The "New Year Refresh": The Professional Way to Remove Black Mould

Why scrubbing doesn't work. The chemical secret to dissolving old silicone and applying a mould-proof barrier for 2026.

It is January 2026. You have scrubbed your shower tray with bleach until your eyes watered, but those black spots in the corner are still staring back at you. In my 15 years as a tiler—working from the damp cellars of Bavaria to the humid en-suites of Cork—I have learned that Irish homeowners work too hard. You are trying to clean something that is already dead.

When silicone turns black, it has failed. The fungicide has washed out, and the mould is eating the rubber. You cannot clean it; you must evict it. But most people do this wrong. They scrape it out with a knife, apply new silicone, and watch it peel off two weeks later.

Here is the German method to doing it once, so you don't have to do it again until 2035.

Step 1: The Surgical Cut (Mechanical Removal)

Put down the butter knife. You need a tool that cuts, not just scrapes. Old silicone is tough.

I use the OTTO Cartridge Cutter for this. While it is designed to open tubes, the integrated blade is perfect for slicing the bulk of the old bead away from the tile without scratching the enamel of your expensive shower tray.

The Goal: Remove 90% of the rubber. Do not try to scrape every last film off yet—that is what the chemistry is for. If you scrape too hard with a metal blade, you will scratch your tiles, and those scratches will become new homes for mould.

Step 2: The Chemical Secret (Dissolving the Residue)

This is the step 95% of DIYers skip.

When you pull old silicone off, it leaves a thin, invisible layer of grease and rubber on the tiles. New silicone will not stick to old silicone. If you apply fresh sealant over this film, water will creep behind it within months (capillary action), and the black mould will return.

You must use a Silicone Sealant Remover Gel. You paint this onto the remaining residue and wait. It breaks down the molecular chain of the rubber, turning it into a soft paste that you can wipe away with paper. It resets the surface to "factory clean."

Step 3: The "Mould-Proof" Barrier

Now that the joint is sterile, you need to seal it. But do not grab the €5 tube from the bargain bin. Cheap silicone is filled with chalk and solvents. It shrinks as it dries (pulling away from the tile) and the fungicide washes out in weeks.

For premium tiling projects in Ireland, I exclusively use Ottoseal. It is pure silicone with a fungicide that is locked into the material.

For Modern Bathrooms (Matte Finish)

If you have the trendy "concrete look" or slate tiles that are popular in 2026, a shiny plastic-looking sealant looks terrible.

I recommend Ottoseal S100 Matt Premium.

• Why: It has a unique matte skin that matches the texture of grout
  
  
• Benefit: It hides water spots and soap scum far better than gloss silicone

For Natural Stone (Marble/Granite)

If you have a marble wet room, standard silicone will ruin it. The oils in the sealant will soak into the stone and leave "picture frame" stains.

You must use Ottoseal S70 Natural Stone Silicone.

• Why: It is guaranteed not to stain porous stone
  
  
• Benefit: It comes in stone-specific colours like "Carrara White" and "Sandstone"

Step 4: The Perfect Finish (No Saliva!)

Please, do not lick your finger to smooth the silicone. Your saliva contains bacteria that you are effectively injecting into the fresh sealant.

Use a profiling tool. The OTTO Fugenfux® Set of 4 is the industry standard. These little blue tools allow you to scrape off the excess silicone at a perfect angle (chamfer). This shape ensures water runs off the joint quickly, preventing mould growth.

The Technique: Spray the fresh bead with a smoothing agent (water + dash of washing up liquid), then glide the Fugenfux along the rails. It collects the excess and leaves a factory finish.

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3 Real-Life Case Studies

1. The "Forever Leaking" Tray (Dublin)

Problem: A client in Clontarf had re-sealed their shower tray 4 times in 2 years. It always leaked.

Diagnosis: They were using a Stanley knife to remove the old silicone but leaving the invisible film behind. The new silicone was just sitting on top of the old grease, not bonding to the tray.

Solution: We used chemical remover gel to strip the tray back to the bare acrylic. We re-sealed with Ottoseal S100 Premium Glossy in White.

Result: 3 years later, zero leaks.

2. The "Scrubbed" Grout (Limerick)

Problem: A homeowner used a wire brush to remove mould from their silicone.

Diagnosis: The wire brush scratched the glaze off the adjacent tiles. The mould then grew into the porous clay of the tile itself.

Solution: We had to grind out the tile edge. We replaced the seal with a wider bead of Ottoseal S100 Matt to cover the damage.

Lesson: Never use abrasives near tiles. Use chemistry.

3. The "Stone Stain" Nightmare (Galway)

Problem: A beautiful polished Crema Marfil marble floor had dark grey shadows around every edge.

Diagnosis: The tiler had used a cheap acetoxy (vinegar-smelling) silicone. The acid etched the stone and the oils stained it.

Solution: We cut out the silicone and used a poultice to draw out the oil (only partially successful). We re-sealed with Ottoseal S70 in "Jasmine" to prevent further damage.

Lesson: If you have stone, S70 is the only choice.

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Pros & Cons: Chemical vs. Mechanical Removal

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7 FAQs: Removing Silicone in 2026

1. Can I just put new silicone over the old layer?

Nein. Never. It will not bond. Moisture will get trapped between the two layers, creating a "mould sandwich." You must remove 100% of the old sealant.

2. Does vinegar dissolve silicone?

Vinegar can soften fresh silicone slightly, but for cured, rubbery silicone that has been there for years, it is useless. You need a specialized solvent depolymerizer.

3. How long do I leave the chemical remover on?

It depends on the thickness, but typically 15 to 30 minutes. If the silicone is very old and hard, you may need to apply it, cover it with cling film (to stop it drying out), and leave it for an hour.

4. What is the best tool for smoothing?

Your finger is the worst tool. It creates a concave "U" shape that holds water. The OTTO Fugenfux creates a flat triangular profile that sheds water. Plus, it keeps your hands clean.

5. Why is Ottoseal S100 better than the €5 stuff?

The €5 stuff is "extended" with solvents. When the solvents evaporate, the bead shrinks. S100 is pure silicone. It stays flexible and the fungicide is of a much higher grade.

6. Can I use S100 for my windows too?

For glass and windows, you want a specific glazing sealant like Ottoseal S10 Glass Sealant. It has higher UV resistance for exterior weather.

7. How long must I wait before showering?

With Ottoseal, it is touch-dry in 20 minutes, but you must wait 24 hours for full cure. Do not cheat this time!

Conclusion

Removing silicone is not a glamorous job, but it is the single most effective "New Year Refresh" you can do for your bathroom. It brightens the room more than painting the walls.

But remember: you cannot fight chemistry with elbow grease. Dissolve the old, prep the surface, and seal it with the best.

Get all your silicone needs for demanding tiling projects in Ireland sorted at sealantstore.ie. Stop scrubbing and start sealing like a pro.


There is no 'good enough', there is only correct.   ;-)