Cause first, then product
Mould grows where surfaces stay damp for extended periods. The cause is either water entering from outside or from pipes, or humidity condensing on cold spots such as corners of exterior walls, window reveals or behind furniture. A disinfectant removes the visible growth but does nothing about this cause. If the cause is not fixed, mould usually returns within weeks.
- Could there be water damage, a leak or a failed seal?
- Does the mould appear on cold exterior walls, in corners or behind cupboards?
- How do you ventilate and heat, and how high is humidity in winter?
- Was there a recent renovation, for example new, more airtight windows?
Rented flats
As a tenant you are obliged to report defects such as mould to the landlord. Do so in writing and with photos before taking major measures. Who is responsible for the cause is often only clarified by an expert assessment.
When you can act yourself
Small, superficial growth on smooth or low-absorbency surfaces can usually be removed yourself. Many guidance sheets cite an area of around half a square metre as the limit for DIY treatment, provided the cause is known and fixed. Larger, recurring or hidden growth should be handled by a professional.
- Do not brush the growth off dry or use an ordinary vacuum cleaner, as this releases spores into the air.
- Apply the product with a disposable cloth or sponge and observe the contact time.
- Wipe off the growth with fresh cloths and dispose of them immediately in a sealed bag.
- Treat the surface a second time and let it dry thoroughly.
- Watch the spot over the following weeks: if the growth returns, the cause has not been fixed.
Protect yourself
Wear gloves, safety glasses and an FFP2 or FFP3 respirator. Ventilate well, close doors to other rooms and dispose of cloths immediately with household waste. People with asthma, allergies or weakened immune systems, as well as pregnant women and children, should not do this work themselves.
Which products suit which purpose
| Product | Suitable for | Note |
|---|---|---|
| Ethanol or isopropanol, around 70 to 80 percent | Small areas, including plaster and wood | Evaporates without residue; flammable, keep away from open flames |
| Hydrogen peroxide solutions | Smooth and mineral surfaces | May bleach; follow the concentration on the label |
| Chlorine-based cleaners | Only non-absorbent surfaces such as tiles | Never mix with acidic cleaners, as toxic gases form; bleaches, barely works in pores |
| Professional products, some for room fogging | Large-scale growth, cavities, after water damage | Applied by specialist firms with protective equipment |
Vinegar is often recommended but is of limited use: it does not reliably work against all mould species and can attack lime-based surfaces. Ordinary household cleaners remove discolouration but do not reliably kill spores. For disinfectants, look for a valid Swiss authorisation as a biocidal product and follow the contact time and dosage on the label.
Limits of disinfection
If mould has grown through porous materials such as wallpaper, plasterboard, insulation or silicone joints, treating the surface is usually not enough. These materials generally have to be replaced. Dead spores can still trigger allergic reactions, so the growth should be removed thoroughly after disinfection.
Do not paint over it: anti-mould paint only goes on the wall once the cause is fixed and the growth removed. Otherwise the problem is merely hidden.
When a professional is needed
- The growth is larger than about half a square metre or appears in several places.
- The mould returns after treatment.
- There is a musty smell without visible mould, which may indicate growth in cavities.
- There has been water damage in floors, walls or ceilings.
- Occupants report health complaints.
Specialist mould remediation firms measure moisture, identify the cause, remove contaminated components and use room disinfection where needed. After water damage, it is worth notifying the building insurance or contents insurance early, depending on cover.