Mould creeping along bathroom seals, kitchen edges, or around windows is more than unsightly — it can affect air quality and damage finishes. A mould-resistant silicone sealant is one of your best DIY defences. Used properly, it offers a flexible, waterproof barrier that actively suppresses mould growth.
For London homeowners dealing with damp, condensation, or ageing properties, this post will guide you through:
- Top Mould-Resistant Silicone Sealants
- How mould-resistant silicones work
- Where to use them
- What to look for
- Step-by-step application tips
- When to call in a damp & mould professional
- How to Seal a Bath Properly (with Water in It)
Let’s get started.
Top Mould-Resistant Silicone Sealants UK (2025) — DIY Reviews & Links
Here’s a comparison table of well-reviewed sealants available in the UK, with strengths, trade-offs, and direct purchase links:
| Product | Best Use | Key Features | Approx. Price | Pros | Cons | Buy Link |
|---|---|---|---|---|---|---|
| UniBond Anti‑Mould Sealant | Bathrooms, kitchens | Anti-fungal, waterproof, quick-dry | ~£6–£9 | Strong DIY choice, widely available | May yellow over time | Amazon UK BM Store B&Q Wickes |
| Everbuild Everflex 200 / LMA Silicone | Bathrooms & general sealing | Flexible, durable | ~£5–£7 | Good colour range, resilient. A robust option with a wide range of colours and good resistance. | Slightly firmer to tool | sealantsupplies.co.uk Amazon UK Toolstation |
| DOW Corning / Dowsil 785 Sanitary Silicone | Trade / specialist bathrooms | Sanitary-grade, anti-bacterial | ~£8–£11 | Excellent long-term performance. A professional grade sealant often praised on trade forums. | Limited colours | Toolstation Selco Builder Depot |
| Mapei Mapesil AC Silicone Sealant | Tiles, showers | BioBlock® tech, tile-industry standard | ~£7–£10 | Good colour coordination. A tile industry–favoured option; many users like its consistency and performance. Variation with enhanced mould resistance built in. | Slower cure in thick beads | B&Q Screwfix sealantsupplies.co.uk |
| No Nonsense Sanitary Silicone | Quick DIY fixes | Budget-friendly, neutral cure | ~£4–£6 | Good for small jobs. A neutral cure silicone, beneficial where acid smells or corrosion must be avoided. | Shorter lifespan | Screwfix |
Prices are indicative and may fluctuate. Always check current listings and stock.
Other brands:
- Bostik S31 Sanitary Silicone Sealant — Another trade-level option with good acceptance in the UK market.
- UniBond Re‑New Silicone Sealant — Designed for re-sealing and refreshing existing joints.
How Mould-Resistant Silicone Sealants Work
To spot the best sealants, it helps to understand the science behind them.
1. Fungicides / Biocides
What makes a silicone “mould-resistant” is the addition of fungicides or mildewcides. These kill or inhibit mould spores as they try to settle, preventing visible black mould or patchy discolouration.
2. Waterproof Formula
Even a fungicide can’t help if moisture seeps behind the seal. A good silicone forms a continuous, waterproof, flexible bead that blocks water ingress and helps keep substrates dry.
3. Hygienic, Smooth Surface
Cured silicone is non-porous and smooth. Mould has less to feed on, and cleaning becomes easier. The fewer micro-voids, the less chance for spores to hide.
4. Durability & Elasticity
Buildings shift, surfaces expand and contract with temperature changes. A high-quality silicone remains elastic, resisting cracks or gaps that let in water.
Where to Use Mould-Resistant Silicone
You’ll get the most benefit in zones with frequent moisture or condensation:
- Around baths, shower trays, and shower screens
- Between tiles and sanitaryware
- Around sinks, splashbacks, and kitchen worktops
- Around UPVC, glass, ceramic, and stainless fixtures
- Low-level wall transitions in wet rooms
In short: seal where water, steam, or splash risks are high.
What to Look For in a Quality Sealant
Before buying, check the following:
- Clearly labelled fungicide / anti-mould action
- Sanitary / bathroom grade / “wet area”
- Elastic movement capability (for expansion, contraction)
- Neutral cure (low odour) for indoor comfort
- Colour stability (resistance to yellowing, staining)
- Quick cure / touch dry times
- Warranty or long-term performance claims
Don’t judge only by price—surface prep and application are equally critical.
DIY Application Guide: Step by Step
Use these best practices to get a long-lasting finish:
- Remove all old sealant
Use a sharp knife or scrapers. Residue traps spores. - Clean thoroughly
Degrease with isopropyl alcohol or an anti-mould cleaner. Remove soap scum and oils. - Ensure surface is completely dry
Any residual moisture undermines adhesion. - Mask edges for clean lines
Use painter’s tape on both sides of the joint. - Apply the sealant
Cut nozzle at 45°, apply in a steady bead, pushing the gun forward. - Smooth the bead immediately
Use a wetted tool or a finger (with soapy water) before film forms. - Cure fully before water exposure
Many sealants need 24–48 hours. Consult the label. - Ventilate during curing
Good airflow helps curing and reduces condensation risk.
