If you’ve got mould in the bathroom, you’re not alone. In a lot of Hertfordshire homes (especially the older ones, or the “sort of updated” ones), bathrooms are basically built to trap warm moisture. Then we act surprised when black spots show up on the ceiling or around the silicone.
And yes — you can wipe mould off. But if it keeps coming back, that’s your bathroom telling you the same thing over and over: the moisture isn’t leaving the room fast enough.
This is what actually causes bathroom mould, what’s worth doing yourself, and when it’s time to get someone in.
First: mould is a symptom, not the main problem
Mould needs three things:
- Moisture (steam/condensation)
- Something to feed on (dust, soap residue, paint, grout)
- Time (it keeps staying damp)
So the real question isn’t “how do I kill mould?” — it’s:
Why is this room staying wet for so long after a shower?
The most common causes (in real bathrooms, not perfect ones)
1) The extractor fan is too weak (or it’s not actually doing anything)
This is the big one.
A lot of bathrooms have a fan that technically turns on… but it’s either underpowered, badly ducted, clogged with fluff, or venting into the loft (which is a whole other problem).
Signs your fan isn’t coping:
- The mirror stays steamed up for ages
- The ceiling feels damp after showers
- You can smell “bathroom air” in the hallway
- Mould appears in the same corners again and again
Quick test: hold a single sheet of toilet paper up to the fan grille. If it won’t stick there while the fan’s running, it’s not pulling much air.
2) No “make-up air” (the fan can’t pull air if the room is sealed)
This catches people out.
If you’ve got a nice tight bathroom door, no gap underneath, and the window stays shut, the fan is trying to pull air out of a room that isn’t letting air in. It ends up doing very little.
What helps:
- A small gap under the door
- A vented door (in some setups)
- Cracking the window slightly during/after showers (even in winter — just for 10–15 minutes)
3) Cold surfaces + warm steam = condensation (especially on external walls)
Condensation is basically your shower steam turning back into water on the coldest parts of the room.
Common “cold spots”:
- External corners
- Around window reveals
- Ceiling above the shower
- Behind a big mirror on an outside wall
If the bathroom is cold, you’ll get more condensation. More condensation means more time damp. More time damp means mould.
4) Grout and silicone that’s past its best
Old silicone and porous grout love holding onto moisture and soap residue.
A few truths:
- If silicone is black all the way through, cleaning it is usually a losing battle.
- If grout is cracked or missing in places, water gets where it shouldn’t.
- If the seal around the bath/shower is failing, you can end up with damp behind the tiles — and then mould is the least of your worries.
5) “Looks fine” waterproofing behind the tiles (until it doesn’t)
This is the one people don’t want to think about.
Tiles and grout are not a waterproof barrier on their own. If the tanking/waterproofing behind a shower area wasn’t done properly, moisture can slowly work its way into boards and plaster.
Clues this might be happening:
- Paint bubbling or flaking near the shower
- A musty smell that won’t go away
- Tiles sounding hollow
- Grout that keeps cracking in the same line
If you suspect this, don’t just keep regrouting and hoping. Get it checked.
What to do (in the right order)
Step 1: Deal with the moisture, not just the mould
If you do nothing else, do these:
- Run the fan during showers and for 20–30 minutes after
- Crack the window for 10–15 minutes after bathing (yes, even when it’s cold)
- Keep the bathroom door closed while showering (so steam doesn’t spread through the house)
- Wipe down the worst condensation zones (window sill, tiles, mirror edges)
If you’ve got kids and you’re doing back-to-back baths, you’re basically running a steam room. You need ventilation that matches that reality.
Step 2: Clean it properly (without wrecking your bathroom)
Bleach is the classic go-to, but it’s not always the best answer — especially on porous surfaces.
Practical approach:
- Use a proper mould remover suitable for bathrooms
- Ventilate the room while you use it
- Don’t mix chemicals (ever)
- Rinse/wipe thoroughly, then dry the area
If mould is on painted ceilings, it often comes back unless the paint is mould-resistant and the moisture issue is fixed.
Step 3: Fix the “mould magnets”
These are the spots that keep feeding the problem:
- Replace silicone that’s stained through
- Repair cracked/missing grout
- Repaint ceilings with a bathroom-grade, mould-resistant paint (after cleaning and drying)
Step 4: Upgrade ventilation if it’s not up to the job
If your bathroom regularly steams up, the best “mould prevention” money you can spend is usually:
- A correctly sized extractor fan
- Proper ducting to the outside
- A timer/humidity sensor so it runs long enough
In a lot of homes, the fan is either too small, installed badly, or never runs long enough. Fixing that changes everything.
When to call a pro (because it’s not just surface mould)
Get someone in if:
- Mould returns within days of cleaning
- You’ve got staining that spreads or keeps appearing in new places
- There’s a persistent musty smell
- Paint is bubbling, plaster feels soft, or tiles are loose
- You suspect the shower area wasn’t waterproofed properly
If you’re in Harpenden, St Albans, Radlett, Welwyn Garden City, Borehamwood, Hemel Hempstead, Berkhamsted, or Leighton Buzzard, East & Gray can help you figure out whether it’s a ventilation issue, a sealing issue, or something deeper behind the tiles.
Quick FAQ
Does opening the window actually help?
Yes. Even 10–15 minutes makes a difference because you’re dumping humid air outside instead of letting it cool and condense on your ceiling.
Why does mould come back so fast?
Because the surface is staying damp. Cleaning kills what you can see; it doesn’t change the conditions that let it grow.
Is mould around silicone always a leak?
Not always. Often it’s just a damp, dirty edge that never fully dries. But if the seal is failing or water is getting behind tiles, it needs attention.
Should I use a dehumidifier?
It can help in some homes (especially if ventilation is limited), but it’s usually a “supporting tool” — not a replacement for proper extraction.