You scrub, it fades a bit, and a week later it’s back. If you’ve been fighting black mould in your shower silicone, you’re not alone. And you’re probably not doing anything wrong.
If the black marks wipe off with a detergent or vinegar clean, it’s surface mould and you can keep it under control. If they’re still there after a proper clean, the mould is growing inside the silicone itself. Cleaning can’t reach it there. The only fix is to cut out the old silicone and reseal.
This guide shows you how to tell which one you have, how to clean mould safely using Victorian health advice, and how to stop it coming back. If you already know it’s past cleaning, our silicone replacement service covers homes across Melbourne.
Key Takeaways
- Mould that survives a proper clean is inside the silicone, and only replacement fixes it.
- Victoria’s Better Health Channel says mould only grows in damp, unventilated rooms, so moisture control matters most.
- A musty smell or mould spreading past the joint can point to water trapped behind the tiles (QBCC, 2026).
Why does black mould grow in shower silicone?
Victoria’s Better Health Channel puts it simply: mould will only grow in damp, unventilated rooms, and the best way to control it is to control moisture (Better Health Channel, Mould removal at home). A shower is about as damp as a room gets.
Silicone joints sit exactly where water collects: in corners, along the base, and under the screen. Soap residue and body oils settle there too and give mould something to feed on. Add a bathroom that stays steamy after every shower, and spores settle in and grow.
Isn’t wet-area silicone meant to be mould resistant? It is. Products like Selleys Wet Area Silicone contain fungicide (Selleys). But mould resistant isn’t mould proof. Over time, cleaning, wear and a constant film of soap scum give mould a foothold, and once it’s in, it can work its way into the silicone.
Victoria’s Department of Health, through the Better Health Channel, advises that mould only grows in damp, unventilated rooms and that controlling moisture is the best way to stop it. Shower silicone sits in the dampest part of the room, so poor ventilation and soap residue make it the first place black mould appears.
Can you clean black mould off shower silicone?
The Better Health Channel says household detergent or white vinegar is enough to clean mould in many cases (Better Health Channel). For surface mould on silicone, that’s where to start. Follow its safety steps:
- Ventilate. Open the window and run the exhaust fan.
- Protect yourself. Wear rubber gloves, eye protection and a P1 or P2 mask from the hardware store.
- Don’t dry brush. Brushing a dry mouldy surface flicks spores into the air.
- Clean with detergent or white vinegar. Use a microfibre cloth and rinse it often in a separate bucket of clean water.
- Give it time. Let the cleaner sit before wiping it off, then dry the area.
- Never mix bleach with ammonia, acids or other cleaners. This can release hazardous fumes.
The Better Health Channel also advises that some people shouldn’t remove mould or be nearby while it’s removed. That includes pregnant women, children, and people with weakened immune systems or chronic lung disease. If that’s you, get someone else to do it.
How do you know when to replace mouldy silicone?
The QBCC lists “peeling or discolouring silicone joints” as an early warning sign of waterproofing trouble (QBCC, Industry Snapshot Top 10 defects: Waterproofing, 2026). Discolouration that won’t clean off is exactly that. Here’s the two-minute test. Clean first. If the marks don’t shift, the mould is inside the silicone and it needs replacing. Illustration: Opal Caulking Services
Replace the silicone if:
- The black spots remain after a proper clean. They’re inside the silicone, and no product will reach them.
- The mould keeps coming back within weeks. The silicone is acting as a reservoir.
- The silicone is also peeling, split or lifting. Mould often grows along the edge where water has got behind the bead.
- There’s mould on the wall or tile beyond the joint. That can point to moisture coming from behind.
Here’s what most cleaning guides skip. Bleach-based sprays can lighten the colour of mould inside silicone, so the joint looks better for a while. The mould is still there, under the surface, and it’s back as soon as the shower gets damp again. If you’ve been bleaching the same joint every month, that’s your answer. It’s time for new silicone.
Can mould in shower silicone mean you have a leak?
The QBCC says a persistent musty smell or mould growth, particularly in bathrooms, laundries or adjoining rooms, often points to trapped moisture behind walls or floors (QBCC, 2026). Mould in the joint itself is normal wear. Mould that spreads is a warning.
Look beyond the silicone. Is there mould on the skirting outside the shower? Paint bubbling on the other side of the wall? A smell that hangs around even when the bathroom is dry? Any of those means water may be getting past the seal.
If so, replacing the silicone is still the first step, but get the shower checked as part of the job. Our guide to why a shower leaks from the bottom explains the usual causes and how to test for them.
How do you stop mould coming back after resealing?
The Better Health Channel says drying the area where mould grew is key to reducing regrowth, and the simplest way is to air the room thoroughly (Better Health Channel). After a reseal, these habits make the biggest difference:
- Run the exhaust fan during and for at least 15 minutes after every shower, or open a window.
- Squeegee or wipe the joints after showering so water doesn’t sit along the base.
- Clean gently and often. A weekly wipe with a mild cleaner beats a monthly scrub with harsh chemicals, which the QBCC advises avoiding in wet areas.
- Keep the floor waste clear so water drains instead of pooling along the joints.
When we replace mouldy silicone, we cut out every trace of the old bead, clean off residue and spores, and make sure the joint is completely dry before resealing with a mould-resistant, neutral-cure wet-area silicone. Skipping any of those steps is how mould ends up back within months.
Most shower silicone needs replacing every few years anyway. See how often you should reseal a shower for the signs to watch for.
Mould in your shower silicone that won’t shift?
Opal Caulking Services removes mouldy silicone and reseals showers across Melbourne. Send us a photo for a free online estimate, or call 0413 377 760. Book a shower reseal.
Frequently Asked Questions
Why does black mould keep coming back on my shower silicone?
It’s usually growing inside the silicone, not just on it, so cleaning only removes the surface layer. Victoria’s Better Health Channel notes mould only grows in damp, unventilated rooms, so poor ventilation speeds regrowth. If marks return within weeks of a proper clean, replace the silicone and improve airflow.
Is black mould in shower silicone dangerous?
Victoria’s Better Health Channel says mould can cause a stuffy nose, irritated eyes, wheezing or skin irritation in people who are sensitive to it. Pregnant women, children and people with weakened immune systems or chronic lung disease shouldn’t remove mould or be nearby while it’s removed. Ask your doctor if you have health concerns.
Can I use bleach on mouldy shower silicone?
You can, but read the label and never mix bleach with ammonia, acids or other cleaners, as the Better Health Channel warns this can release hazardous fumes. Bleach may lighten mould inside silicone without removing it, so marks often return. For surface mould, detergent or white vinegar is usually enough.
Can you silicone over mouldy silicone?
No. New silicone won’t bond properly to old silicone, and sealing over mould traps it under the new bead. The BPC requires wet-area sealants to be compatible with surrounding materials. Cut out the old silicone completely, clean and dry the joint, then reseal. Our shower resealing service does exactly this.
The short version
- Clean first with detergent or vinegar, following Better Health Channel safety advice.
- If black marks remain, the mould is inside the silicone and it needs replacing.
- Mould spreading beyond the joint, or a musty smell, can mean a leak.
- Good ventilation and gentle, regular cleaning keep new silicone mould free for longer.
Need the whole bathroom looked at, not just the shower? See our bathroom caulking service, or explore all our caulking services in Melbourne.