How to Remove Black Mould from Bathroom Silicone (and Help Stop It Returning)
The black streaks creeping along your shower silicone are the most stubborn cleaning problem in any bathroom. You bleach them. They come back. You scrub them. They come back. You replace the silicone. Six months later — they come back.
Here's the truth: silicone is the perfect home for mould, and bleach is the wrong tool for the job. Here's a step-by-step guide that actually works.
Why silicone gets mouldy so quickly
Bathroom silicone (the rubbery sealant between tiles, around showers, baths, and basins) is a mould magnet for three reasons:
- It's porous — under a microscope, silicone has tiny holes that trap moisture, soap, and skin cells
- It stays wet — silicone holds water far longer than tile, especially in low-ventilation showers
- It feeds mould — soap residue, skin oils, and conditioner build up on the surface, giving mould constant food
Combine that with humid summers, and silicone becomes a mould nursery.
Why bleach can't fix it
Bleach erases the colour from mould — but it can't penetrate deep into porous silicone, and it can't remove the organic film that mould feeds on.
You spray bleach, the streaks turn white, you celebrate. Within days or weeks, the spores hidden inside the silicone reactivate, find the same food source still there, and re-grow.
What actually works: penetrate, dwell, break down
To treat mould in silicone properly, you need a treatment that:
- Penetrates deep into the silicone pores
- Dwells long enough to reach hidden spores
- Breaks down the organic film mould feeds on
Clean-chemistry mould removers like MOULDZAP are designed to do all three.
Step-by-step: remove black mould from silicone
What you'll need
- MOULDZAP (or another clean-chemistry mould remover)
- A clean cloth or paper towel
- An old toothbrush (optional, for stubborn spots)
- 30 minutes of dwell time
The method
- Dry the area first. Wipe down the silicone with a dry cloth so excess water doesn't dilute the treatment.
- Spray generously. Coat the silicone evenly along the entire seam — top, bottom, and any visible spots. Don't be shy: more is better when it comes to penetration.
- Wait 30 minutes. This is the most important step. The active ingredients need time to enter the silicone pores and break down the mould and biofilm. Walking away here is the secret most people skip.
- For stubborn spots, gently scrub. Use the toothbrush only on heavily blackened areas. Don't scrub the whole strip — let the formula do the work.
- Wipe clean with a dry cloth. No rinse needed for surface use. Keep the area ventilated afterwards so it dries properly.
- Repeat if needed. Severe mould may need 2–3 treatments over a few days. Each round penetrates deeper.
How to keep mould from coming back
Once you've cleared the mould, the goal is to prevent it from feeding again. Three habits make all the difference:
- Squeegee or wipe down after the last shower of the day to remove the moisture mould needs
- Run the exhaust fan for at least 15 minutes after every shower
- Spray weekly with a probiotic surface cleaner (a quick mist of MULTIZAP on the silicone helps stop organic film building up again)
When to replace the silicone instead
If the mould has caused the silicone itself to lift, crack, or stain permanently after multiple treatments, it's time to replace the bead. But — and this is key — re-mould will come back unless you treat the underlying cause (moisture + food). Even after re-siliconing, keep using a clean-chemistry mould spray to help stop it re-establishing.
Try MOULDZAP for stubborn silicone mould
At Thrive we match the science to the problem: probiotic biotechnology in MULTIZAP for organic residue and odour, and advanced clean chemistry in MOULDZAP and DRAINZAP for mould, scale and drain build-up.
MOULDZAP is designed to penetrate the porous surfaces bleach can't reach. No bleach fumes, no chlorine, no damaged grout — just a deep, long-lasting clean that targets the cause, not just the colour.