Mistakes DIYers Often Make
- Applying new silicone over mouldy or damp surfaces
- Skipping cleaning or degreasing step
- Poor ventilation during & after cure
- Beads that are too thin (ineffective) or too thick (slow cure)
- Using indoor sealant in exterior or high-movement zones
If mould returns quickly, it’s often a sign of deeper moisture — that’s where a professional survey is needed.
Highlights & Use Cases
- UniBond is often the go-to DIY pick: solid performance, easy to find, and reliable.
- Everbuild Everflex / LMA line offers good flexibility and colour matching for bathrooms.
- DOW Corning 785 / Dowsil is preferred by tradespeople for longevity and resistance in demanding conditions.
- Mapei Mapesil AC is excellent for tile installers who want colour-matched silicone joints.
- No Nonsense is a good budget option for small repairs or tight budgets.
Here’s a smoother, blog-ready rewrite that fits naturally into your post’s tone and structure (clear, friendly, DIY-oriented, and optimised for readability):
Why Filling the Bath Before Sealing Is Crucial
When sealing a bathtub, one small but essential step often gets skipped — filling the bath with water first. It might sound unnecessary, but this trick can make all the difference between a seal that lasts for years and one that cracks after a few uses.
Prevents Cracking and Gaps
A bathtub naturally flexes and sinks slightly under weight — especially when filled with water and a person. If you apply sealant while the tub is empty, it’s sitting higher than it will be in normal use. Once filled later, the tub shifts downward, stretching and stressing the sealant bead until it cracks or separates. Filling the bath before sealing ensures the silicone cures in that “weighted” position, keeping it flexible and intact when the bath is used.
Allows for Proper Expansion and Contraction
Sealant needs to expand and contract with small movements in the bath and tiles. Sealing while the bath is full allows it to cure at its lowest, most stressed point, meaning when it rises slightly again, the sealant remains under minimal tension — extending its lifespan.
How to Seal a Bath Properly (with Water in It)
- Clean and prepare the area
Remove any old or mouldy sealant completely. Wipe down the surface with an alcohol-based cleaner and let it dry. - Mask the edges
Apply masking tape neatly along the bath edge and tiles to achieve clean, straight lines and prevent mess. - Fill the bath with water
Fill the tub to a substantial level. This weight causes the bath to settle slightly into its normal “in-use” position. - Apply the sealant
Cut the nozzle at a 45° angle and run a smooth, even bead of mould-resistant silicone sealant along the joint between the bath and tiles. - Smooth the bead
Use a sealant finishing tool, or a wet finger dipped in soapy water, to create a neat, slightly concave line that will shed water easily. - Let it cure (with water still in the bath)
Leave the bath filled for at least 24 hours so the silicone can fully cure in position. This ensures maximum adhesion and flexibility. - Drain the bath
Once fully cured, gently drain the water. The bath will lift slightly, tightening the seal just enough to create a durable, watertight finish.
✅ Pro Tip:
Pair this step with a sanitary-grade, mould-resistant silicone like UniBond Anti-Mould Sealant or Dowsil 785 Sanitary Silicone (Toolstation). These sealants are specifically designed for wet areas and provide a long-lasting, flexible barrier against mould and moisture.
FAQ
Can I reapply new silicone over old?
No. Always remove the old bead entirely. Any remnant reduces adhesion and can trap spores.
Should I fill the bath before sealing?
Yes. When filled, the bath settles. Sealing while empty might lead to cracks when it shifts later.
How long does mould-resistant silicone last?
Quality sealants can last 5–10 years, depending on usage, ventilation, and maintenance.
Why does bathroom mould keep returning?
Frequently, mould resurfaces because the root cause — humidity, leaks, or trapped moisture behind walls — hasn’t been addressed.
When DIY Isn’t Enough — Call in the Professionals
Sealants help with surface mould and small joints. But if you’re dealing with:
- Persistent musty smells
- Black mould on walls or ceilings
- Peeling paint or bubbling plaster
- Runaway condensation on windows
- Hidden damp in walls
— then it’s time to bring in a specialist. In London, our team can perform a full damp survey, diagnose root causes (rising damp, lateral dampness, condensation), and apply proven treatments. Sealant can be your first line of defence, but real control comes from fixing structural moisture issues.
For DIYers:
- Select a reliable mould-resistant silicone (see the table above)
- Apply with care and full preparation
- Use it alongside good ventilation and cleaning
But don’t over-rely on it. Strong, persistent mould often signals deeper water issues that only professionals can resolve.
Take action:
Book a Damp & Mould Survey in London — get to the root of the problem, not just the visible mould. Our team offers guaranteed treatments, clear reports, and lasting results.
Let your sealant work for you — but rely on expertise when needed.