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Daily use puts the bathroom under constant strain. When you take a hot shower, the moisture this creates attacks the walls of the room and, if the room is not ventilated enough, can lead to harmful mould growth. Mould thrives in warm, humid conditions and spreads not only on the walls but also in the tile joints and on silicone seals. Tile joints protect the gaps between tiles from water penetration and are naturally under the most strain in the bathroom. Over time, silicone becomes brittle and cracked, creating a breeding ground for mould. Once mould appears in the bathroom, it can quickly become a lasting problem.
You can recognise mould by its black discolouration. If you see it, you should replace the joints. If you are handy, you can do this yourself. Small spots of mould can be removed yourself with a few simple tricks. If the joints have only turned yellow, there is no need to replace them or use a mould cleaner. Yellowed joints can easily be cleaned with a tried-and-tested home remedy.
You can clean yellowed or dirty joints with baking soda and water for less than CHF 5 and about an hour of soaking time. If the joints are black, however, it is usually mould: cleaning is then not enough, and you need to kill the mould (see next section).
This is how it works:
While cleaning check whether cracks have already formed in the joint. If black mould is also growing in it, you should think about replacing the putty joints. Below we explain how you can replace the joints yourself with a little manual skill.
You can remove small mould spots in joints (smaller than the palm of your hand) yourself with 70–80% alcohol. For larger or recurring mould, call in a professional: a mould survey alone costs CHF 250 to 1,000.
If you have discovered black stains, you should act - because mold is harmful to health and destroys the fabric of the building. You can treat small stains yourself before you replace the putty joints or call in a professional.
This is how it works:
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You can remove mould from tile joints (cement grout between the tiles) with 3% hydrogen peroxide or a chlorine-based mould remover for CHF 5 to 20. If the mould has penetrated deep into the joint, have the tile joints raked out and regrouted: a tiler charges around CHF 40 to 80 per square metre.
Unlike silicone joints, tile joints are porous. Mould therefore grows into the joint and cannot simply be wiped off. Here is how to get mould out of tile joints:
Important: vinegar and vinegar-based cleaners attack cement grout and make it even more porous, so they are not suitable for tile joints.
If the mould in the shower joints is light, remove it with alcohol or a mould remover for CHF 5 to 20. If the silicone joint is black all the way through, replace it: doing it yourself costs around CHF 20 to 40.
Humidity is highest in the shower, which is why the joints there go mouldy first. Black dots in the silicone joint show that the mould has already grown into the material. Cleaning products will at most bleach the stains, and the mould comes back within a few weeks. Typical signs that you should replace the shower joint:
After showering, it helps to dry the joints with a squeegee or cloth and air the bathroom thoroughly for 5 to 10 minutes.
70–80% alcohol, 3% hydrogen peroxide and chlorine-based mould removers are effective against mould in joints. They cost between CHF 5 and 20 per bottle. Home remedies such as baking soda or vinegar only remove discolouration and do not reliably kill mould.
Never mix chlorine-based products with other cleaners, and only use them with the window open.
You can remove mould on bathroom walls or ceilings yourself as long as the area is smaller than the palm of your hand: with alcohol or a mould remover for CHF 5 to 20. If the area is larger or the mould comes back, you need a specialist company. Professional mould removal costs from CHF 1,000.
Black mould in the bathroom is almost always caused by excessive humidity: above about 70 per cent relative humidity, mould spores multiply unchecked. Proceed as follows:
Read more in our article “Mould: prevention is better than removal or remediation”
You can replace a mouldy silicone joint yourself for around CHF 20 to 40 in materials (silicone, caulking gun, silicone remover, joint smoothing tool) and 24 hours of drying time. If you have the bathroom joints repaired, expect to pay CHF 10 to 20 per linear metre plus call-out charges.
This is how it works:
For bathrooms and showers, use a sanitary silicone with a fungicidal (anti-mould) finish. It costs hardly more than standard silicone and delays new mould growth.
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Apply 70–80% alcohol or 3% hydrogen peroxide, leave it to work briefly and wipe the joint dry. If the mould comes back, it is inside the material: you then need to replace the joint.
Baking soda removes discolouration on yellowed joints for under CHF 5. However, it does not reliably kill mould. Alcohol from a chemist or pharmacy is more effective. Vinegar is not suitable for cement grout because it attacks it.
Yes, mould spores can irritate the airways and mucous membranes and trigger allergies. Remove small spots immediately and have larger infestations assessed by a specialist.
Treat small spots with alcohol straight away, replace mouldy silicone joints and tackle the cause: air the room thoroughly after every shower. For areas larger than the palm of your hand or recurring mould, call in a mould specialist.
Black joints are usually mould, not dirt. Treat them with hydrogen peroxide or a mould remover. If the joint stays dark, the only solution is to rake it out and regrout.
Expect to pay CHF 10 to 20 per linear metre for silicone joints and CHF 40 to 80 per square metre for regrouted tile joints. There is often an additional call-out fee or minimum charge.
