Killing mould solves nothing for as long as the damp stays. That is why the black patch is back after two weeks in exactly the same spot, however hard you scrubbed. Mould in the bathroom is not a cleaning problem but a damp problem.
Short answer
Take the mould away, and then take the cause away. Otherwise you will be doing it all over again in three weeks.
On tiles and sealant you can handle it yourself. If it is in the wall or it keeps coming back, the cause is structural.
Why mould grows in the bathroom of all places
Three things have to come together, and in a bathroom there are usually three.
Mould spores are in the air everywhere, all the time. They do nothing until they find a spot where they can grow, and this is what that takes:
- Damp, and above all damp that sits there. A bathroom that stays wet for two hours after a shower is a breeding ground.
- A cold surface. Warm, humid air condenses on the coldest plane in the room. That is usually the ceiling, the outside wall or the corner where two walls meet.
- Something to live on. Soap residue, skin oils, dust, and on a wall the glue in the wallpaper or the paint itself.
That is why mould is almost never in the middle of a tile and almost always in a corner, along the sealant or on the ceiling. Those are the coldest and the wettest spots.
And that is why cleaning only works for a while. You take the growth away and leave all three conditions standing.
Removing mould from the bathroom, step by step
This is how you tackle mould removal on tiles, sealant, ceilings and painted walls.
- Open a window or switch the extractor on first. Removing mould sets spores loose. Wear gloves, and for a larger area a face mask as well.
- Clean the surface first, do not go straight for the kill. Soap residue and grease form the layer the mould sits in. Take that off with a damp cloth and a little washing-up liquid, otherwise whatever you do next only works on that layer.
- Then deal with the mould itself. On a smooth surface heat is the most effective, because heat gets into the pore and leaves nothing behind that later becomes food again. Works with steam, or with a cloth and water as hot as you can get it.
- Dry it off and keep it dry. This is the step that decides whether it comes back. See the section on prevention further down.
Mould in the grout needs its own approach, because grout is porous cement. What keeps it away is getting the shower dry after every use, and that routine is in how to keep the shower limescale-free.
Mould on the bathroom ceiling
The ceiling is almost always the coldest plane, and so the first place it shows.
Warm shower air rises and condenses on the ceiling. If it sits there, that is where the growth starts first. So seeing it there and nowhere else is no coincidence.
Working above your head calls for two extra things. Protect your eyes, because everything you loosen falls down. And work in small sections, because a dripping ceiling leaves streaks down the wall.
If the ceiling is painted and the mould is only on the paint, you can usually get it off. If the paint is flaking, or the ceiling feels soft, it is in there and not on there. Then the layer has to come off, it has to dry out, and only after that can you repaint with a paint that stands up to damp.
If it comes back after painting, you do not have a paint problem but a ventilation problem.
Removing black mould: colour gone is not the same as mould gone
The most common misunderstanding on this subject.
For removing black mould most people reach for chlorine bleach, and that turns the patch white fast. What happens is that the pigment gets bleached. On a smooth surface such as a tile you take the mould itself with it, because there it sits on top.
On a porous surface it is a different story. In sealant, in grout, in plaster and in wood the mould is inside the material. You bleach the top white while the rest stays put, and then it looks solved when it is not.
That is how you can tell which of the two you have: if the black patch is back within a few weeks in exactly the same spot, it was in the material and not on it.
Once the sealant has gone black right through the rubber, replacing it is the only fix that lasts. You can kill the mould and the sealant stays black.
Mould on the wall: this is where cleaning stops
The honest limit, and it is what makes the rest credible.
A patch on a wall that keeps coming back is a signal, not dirt. There are four causes you can spot yourself:
- A leak. Often a pipe inside the wall or failed sealant behind the bath. The area is usually round and feels colder than the rest.
- Rising damp. Starts at the bottom and works upwards, often with a salt line.
- A cold bridge. A spot where the wall is less well insulated, at a concrete lintel for example, or in a corner. The mould then follows a straight line or sits exactly in the corner.
- Too little ventilation. Spread across the whole room instead of in one place, and worst behind cupboards and in corners.
Only that last one is yours to fix. With the first three you can scrub all you like: as long as the damp keeps coming, the mould comes back. That is no reason to despair, it is a reason to look for the cause before you buy another product.
If the mould is behind the wallpaper, the wall feels soft, or the plaster is crumbling, this is work for someone who can establish the cause. When you call someone in, always ask for a damp reading first, because without a cause every treatment is temporary.
The products measured up
Five things that get recommended, and what they do.
Chlorine or bleach
Works well on smooth material such as tiles and glass. On porous material it mostly takes the colour away. And it does not get on with acid: never mix it with vinegar or a limescale remover, because that releases chlorine gas.
Vinegar
Often recommended and not the best choice here. Vinegar deals with limescale, and you are putting moisture onto a spot where moisture is the problem. On lime-based grout it attacks the material as well.
