5 Signs Your Mastic Sealant Needs Replacing Right Now
Most people don't think about their silicone sealant until something goes visibly wrong. By that point, water has often been getting in for months — sometimes longer. The good news is that the warning signs are easy to spot once you know what to look for.
Here are the five signs that tell you it's time to call in a specialist.
1. Black Mould That Won't Shift
This is the most common one. You've tried the mould spray, you've scrubbed it, you've left it overnight — and it's still there. Or it comes back within days of cleaning.
Surface mould can be removed. But once mould has penetrated into the silicone itself, it's there for good. The silicone is porous, and once the mould has taken hold inside the material, no cleaning product will reach it.
The only fix is to remove the sealant entirely and start fresh. New sealant applied to a clean, prepared surface — ideally with an antifungal product — will stay clean far longer than the old stuff ever did.
What to look for: Black or dark grey staining concentrated along the sealant line, particularly in corners and where the bath or shower tray meets the wall.
2. Gaps, Cracks or Splits
Silicone is flexible, but it doesn't last forever. Over time — especially in areas with movement, like around a bath that flexes when you get in — the sealant can crack or pull away from the surface.
Even a small gap is a problem. Water finds its way into the smallest openings, and once it's behind the tiles it has nowhere to go. It sits in the wall, encourages mould growth in the substrate, and eventually causes damage that's far more expensive to fix than a simple reseal.
What to look for: Any visible gap between the sealant and the tile, bath, or shower tray. Run your finger along the joint — if you can feel a ridge or catch a fingernail on it, there's a gap.
3. Sealant Pulling Away From the Surface
This is different from a crack — it's when the sealant is still intact but has lost its bond to one or both surfaces. You'll see it lifting away from the tile or the bath, sometimes with a visible gap behind it.
This usually happens when the original sealant was applied to a surface that wasn't properly prepared. The bond was never strong to begin with, and over time it's simply let go.
Once the bond has failed, the sealant isn't doing its job. Water is getting in every time the shower runs or the bath is used.
What to look for: Sealant that looks intact but has a visible gap behind it, or that moves slightly when you press it.
4. Yellowing or Brown Discolouration
Fresh silicone is white or off-white. Over time, it can yellow — particularly in kitchens where cooking fats and steam are present, or in bathrooms where certain cleaning products are used regularly.
Some discolouration is cosmetic. But heavy yellowing or brown staining that doesn't respond to cleaning is a sign that the silicone has absorbed contaminants and degraded. It won't improve with age, and it's a sign the product is past its useful life.
What to look for: Persistent yellow or brown staining, particularly concentrated in areas of heavy use or near extractor fans.
5. Bubbling, Lifting or Uneven Texture
If your sealant looks bubbly, lumpy, or has an uneven texture, it's a sign that moisture has got behind it. The bond has already failed — the sealant is just sitting there rather than actually sealing anything.
This often happens when new sealant has been applied over old sealant without removing the original first. The new product can't bond to the old one, so it fails quickly and looks worse than what was there before.
What to look for: Any texture that isn't smooth and consistent. Bubbles, lumps, or areas where the sealant looks like it's sitting on top of the surface rather than bonded to it.
What to Do If You Spot Any of These Signs
The sooner you act, the better. Water damage behind tiles is slow to develop but expensive to fix. A reseal is one of the most cost-effective pieces of maintenance you can do on a bathroom or kitchen.
The quickest way to get a price is to send a few photos via WhatsApp. We cover the whole of Kent and South East London — including Maidstone, Tonbridge, Chatham, Rochester, Dartford, Gravesend, Bromley, Swanley, Sevenoaks, Tunbridge Wells, Gillingham and Canterbury.
We'll give you an honest assessment and a fixed price before we start. No call-out fee, no obligation.
