Bathrooms are a perfect storm for damp problems — constant humidity, frequent water splashes, and poor airflow create an environment where moisture loves to settle in.
Leave it alone, and damp becomes more than an eyesore; it can cause mould growth, structural damage, and even health risks.
I’ve seen it happen in my own home — one small patch of mould under the window turned into peeling paint, stained tiles, and an unpleasant smell that no candle could hide.
1. Understand What Damp Really Is Before You Try to Fix It
Before you grab a sponge and start scrubbing, you need to identify the type of damp you’re dealing with. Not all damp is created equal.
There are three main types you might find in a bathroom:
- Condensation damp – The most common. It happens when warm, moist air hits cold surfaces like mirrors, tiles, or windows, leaving water droplets behind. Over time, this moisture can lead to mould.
- Penetrating damp – Caused by water coming in from outside, often through cracks, damaged grout, or leaking pipes.
- Rising damp – Less common in bathrooms but still possible. This happens when moisture from the ground rises through walls because of a damaged or missing damp-proof course.
Why this matters:
If you treat condensation like penetrating damp, you’ll waste time and money. The cure depends on the cause. For example, a dehumidifier won’t solve a leaking pipe, and new grout won’t fix condensation.
Quick tip: A cheap digital hygrometer (around $10–$15) will tell you your bathroom’s humidity level. Anything consistently above 60% relative humidity is a breeding ground for damp and mould.
2. Spot the Early Signs Before They Get Worse
The tricky thing about damp is that it starts quietly and escalates fast. You want to catch it early, before it starts eating away at your walls or health.
Common early warning signs include:
- Black mould spots on walls, ceilings, or around grout lines.
- Peeling paint or wallpaper in patches.
- A musty smell that lingers even after cleaning.
- Condensation on mirrors and windows that doesn’t clear quickly.
- Discoloured or damp patches on ceilings (especially if there’s a bathroom above yours).
I remember visiting a friend whose bathroom had a faint earthy smell. They thought it was just poor ventilation. A month later, the smell was stronger, and we found a large black mould colony behind the sink cabinet. Lesson learned: Don’t ignore even small signs.
3. Improve Ventilation — Your First Line of Defence
If I could give just one piece of advice, it would be this: Fix your bathroom ventilation.
According to the UK’s Building Research Establishment, poor ventilation is responsible for over 70% of domestic damp problems. Bathrooms without adequate airflow trap humidity, letting it soak into walls, ceilings, and floors.
Ways to improve ventilation:
- Install or upgrade an extractor fan. Choose one with a high enough extraction rate (look for at least 15 litres per second for a bathroom). Even better, get a humidity-sensing fan that switches on automatically.
- Use the fan longer. Most people turn it off too soon. Let it run for 15–20 minutes after a shower.
- Open a window. If possible, crack it open slightly during and after a bath/shower.
- Keep the door open after use. Let the moist air escape to a better-ventilated part of the home.
Pro tip: If you’re replacing a fan, check for one with a low noise rating (below 30 decibels), so you’ll actually want to use it.
4. Control Moisture Levels with a Dehumidifier
If ventilation alone isn’t enough — or your bathroom is windowless — a dehumidifier can make a big difference.
While bathrooms are small, they can hold a surprising amount of water in the air. A single 10-minute hot shower can release 1.5 to 2 litres of moisture.
Choose a compact, bathroom-safe model (often labelled as “mini” or “designed for damp rooms”).
When to use it:
- After showers or baths.
- On damp, rainy days when windows can’t be opened.
- Overnight if you’ve had multiple showers in the evening.
Extra tip: Combine this with your extractor fan for the best results — the fan removes moist air, the dehumidifier catches what’s left.
5. Fix Leaks — Even the Tiny Ones
Not all damp is from the air; sometimes it’s coming directly from a plumbing leak. And leaks aren’t always dramatic. A dripping pipe under the sink or a loose seal around the tub can keep an area wet for weeks before you notice.
What to check:
- Around taps and shower heads for drips.
- Under the sink for small puddles or damp wood.