Methylated spirits or alcohol
Evaporates fast and so leaves little moisture behind, and that is exactly why it tends to work out better on a wall than vinegar. Make sure there is ventilation and do not work near a naked flame.
Shop-bought mould spray
Does what it says, and it is usually chlorine bleach in a spray bottle. Usable on tiles and sealant, and it does not solve the damp problem. Do not leave it to dry in a room where you then spend two hours cleaning.
Steam
The strongest thing on a surface, because heat gets into the pore and no product is left behind to become food again later. On a wall it is not a solution for the cause, but it is for what you can see.
How to stop it coming back
This is the only part that really solves the problem.
Mould needs damp. A bathroom that is dry within half an hour of a shower does not get mould. That is the whole of prevention, and it costs you half a minute a day.
- Ventilate during and after your shower, and let the extractor run on for another half hour. Close the door while you ventilate, otherwise the humid air is pulled into the rest of the house.
- Give the wall and the shower screen a quick wipe with a dry cloth. That takes most of the water off in one movement.
- Do not let the bathroom go cold. A cold room lets moisture condense. A few degrees warmer makes more difference than you would think.
- Keep corners clear. A cupboard against an outside wall is the classic place where it starts, because no air gets there.
Is the mechanical extractor still working? Hold a sheet of kitchen roll against the grille. If it stays put, it is pulling. If it falls, the grille is blocked or the motor has stopped, and that is often the real cause.
Our cloths are at cleaning cloths. The same rule applies to the shower screen as to windows: see how to clean windows without streaks.
When you do not do it yourself
Two situations where you call someone in.
When the cause is structural. A leak, rising damp or a cold bridge is not something a product fixes. Every treatment is temporary then, and you pay twice.
When someone in the house has a respiratory condition. With asthma, an allergy or a weakened immune system it is wiser to leave the removal to someone else, because taking it away is exactly what releases spores.
When you get a quote, always ask what is being done about the cause and not just about the patch. A treatment without a damp reading is a clean with an invoice attached.
Frequently asked questions
What kills mould for good?
Nothing, for as long as the damp stays. You can take the growth away with heat or with chlorine bleach, but the spores are always in the air and they come back as soon as there is a wet, cold spot again. For good only exists if you take the cause away.
How do you remove mould from the bathroom?
Ventilate first and put gloves on. Clean the surface with a damp cloth and a little washing-up liquid, because the soap layer is what the mould sits in. Then deal with the mould itself, on smooth material best with heat. Dry it off and keep it dry.
How do I get mould off the ceiling?
Work in small sections and protect your eyes, because everything falls down. If the mould is only on the paint, it usually comes off. If the paint is flaking or the ceiling feels soft, it is in there: the layer has to come off and it has to dry out first.
Why does mould keep coming back?
Because the cause is still there. Mould needs damp, a cold surface and something to live on. If you only take the growth away, those three conditions are still standing. If it is back within a few weeks in the same spot, look at leaks, ventilation or insulation.
Does vinegar help against mould?
Only moderately, and in the wrong place it even backfires. Vinegar deals with limescale, and you are putting moisture onto a spot where moisture is the problem. On lime-based grout it attacks the material as well. Methylated spirits evaporates faster and is therefore often the better choice on a wall.
Does chlorine bleach work on black mould?
On tiles and glass yes, because there the mould sits on top. On porous material such as sealant, grout or plaster it mostly bleaches the colour while the rest stays put. Never mix chlorine bleach with vinegar or a limescale remover, because that releases chlorine gas.
How do I tell whether the damp problem is structural?
From the pattern. A round, cold area points to a leak. Starting at the bottom with a salt line points to rising damp. A straight line or exactly a corner points to a cold bridge. Spread across the whole room points to too little ventilation, and that is the only one you fix yourself.
Can I paint over mould?
That only works if the surface underneath is dry and free of mould. Paint over living mould lets go in time and the patch comes through it. Remove it first, let it dry, and only then paint with a paint that can handle damp.
Does a steam cleaner work on mould?
On a surface it is the strongest thing there is: heat gets into the pore and no product is left behind to become food again later. It does not solve a damp problem in the wall, but it does solve what you can see.
How do I prevent mould in the bathroom?
By getting the room dry quickly. Ventilate during and after your shower and let the extractor run on for half an hour, with the door closed. Give the wall a quick wipe with a dry cloth and do not let the bathroom get too cold.
How do I know whether my ventilation still works?
Hold a sheet of kitchen roll against the grille. If it stays put, the ventilation is pulling. If it falls, the grille is blocked or the motor has stopped. That is the cause more often than people think.
When do I call someone in?
When the cause is structural, so with a leak, rising damp or a cold bridge. And when someone in the house has a respiratory condition, because taking it away releases spores. Always ask for a damp reading: a treatment without a cause is temporary.
Elsewhere in the house
Mould in textiles works differently and is covered in removing mould from clothes. Everything sorted by job is under cleaning.