Mould, damp stains and efflorescence on walls in Geneva

Read the mark before treating it

A damp stain is not repainted, it is diagnosed. Each type of mark has a recognisable appearance, location and origin — and it is the origin that dictates the treatment, not the other way round. Repainting without understanding is a sure way to see the stain return.

Mark observed	Typical location	Likely cause	Painting-side treatment
Black or green film	Corners, behind furniture, ceiling	Condensation, thermal bridge	Antifungal sanitising, breathable finish
Sharp stain, brown outline	Anywhere, follows a leak	Leak, water damage	Cause first, drying, sealing coat
White powdery deposit	Base of wall, cellar, ground floor	Rising damp (efflorescence)	Brushing, neutralising, barrier
Diffuse stain that returns	Exposed wall, behind a cupboard	Chronic damp, overcrowding	Usage review, ventilation, finish

An examination under raking light and, where needed, a moisture reading of the surface make it possible to decide between condensation and a leak. This is the first step of a serious visit, before any quote.

Mould: almost always condensation

Black or green stains, slightly velvety, growing in corners, behind a wardrobe pushed against an external wall or on a bedroom ceiling, are the most frequent symptom. In the vast majority of cases, the cause is condensation, not a leak.

The mechanism is simple: the air in a home holds water vapour (showers, cooking, breathing, drying laundry). When that air meets a cold surface — a north-facing corner, a wall facing outside, a poorly insulated thermal bridge — the vapour settles as droplets. This chronic damp feeds mould. It is very common in older or poorly insulated Geneva buildings: pre-war blocks in Pâquis or La Jonction, badly ventilated flats, overcrowded rooms where the air does not renew.

On the painting side, the treatment follows a strict sequence: identifying the area, cleaning and antifungal sanitising of the surface, drying, preparation, then applying a finish suited to sensitive walls. But paint alone is never enough while condensation remains active: you also have to act on ventilation, heating and sometimes insulation — levers that go beyond the painter’s trade. The same reasoning applies to wet rooms, detailed in our guide to anti-damp bathroom painting.

Efflorescence: the signature of rising damp

Quite different is efflorescence, that white, powdery or crystalline deposit appearing at the base of a wall — typically in cellars, ground floors and the canton’s old stone walls. You wipe it off, it comes back. It is not mould but a salt deposit: mineral salts that groundwater carries as it rises through the wall by capillary action, crystallising at the surface as the water evaporates.

The height of the efflorescence fringe indicates the extent of the rising damp. Old walls without a damp-proof course, common in Geneva in the Old Town buildings or the basements of early twentieth-century blocks, are particularly exposed.

On the painting side, we brush the crystals off mechanically, neutralise with an anti-efflorescence product, and may apply a barrier coat before the finish. But let us be clear: as long as water keeps rising from the ground, the efflorescence will return. Lasting treatment of the rising damp — a damp-proof course, drainage, drying out the wall — belongs to a damp specialist, not the painter. Our role is to prepare the surface correctly and coordinate our work with that of the relevant trade.

Leaks and water damage: a different logic

A stain with a sharp outline, brown or yellowish, sometimes far from any corner, looks neither like condensation mould nor efflorescence. It follows a leak or water ingress: a roof, a facade exposed to the wind and driving rain, a pipe, a failing joint. As long as the source is running, repainting is pointless — the stain bleeds back through the finish.

The procedure is different: the leak must first be repaired, then the surface must dry all the way through, which is checked with a moisture meter and generally takes several days depending on the volume of water, the surface and the ventilation. A stain-blocking primer is then essential to prevent salts and tannins rising through the paint. When the origin is a declared claim, the insurance steps have their own logic: see our resource on water damage and the insurance steps and the water-damage repair service.

What paint solves — and what it does not

This is the most important point on this page, and the most honest. A sanitising, anti-damp or breathable paint has a real role: sanitising a mark, letting the wall breathe, delaying the return of mould, restoring a healthy appearance. It is a quality finish on a treated surface. It is not a treatment of the cause.

Paint can	Paint cannot
Sanitise and neutralise a mouldy area	Fix poor ventilation
Treat and block efflorescence at the surface	Stop rising damp at the source
Seal a dried-out leak stain	Repair a leak or waterproofing
Provide a breathable, washable film	Correct a thermal bridge or an insulation defect

Repaint without treating the cause and the damp returns — it is mechanical. Ventilation (VMC), waterproofing, drainage and insulation belong to other trades. Renovhome SA does not claim to carry them out: when the diagnosis shows it, we say so, and we coordinate our work with the relevant specialist so the finish lasts. To tell a simple finish problem from a real surface problem, see also flaking, blistering or chalking walls.

How Renovhome SA works in Geneva

During an on-site quote visit, a dedicated contact examines the nature of the mark, its location, the room’s exposure and the way the home is used, under raking light and, if necessary, with a moisture reading of the surface. The aim: to identify the cause honestly before proposing a treatment.

The method applied:

• Diagnosis: distinguishing condensation, a dried-out leak and rising damp; identifying the underlying causes.
• Sanitising: antifungal treatment of mould, brushing and neutralising of efflorescence.
• Consistent preparation: scraping, filling, primer or barrier coat depending on the case.
• Suitable finish: sanitising, breathable or stain-blocking paint, depending on the surface.
• Honest coordination: if the cause is beyond paint, referral to the right trade.

Painting work is covered by the 2-year legal warranty (Art. 371 CO). The paints used have low VOC emissions; a faint residual smell may linger briefly after the work. For a wall that is going mouldy or showing damp stains, request your free quote or get in touch with Renovhome SA — the on-site diagnosis is the first step, and the most useful one.