Most homeowners do not give their bathroom sealant a second thought — until it starts to look visibly wrong. By that point, the damage may already have begun. Knowing what to look for means you can act early, protect your bathroom, and avoid the kind of repair bills that come from water getting behind your tiles.
Here are the signs that your sealant has had its day.
1. Black or Dark Mould That Will Not Scrub Off
This is the most common reason people call us. A little surface mould can sometimes be cleaned away, but once mould has penetrated the sealant itself — which happens faster than most people realise — no amount of bleach or scrubbing will shift it permanently.
The mould keeps coming back because it is living inside the silicone, not just sitting on the surface. The only lasting fix is to remove the sealant entirely and replace it with a fresh, mould-resistant bead.
If you have been cleaning the same black patches every few weeks and they keep returning, that is a clear sign the sealant needs replacing rather than cleaning.
2. Cracking, Splitting or Gaps in the Sealant
Silicone sealant is flexible by design — it moves slightly as your bath or shower tray expands and contracts with temperature changes. Over time, that flexibility breaks down and the sealant starts to crack or split.
Even a hairline crack is enough to let water through. Once water gets behind the tiles, it can sit in the wall cavity for weeks without you knowing, leading to damp, damaged plasterboard and, in serious cases, structural problems.
Run your finger along the sealant line. If you can feel any gaps, ridges or splits, it is time to act.
3. Sealant That Has Pulled Away From the Surface
Sometimes sealant does not crack — it simply loses its bond with the tile or the bath and starts to peel away from the edge. You might notice a gap along one side, or the sealant lifting slightly when you press it.
This is a common problem in older bathrooms where the original sealant was applied over a dirty or damp surface, or where a low-quality product was used. Once the bond is broken, water will find its way through every time the shower runs.
4. Discolouration That Does Not Wash Off
White sealant that has turned yellow, grey or brown is not just a cosmetic issue. Discolouration is usually a sign of mould growth beneath the surface, soap scum that has bonded with the silicone, or simply age-related degradation.
A discoloured sealant is also a sign that the material itself is breaking down. Even if it is not yet cracking or peeling, degraded silicone loses its waterproofing properties over time.
5. Sealant That Is More Than 5–7 Years Old
Even well-maintained sealant has a lifespan. In a regularly used bathroom or shower, most silicone sealant will start to degrade after five to seven years. If yours is older than that and you have never had it replaced, it is worth having it checked — even if it looks fine on the surface.
A professional can spot early-stage deterioration that is not yet visible to the naked eye. Catching it early means a straightforward reseal rather than a more involved repair job.
What Happens If You Leave It Too Long?
The consequences of ignoring failing sealant go well beyond an untidy bathroom. Water that gets behind tiles can:
- Cause damp patches on walls and ceilings in adjacent rooms
- Lead to mould growth inside wall cavities
- Damage plasterboard and timber framing
- Create the conditions for rot in wooden subfloors
- Result in repair bills that run into hundreds or even thousands of pounds
A professional reseal typically costs between £75 and £150 depending on the job. The cost of repairing water-damaged walls and floors is considerably more.
Why Professional Resealing Makes a Difference
It is tempting to buy a tube of sealant from a DIY shop and have a go yourself. The problem is that a good reseal depends almost entirely on preparation — and preparation is where most DIY attempts fall short.
For sealant to bond properly and last, the surface needs to be completely dry, free of old sealant residue, and clean. Applying new sealant over old, damp or dirty surfaces means it will fail again within months.
A professional removes every trace of the old sealant, prepares the surface correctly, and applies a consistent, professional-grade bead that is properly tooled and finished. The result looks better and lasts significantly longer.
Get a Free Quote for Bathroom Resealing in Kent
The Mastic King covers the whole of Kent — from Maidstone and Sevenoaks to Dartford, Gravesend, Tonbridge, Tunbridge Wells and beyond. Most bathroom reseals are completed in 2–3 hours, and we always provide a clear, no-obligation quote before starting any work.
If you have spotted any of the signs above, do not wait for the problem to get worse. Get a free quote today and we will have your bathroom looking as good as new.
