Bathroom Black Spots: How to Remove Mould from Silicone & Grout Permanently

Why You Can’t Just “Scrub Away” Black Spots

It’s the most frustrating thing in home cleaning. You’ve scrubbed the bath until your arms ache. The tiles are gleaming. The tap chrome is shining. But those stubborn black spots on the white silicone sealant? They haven’t budged an inch.

We see this every day in London homes. A client in Hackney told us last week she’d spent £50 on different “miracle” sprays, and the spots were still laughing at her. The reason isn’t that you aren’t cleaning hard enough. It’s that you are cleaning the surface, but the mould isn’t on the surface.

Here is the mechanics of what’s happening:

• Silicone Failure: Over time, the waterproof seal begins to lift slightly at the edges. Moisture gets behind it. The mould grows underneath the silicone. You can’t scrub it off because there is a layer of rubber between your brush and the fungus.
• Grout Porosity: Grout looks hard, but it acts like a stiff sponge. It absorbs water. When mould roots grow into these microscopic holes, surface wiping just takes the top off, leaving the root system alive and well inside the cement.

Stop Using Bleach (It Often Makes Things Worse)

If you take one thing away from this article, let it be this: Bleach is not the answer for porous surfaces.

We know, your grandmother swore by it. And yes, if you spray bleach on black grout, it turns white. Success? Not really. You’ve just bleached the colour out of the mould. You haven’t killed the root structure deep in the grout.

In fact, bleach contains a lot of water. When the chlorine evaporates (which happens quickly), it leaves that water behind, feeding the roots that survived. We often see mould return twice as strong a few weeks after a heavy bleach session.

Step-by-Step: Removing Mould from Grout (The Right Way)

Before you rip everything out, try this method for your grout lines. It uses acidity to penetrate the pores rather than just bleaching the surface.

What You Need:

• White vinegar (distilled)
• Bicarbonate of soda
• A stiff toothbrush (not an old soft one)
• A spray bottle

The Method:

The Nuclear Option: Replacing Mouldy Silicone

If the black spots are on the rubbery sealant around your bath or shower tray, cleaning is usually a waste of time. The mould has dyed the silicone black. You need to replace it.

Don’t be intimidated—this is a job you can do on a Saturday morning.

1. Strip the Old Sealant

Use a sharp Stanley knife or a dedicated sealant removal tool (costs about £5 at a hardware store). Slice along the top and bottom edges. Pull the strip out. It usually comes away in long, satisfying ribbons.

2. Clean the Gap (Most Important Step)

Once the rubber is gone, you’ll see grime left behind. Clean this area with white spirit or rubbing alcohol. It must be bone dry and grease-free. If there is leftover black mould on the actual wall or bath edge, treat that with a fungicidal wash before resealing.

3. Apply the New Bead

Buy a high-quality “Sanitary Silicone” containing a fungicide. Don’t buy the cheapest tube. Cut the nozzle at a 45-degree angle. Squeeze with steady pressure. Use a wet finger (dipped in washing-up liquid) to smooth it down in one continuous motion.

Keeping Your Bathroom Spot-Free

Okay, you’ve cleaned the grout and replaced the silicone. It looks brand new. How do you stop this happening again in six months?

Mould needs moisture to survive. Deprive it of water, and it can’t grow. It really is that simple, though hard to execute in a busy family home.

• The Squeegee Habit: Keep a squeegee in the shower. Use it on the glass and tiles after every single shower. It takes 20 seconds but reduces moisture by 70%.
• Dry the Sealant: If water pools around the back of your taps or in the corners of the bath, dry it with an old towel. Standing water is the enemy.
• Ventilation: We sound like a broken record, but open the window. If you don’t have a window, check your extractor fan. Hold a piece of toilet paper up to it while it’s on. If it doesn’t hold the paper, the fan is clogged or broken.
• Don’t Leave Wet Bottles: Shampoo bottles sitting on the corner of the bath trap water underneath them. This is a classic starting point for black spots.

When DIY Isn’t Enough

Sometimes, despite your best efforts with vinegar pastes and new silicone, the mould comes back fast. Or perhaps the black spots aren’t just on the sealant, but creeping up the painted walls and ceiling too.

This usually indicates a humidity issue that goes beyond splash water. It could be a hidden leak behind the tiles, or poor building ventilation that requires a mechanical solution.

If you find yourself constantly fighting a losing battle against regrowth, you might need professional mould removal services. We don’t just clean; we diagnose the moisture source.

Common Questions About Bathroom Mould