- Shower trays and bath edges for cracked seals.
- Toilet base for small water pools.
If you find a leak:
- Tighten fittings if they’re loose.
- Replace silicone sealant that’s cracked or mouldy.
- For larger plumbing issues, call a professional — water damage spreads faster than you think.
6. Deal with Mould the Right Way
Once damp has encouraged mould to move in, you need to evict it quickly and safely.
Why not just bleach it?
While bleach will make mould disappear visually, it often doesn’t kill the root spores, especially on porous surfaces like plaster or grout.
Instead:
- Wear protective gloves and a mask to avoid breathing spores.
- Use a mould-killing solution — hydrogen peroxide (3%), vinegar, or a specialist mould cleaner.
- Scrub gently but thoroughly.
- Dry the area completely to prevent regrowth.
If the mould covers more than 1 square metre, it’s best to get professional removal, especially if anyone in the home has allergies or asthma.
7. Upgrade Surfaces to Moisture-Resistant Materials
If your bathroom walls or ceilings are prone to damp, it might be time for moisture-resistant upgrades.
Options include:
- Moisture-resistant plasterboard (often green-coloured).
- Waterproof paint with anti-mould additives.
- PVC wall panels instead of tiles in high-splash areas.
- Epoxy grout instead of cement grout, which is more porous.
Yes, it’s an upfront cost, but think of it as buying damp insurance.
8. Keep Up with Regular Maintenance
One of the biggest mistakes people make is fixing damp once and then forgetting about it. Bathrooms are high-risk zones — without regular upkeep, damp will return.
Monthly checks:
- Look for cracked grout or silicone.
- Check for early mould growth.
- Run the extractor fan for a full 20 minutes after a shower.
Seasonal checks:
- Inspect external walls for cracks.
- Clean out ventilation grills.
- Repaint with anti-mould paint if needed.
9. Manage Temperature to Prevent Condensation
Condensation happens when warm, moist air meets a cold surface. One solution is to keep bathroom surfaces warmer so moisture doesn’t settle as easily.
Ways to do this:
- Use a heated towel rail — it warms the room and dries towels faster (wet towels are a damp magnet).
- Install underfloor heating if renovating.
- Keep the bathroom at a steady temperature instead of letting it drop too cold between uses.
It might sound small, but a couple of degrees warmer can make the difference between dry walls and a mould party.
10. When to Call in the Experts
Sometimes, DIY fixes won’t cut it. If you’ve tried improving ventilation, fixing leaks, and treating mould but the damp keeps returning, you may be dealing with:
- Hidden plumbing leaks inside walls.
- Structural issues with damp-proofing.
- Severe ventilation design flaws.
A professional surveyor can use tools like thermal imaging cameras and moisture meters to find the real cause — something you can’t always see.
Conclusion
Damp in a bathroom isn’t just about looks — it’s about protecting your home and your health. Whether it’s condensation from hot showers or a sneaky leak hiding under the sink, tackling the root cause early will save you time, money, and frustration.
I’ve personally learned that prevention is way cheaper than repair. Keep the air moving, deal with leaks quickly, and never ignore those first little spots of mould. Your bathroom will thank you — and so will your lungs.
FAQs
1. How do I know if my bathroom damp is from condensation or a leak?
Condensation usually shows as water droplets on windows and mirrors after showers and can cause mould in corners or on ceilings. A leak often leaves a specific wet patch that doesn’t dry, sometimes with a musty smell or staining.
2. Can I paint over mould in my bathroom?
No — painting over mould without removing it first will just trap the spores underneath. The mould will likely grow back through the paint within weeks.
3. What humidity level should my bathroom be?
Ideally, below 60% relative humidity. Above this, mould can start to grow quickly.
4. Will a dehumidifier completely stop damp?
A dehumidifier helps reduce moisture, but if the damp is from a leak or structural issue, it won’t solve the root cause.
5. Is mould from bathroom damp dangerous?
Yes. Mould releases spores that can trigger allergies, asthma, and other respiratory issues, especially in children and those with weakened immune systems.