Bathroom Sealant Guide: Silicone Types, Application, and Maintenance
Good sealant keeps water out and looks clean for years. Bad sealant goes mouldy within months. Here's how to get it right.
Silicone sealant is the last thing applied in a bathroom renovation and often the first thing to fail. Mouldy, peeling, or discoloured sealant is the most common complaint we hear about bathrooms — even relatively new ones. The difference between sealant that lasts years and sealant that fails in months comes down to product choice and application technique.
Types of Bathroom Sealant
Acetoxy Silicone (Standard)
The most common type — recognisable by the vinegar smell during curing. Adequate for most bathroom applications but not the best choice for areas with constant water exposure. Available in white, clear, and various colours.
Neutral Cure Silicone
No vinegar smell and better adhesion to a wider range of surfaces including marble, natural stone, and plastics. Slightly more expensive but more versatile. Recommended for all bathroom applications.
Sanitary Silicone
Specifically formulated for bathrooms with added fungicide to resist mould growth. Dow Corning 785 and Everbuild 500 are the professional standards. Always use sanitary-grade silicone in bathrooms — general-purpose silicone will grow mould quickly.
Where Sealant Is Used
- Bath to wall junction: Prevents water getting behind the bath
- Shower tray to wall: Critical waterproofing junction
- Basin to wall: Prevents water running behind the basin
- Around shower screens: Where glass meets tile
- Internal tile corners: Movement joints where walls meet walls or floors
- Around pipe penetrations: Where pipes pass through tiled walls
Application Tips
- Surface preparation: Both surfaces must be completely clean, dry, and free of old sealant, dust, and grease. Use isopropyl alcohol to degrease
- Masking tape: Apply masking tape either side of the joint for clean edges. Remove the tape immediately after tooling — not after curing
- Gun technique: Cut the nozzle at 45° to match the joint width. Apply steady pressure for a continuous bead with no gaps
- Tooling: Smooth the bead immediately using a wet finger, a sealant finishing tool, or a spray of soapy water. One smooth pass — don't go back and forth
- Curing time: Allow 24 hours minimum before exposing to water. Full cure takes 7 days
Preventing Mould
- Always use sanitary-grade silicone with fungicide
- Ensure good bathroom ventilation — a humidity-sensing extractor fan is the best investment
- Wipe down sealant joints after showering (impractical for most people, but effective)
- Clean sealant monthly with a bathroom cleaner or diluted bleach spray
- Replace sealant when the fungicide depletes — typically every 3-5 years even with good maintenance
When to Replace
Replace sealant when:
- Mould is growing inside the sealant (surface mould can be cleaned, but mould embedded in the silicone means it's failed)
- The sealant is peeling away from the surface
- The sealant has hardened, cracked, or shrunk
- Water is getting behind the sealant (visible damp or staining)
Sealant replacement is a straightforward maintenance task that we include as part of our aftercare service. Get in touch for bathroom renovation or maintenance enquiries.
Frequently Asked Questions
How long should bathroom sealant last?
Quality sanitary silicone (Dow Corning 785, Everbuild 500) with good ventilation should last 5-8 years. In poorly ventilated bathrooms, even the best sealant may need replacing every 3-4 years.
Can I apply new sealant over old sealant?
No. Old sealant must be completely removed before applying new. New sealant won't bond properly to old silicone and will peel off.
Why does sealant go mouldy so quickly?
Three reasons: using non-sanitary silicone (no fungicide), poor ventilation (bathroom stays humid), or poor application (gaps allow water behind the sealant where mould grows invisibly).
What colour sealant should I use?
White sealant for white fixtures and tiles. Clear sealant for coloured tiles or where you want the joint to be invisible. Coloured sealants are available to match specific tile colours.
2026 Update
Checked against current best practice and UK regulations for 2026. Standards are updated periodically, so verify requirements for your project — our team works to current Building Regulations. Get expert help with your bathroom.
