How do i stop mould growing in bathroom silicone and grout? (2026)
Quick Answer
To stop mould coming back on bathroom silicone and grout, you need to do two things: remove existing contamination properly and reduce the damp conditions that let it regrow. Clean or replace badly affected sealant, keep grout and joints as dry as possible, improve ventilation, and fix leaks or gaps so moisture is not trapped behind surfaces.
Safety first
- Wear gloves and eye protection when using mould cleaners, bleach-based products or sealant removers.
- Ventilate the bathroom well when cleaning or applying sealant, and follow the product label exactly.
- Do not mix bleach with other cleaners, especially products containing ammonia or acids, because dangerous gases can be released.
- Avoid scraping so hard that you chip tiles, damage waterproof finishes or cut yourself with blades.
- If you react badly to mould or cleaning fumes, stop and get fresh air; seek medical advice for health concerns.
- Keep children and pets away from the area until cleaning residues are removed and any new sealant has cured as the manufacturer states.
When to call a professional: Stop and consult a qualified professional if mould keeps returning despite cleaning and ventilation changes, if silicone or grout failure may have allowed water behind tiles, if tiles are loose, if walls or floors feel soft, if there is a suspected plumbing leak, or if the affected area is widespread. For parts of the job a homeowner should not attempt, or if you need leak diagnosis, tiling, waterproofing or bathroom repair work in New Zealand, use Trade Directory at tradedirectory.co.nz to find a verified qualified local tradesperson.
Overview
Mould on bathroom silicone and grout is usually a moisture and ventilation problem first, and a cleaning problem second. Silicone around baths, showers and basins can develop black mould staining on the surface, but if the mould has got into or behind the sealant, cleaning alone often will not solve it. Grout can usually be cleaned if it is sound, but if it is cracked, soft or repeatedly stays wet, it may need repair or replacement. The most effective approach is to start by identifying why the area stays damp: poor extraction, condensation, slow drying after showers, leaks, failed sealant, or water getting behind tiles. Then clean what can be cleaned safely, remove and replace what cannot, and change daily habits so the area dries faster. That usually means using the extractor fan properly, opening windows when practical, wiping down wet surfaces, and not leaving bottles or mats trapping water along joints. If mould keeps returning quickly, if there is hidden damp, or if sealant failure could let water into walls or floors, treat it as a maintenance issue rather than just a cleaning issue. Persistent moisture can damage finishes and building materials over time, so dealing with the cause matters more than repeated surface scrubbing.
Who this is for
Homeowners and tenants dealing with mould on bathroom silicone, grout, tile joints and shower edges, especially where the problem is localised and there is no major leak or building damage.
What you’ll need
- protective gloves
- eye protection
- good ventilation or an extractor fan
- mould cleaner or suitable bathroom cleaner approved for the surface
- clean cloths or paper towels
- non-scratch brush or old toothbrush
- sealant remover tool if replacing silicone
- sanitary-grade bathroom silicone suitable for wet areas if resealing
- caulking gun if using cartridge silicone
- grout repair product if grout is cracked or missing
Before you start
Check whether the mould is only on the surface or whether the silicone is permanently stained, lifting, split, or letting water behind it. Read the cleaner and sealant labels carefully for surface compatibility, ventilation requirements and curing guidance. If you suspect a leak, loose tiles, rotten backing, widespread mould, or water getting into walls or floors, stop and get the underlying problem assessed before resealing.
Step-by-step
- 1
Find the moisture source
Look for the reason the area stays damp: weak extraction, no window use, condensation after showers, dripping taps, leaking shower screens, gaps in sealant, or water pooling at corners and tray edges. Check whether bottles, mats or caddies are trapping water against joints.
Why: Mould will usually return if the area still stays wet for long periods, even after thorough cleaning.
- 2
Improve drying before you clean
Start using the extractor fan during bathing and leave it running afterwards if the manufacturer allows. Open a window when practical and safe. After showers, wipe water from tile edges, silicone joints and shower trays, and reduce clutter around wet corners.
Why: Faster drying makes cleaning more effective and is one of the main ways to stop regrowth.
- 3
Clean grout and sound silicone first
Apply a suitable cleaner according to the label, allow the recommended contact time, then gently scrub grout lines and any sound, intact silicone with a soft brush. Rinse or wipe away residue as directed and dry the area thoroughly.
Why: If mould is only on the surface, cleaning may remove it without damaging finishes. Drying afterwards helps stop surviving spores from re-establishing quickly.
- 4
Decide whether silicone must be replaced
If black staining remains inside the silicone, the sealant is peeling, split, soft, mouldy underneath, or no longer bonded to the surface, remove it fully rather than repeatedly bleaching it. Cut and lift out the old sealant carefully without damaging the bath, tray or tiles, then clean and dry the joint fully.
Why: Mould can colonise within old sealant or behind failed edges, where surface cleaning cannot reach.
- 5
Repair damaged grout or joints
Rake out loose or failed grout only as needed, clean out dust and residue, and apply a suitable grout repair product or regrout following the manufacturer instructions. Let it dry and cure exactly as specified before exposing it to moisture.
Why: Cracked or missing grout holds dirt and moisture and can allow water to penetrate behind the tiled surface.
- 6
Reseal wet-area joints properly
Once the joint is clean and fully dry, apply a bathroom or sanitary silicone intended for wet areas and mould resistance, following the manufacturer guidance for preparation, application and curing. Avoid using the shower, bath or sink until the product says it is ready for service.
Why: Good-quality, correctly applied sealant blocks water from entering gaps where mould thrives and where hidden water damage can begin.
