Getting Rid of Mould in a Rented Flat Bathroom for Good

The black speckles come back every few weeks: along the silicone by the bath, in the corner above the shower, around the window frame. You scrub, it fades, and a month later it is back, and you start to wonder whether you will lose part of your deposit over it. We fought mould in a rented flat bathroom for two winters before we worked out what actually kept it away.

Our bathroom is a windowless box of about 3.5 square metres with an extractor fan that sounded busy but moved almost no air. Here is what we tried, what it cost, and where the landlord's responsibility starts.

Why mould in a rented flat bathroom keeps coming back

Mould needs three things: moisture, a surface to grow on, and time. A bathroom gives it all three. A ten minute shower can release roughly half a litre of water into the air, and two people showering daily adds up to around 7 litres a week in one small room. If that moisture cannot leave quickly, it settles on the coldest surfaces, usually the outside wall, the ceiling corners, and the window.

Cleaning removes the visible growth but not the conditions. That is why bleach feels like it works and then fails. The fix is to make the room dry out within about 30 minutes of a shower, every time.

Step one, measure before you buy anything

We spent 12 pounds on a small digital hygrometer and left it on the bathroom shelf for a week. The numbers told us more than any article:

• Straight after a shower, humidity hit 95 percent.
• An hour later it was still at 80 percent with the door shut.
• By morning it had only fallen to 70 percent.

Mould growth gets going when surfaces stay above about 70 percent relative humidity for long periods. Our bathroom basically never dropped below that line. Once you have your own numbers, you know which of the fixes below matter.

It is also worth checking the hallway and bedroom at the same time. If those rooms sit at 65 percent or more too, the whole flat is holding moisture and the bathroom is just where it shows first. That points to ventilation and heating across the flat, not only a better bathroom fan.

The routine that actually worked for us

Squeegee and towel the walls

This sounds tiny and it made the biggest difference. A 6 pound shower squeegee takes 60 seconds to run down the tiles and glass. That removes water that would otherwise evaporate into the room. We then wipe the window sill and the ledge with an old towel that goes straight in the wash.

Leave the fan on longer

Most extractor fans are wired to the light and stop when you leave. We asked our landlord to fit an overrun timer so it keeps running for 15 to 20 minutes after the light goes off. It cost him around 60 pounds for the part and an electrician's visit.

Open the door, not the window

Once the walls are wiped, we prop the bathroom door open so the damp air spreads into the warmer hallway, where the overall humidity is lower. In a flat with a window, open it fully for 15 minutes rather than leaving it cracked all day, which just chills the walls.

Keep the room slightly warm

Cold surfaces attract condensation. A bathroom kept at 16 to 18 degrees Celsius grows far less mould than one at 12. Our guide to keeping a small flat warm through winter covers how we do that without the bill climbing.

Cleaning existing mould properly

For mould on tiles, grout and painted walls, we use a spray with sodium hypochlorite or a hydrogen peroxide based mould remover, about 3 to 5 pounds a bottle. Ventilate the room, wear gloves, spray, leave for 10 to 15 minutes and wipe. Never mix bleach based products with anything containing ammonia or acid.

Silicone sealant is different. Once mould grows into it, the black stays because it is under the surface. We removed the old bead with a 4 pound sealant removal tool, cleaned the joint, let it dry for 24 hours, and ran a new bead of anti-mould sanitary silicone. Total cost about 15 pounds and an hour. Ask your landlord first, since some prefer to arrange it.

Where we disagree with the usual advice

Almost every guide tells you to buy a dehumidifier. For a small bathroom, we think that is often the wrong first purchase. A compressor dehumidifier costs 120 to 200 pounds, draws around 150 to 250 watts, and is awkward to run safely in a wet room with limited sockets. It also treats the symptom while the extractor fan, which is the landlord's responsibility, stays broken.

A dehumidifier earns its place elsewhere in the flat, especially if you dry clothes indoors, which we wrote about in drying laundry indoors without the damp. In the bathroom, fix the airflow first, and only add a dehumidifier if the hygrometer still shows high readings after a fortnight.

We also skip the "anti-mould paint" quick fix. It helps on a sound wall but just hides the problem if the room stays wet, and painting a rented flat often needs permission anyway.

What your landlord has to fix

Tenants are expected to ventilate, heat reasonably and clean. Landlords are responsible for the structure and for things like extractor fans, leaks, broken seals on windows, and insulation problems. Under rules that came into force for social housing and have shaped expectations in private renting too, landlords are expected to investigate damp and mould promptly once told about it.

Our practical approach:

1. Photograph the mould with a date stamp and note the hygrometer readings.
2. Test the fan by holding a single sheet of toilet paper near it. If it does not cling, the fan is too weak.
3. Email the landlord or agent with the photos and readings so there is a written record.
4. Keep doing your part and note it, so nobody can blame lifestyle alone.

Our fan was replaced with a stronger model within three weeks. Since then the hygrometer drops below 65 percent within 40 minutes of a shower, and we have not seen new mould in eight months.

Frequently asked questions

Is mould in a rented bathroom the tenant's fault?

Not automatically. Condensation from daily life is normal, and if the fan, windows or insulation are inadequate, the landlord should fix them. Tenants are expected to ventilate and clean, so keep a record of what you do.

What kills black mould on bathroom silicone?

Surface cleaners lighten it but rarely remove it, because the mould grows into the sealant. Cutting out the old silicone and applying a new anti-mould bead is the only lasting fix. Let the joint dry fully before resealing.

How long should a bathroom extractor fan run after a shower?

Aim for 15 to 20 minutes after you finish. A fan with an overrun timer does this automatically. If humidity is still above 70 percent after that, the fan may be underpowered or blocked.