entering from outside is a recipe for the problem returning.
Protecting the repair for the long term
A lasting fix depends on matching the remedy to the mechanism and then keeping the conditions right. For condensation, that means warmer surfaces, moisture control and ventilation working together; for penetrating damp, a durable external repair; for rising damp, a properly targeted approach where genuinely present. Our report sets out not only what to do now but how to keep the wall healthy afterwards — because the aim is to solve the problem once, not to manage it forever. This is where a measured, independent diagnosis pays for itself many times over.
- A clear diagnosis of the true damp mechanism
- Moisture, humidity and dew-point findings
- Thermal images of cold surfaces and moisture patterns
- An assessment of construction and, where relevant, external defects
- A targeted, prioritised remedial strategy
A real-world investigation example
A homeowner was quoted for a chemical damp-proof course and full replastering after a 'free' damp survey diagnosed rising damp in a hallway. Before committing, they asked for an independent investigation. Moisture profiling, thermal imaging and dew-point analysis showed no genuine rising-damp signature: the damp was diffuse, worst in winter, sat on a cold solid wall and came with mould — the fingerprint of condensation. There was also a minor external defect, a cracked section of render channelling rainwater to one patch. The correct remedy — repairing the render, warming the surface and improving ventilation — cost a fraction of the damp-proofing and actually solved it.
Common homeowner mistakes
The biggest mistake is accepting a diagnosis of rising damp from a firm that also sells the treatment, then paying for injections and tanking that a condensation problem never needed. Another is replastering over a damp wall, which hides the symptom until it inevitably returns. Applying modern, non-breathable cement renders or plastic paints to an older breathable wall traps moisture and creates new damp. And treating the inside face while an external defect keeps letting water in guarantees the problem comes back.