- 7
Adopt a simple prevention routine
Keep using ventilation, wipe down wet edges after use, wash away soap residue regularly, and inspect silicone and grout for early cracks or lifting. Deal with minor failures promptly instead of waiting for mould to become established.
Why: Mould prevention is mainly ongoing moisture control and early maintenance, not one-off treatment.
Why this works
Mould needs moisture, a suitable surface and time to grow. Bathrooms provide all three unless water is removed quickly and joints stay intact. Cleaning reduces existing growth, but lasting prevention comes from drying the room faster and preventing water from getting into porous grout or behind failed silicone.
Common mistakes to avoid
- Trying to bleach over stained or failed silicone instead of replacing it
- Resealing over old sealant, soap residue or damp joints
- Ignoring small leaks, loose shower screens or water pooling at tray edges
- Using abrasive tools that scratch sanitaryware or tile glaze
- Closing the bathroom up immediately after showering so condensation lingers
- Using the shower before grout or silicone has fully cured according to the product instructions
Troubleshooting
Mould comes back within days or weeks
Look for a moisture source you have not fixed yet, such as poor extraction, condensation, a leaking fitting, or water getting behind failed sealant.
Black marks stay in silicone after cleaning
Replace the silicone. Staining within the sealant body usually will not clean out completely.
Grout keeps discolouring
Check whether the grout is cracked, porous, not drying between uses, or exposed to constant soap build-up. Repair damaged sections and improve ventilation and drying.
New sealant will not stick properly
Remove all old sealant residue, soap film and moisture, then reapply only when the joint is clean and dry.
There is a musty smell even after cleaning
Investigate hidden damp behind the shower, bath panel, vanity or wall linings. Surface cleaning will not solve concealed mould growth.
Compare your options
Clean existing grout and silicone
Best for: Light, surface-level mould where joints are intact and sound
Pros: Cheaper, quicker, less disruptive
Cons: Will not solve mould inside old silicone or behind failed joints
Replace silicone only
Best for: Mouldy, stained, split or lifting sealant with otherwise sound tiling and grout
Pros: Targets a common failure point; improves waterproofing at edges
Cons: Needs careful prep and full drying; poor application can fail early
Repair grout and reseal joints
Best for: Cracked grout, missing sections, repeated wetting and visible joint failure
Pros: More complete fix; helps stop water ingress
Cons: More time-consuming and may reveal hidden damp issues
| Option | Best for | Pros | Cons |
|---|---|---|---|
| Clean existing grout and silicone | Light, surface-level mould where joints are intact and sound | Cheaper, quicker, less disruptive | Will not solve mould inside old silicone or behind failed joints |
| Replace silicone only | Mouldy, stained, split or lifting sealant with otherwise sound tiling and grout | Targets a common failure point; improves waterproofing at edges | Needs careful prep and full drying; poor application can fail early |
| Repair grout and reseal joints | Cracked grout, missing sections, repeated wetting and visible joint failure | More complete fix; helps stop water ingress | More time-consuming and may reveal hidden damp issues |
Alternatives
- Use a daily shower spray approved for the surface to reduce soap residue between deeper cleans
- Upgrade bathroom ventilation if condensation is a recurring issue
- Reduce shower splash with a better-fitted screen or curtain if water regularly hits vulnerable joints
Pro tips
- Store bottles on a rack rather than directly on shower corners and silicone edges
- Wipe down the bottom edge of shower walls and tray after the last use of the day
- Check around taps, wastes and shower screen fixings when mould keeps reappearing in the same spot
- If one bathroom is much worse than others, compare how well its fan clears steam
Legal & regulatory notes
In rented homes, responsibility for ventilation, leaks, failed sealant and mould treatment may depend on the tenancy agreement and local housing rules. Record the problem and notify the landlord or property manager promptly if building defects, leaks or failed wet-area finishes are involved.
What this guide does not cover: This guide covers general household prevention and basic maintenance for mould on bathroom silicone and grout. It does not diagnose hidden building defects, certify waterproofing, give product-specific curing times or chemical instructions, or provide medical advice about mould exposure; for those, follow the product manufacturer and consult an appropriate professional.
Cost considerations
Regular cleaning and early resealing are usually far cheaper than dealing with water damage behind tiles or sanitaryware. Costs vary widely depending on whether you only need cleaning products and sealant, or whether hidden leaks, substrate damage or bathroom repairs are discovered.
Prefer to hire a professional?
If this job is beyond a confident DIY — or the work needs to be done by a licensed professional — you can find a verified builder or licensed tradesperson through these directories of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.
Frequently asked questions
Can I just paint or seal over mouldy grout?+
No. Clean or repair the grout first and fix the moisture issue. Covering mould without removing contamination and drying the area usually leads to quick failure.
Is bleach enough to solve black mould on silicone?+
Sometimes it helps with light surface mould, but if the staining is inside the sealant or the joint has failed, replacement is the proper fix.
How often should I clean bathroom grout and silicone?+
Clean often enough to stop soap residue and damp build-up. The right frequency depends on how heavily the bathroom is used and how well it dries between uses.
Do mould-resistant silicones stop mould completely?+
They help, but they do not overcome constant damp, poor ventilation, dirt build-up or bad application. Good drying and maintenance still matter.
When is mould more than a DIY cleaning job?+
If it keeps returning quickly, covers a large area, is linked to leaks, appears behind fittings, or there are signs of damage behind tiles or linings, it needs proper investigation rather than repeated surface treatment.
Sources & references
Guidance on this page is traced to documented sources. Last checked 25 September 2026.
- CDC - Basic Facts about Mold and Dampness · government
Supports the principle that controlling moisture is the key to preventing mould growth.
The core guidance changes slowly, though individual cleaner and sealant instructions vary by product and should always be checked on the label.