A damp patch on the ceiling below the bathroom, a swollen skirting board or a musty smell next to the shower all point to the same worry: the shower is leaking. Failed sealant is one of the most common causes, but it isn’t the only one.
Before you pay for a reseal, or a new tray, it helps to narrow down where the water is getting out. This guide walks through the usual leak paths, some simple tests you can do yourself, and what a proper fix looks like when it is the sealant.
The usual places a shower leaks
- The tray-to-wall sealant along the back and sides of the tray.
- The screen or enclosure seals, where the glass meets the wall and the tray.
- The grout between wall tiles, if it’s cracked or washed out.
- The tray itself, if it’s cracked or moving because the base under it has failed.
- The waste under the tray, where it connects to the drain.
- The shower valve, pipes or riser rail fixings behind the wall.
- The tanking in a wet room, under the tiles.
Sealant and screen joints are the easiest to check and the cheapest to fix, so start there. Leave the plumbing checks for last, and call a plumber if you suspect the waste, the valve or the pipes.
Look first: what failed sealant looks like
- Gaps where the bead has come away from the tray or tile, often in the corners.
- Black mould behind the bead rather than on top of it.
- Splits along the length of the bead.
- A second layer of sealant over an old one.
- Sealant that has shrunk back, leaving a thin dark line.
Press gently along the bead. If it moves, lifts or squelches, water is getting behind it.
Simple checks you can do
These tests isolate one part at a time. Have someone watch the ceiling below, or the outside of the enclosure, while you test. Stop if water appears.
- Tray and waste only. With the shower head held low and pointing at the waste, run water into the tray for a few minutes without wetting the walls or the sealant. If it leaks now, suspect the waste or the tray.
- Tray-to-wall sealant. Run water gently along the sealant joint at the back and sides of the tray. If this causes the leak and test 1 didn’t, the sealant is the likely culprit.
- Screen joints. Spray water along the vertical joints where the screen meets the wall and along the bottom of the screen.
- Tiles and grout. Spray the tiled walls above the sealant line.
- Valve and pipes. If none of the above causes a leak but it appears when the shower runs normally, the problem may be behind the wall.
If water appears when the shower is off, it’s almost certainly plumbing, not sealant.
Symptom and likely cause
| What you see | Likely cause | Who fixes it |
|---|---|---|
| Leak only when water hits the tray edge | Tray-to-wall sealant | Sealant specialist |
| Water on the floor outside the enclosure | Screen seals or screen alignment | Sealant specialist; screen adjustment if needed |
| Leak when water hits the tray floor only | Waste or cracked tray | Plumber |
| Tray flexes or creaks underfoot | Base under the tray has failed | Plumber or bathroom fitter, then reseal |
| Loose or hollow tiles, crumbling grout | Water behind tiles | Regrout or retile, then reseal |
| Leak with the shower off | Pipework or valve | Plumber |
Need it done properly? Mr Mastic covers the South East, London and Scotland, with a one-year guarantee on every job. Call or email for a quick quote.
When it is the sealant: doing it properly
A leaking shower seal needs more than a fresh bead on top. A proper repair means:
- Cutting out all of the old sealant, including any layers underneath.
- Letting any water that has got behind the joint dry out, which can take time.
- Cleaning, degreasing and treating mould in the joint.
- Priming where the surface needs it.
- Laying a new bead of anti-fungal sanitary silicone and tooling it neatly.
- Leaving it to cure before the shower is used, usually around 24 hours.
At a Forge Wood new build in Crawley, a shower tray seal had failed after 16 months. The builder’s sealant had gone onto a gritty, unprimed surface. We took it all out, primed the surfaces and resealed with sanitary silicone. Our remedial sealant service handles leaks like this.
Why resealed showers leak again
- The new bead was laid over old sealant and never bonded.
- The joint was still wet when it was sealed.
- The tray moves because its base has failed, so every bead tears.
- The real leak was the waste, the grout or the valve all along.
- The shower was used before the sealant cured.
If a shower keeps leaking after being resealed, it’s worth having the joint stripped back and the cause found, rather than adding another layer. See why sealing over old silicone fails.
Grout and tiles
Grout isn’t waterproof on its own, but cracked or washed-out grout lets far more water behind the tiles than sound grout does. If the grout around the shower is crumbling or stained, it often makes sense to regrout and reseal at the same time. Internal corners and the tray joint should always be flexible silicone, not grout, because they move. Our regrouting service covers this.
Flats and tenements: the flat below
In flats, a shower leak quickly becomes a neighbour’s problem. In Scotland’s tenements, common in Glasgow, Edinburgh, Dundee and Aberdeen, water from a failed seal can reach the flat below through the floor. Shared repairs to common parts of tenements are covered by the Tenements (Scotland) Act 2004 and are often arranged through a property factor, but the seal around your own shower is your responsibility.
If you notice a leak, act quickly, tell your neighbour, and keep a note of what you did. It’s much easier to resolve when it’s been dealt with promptly.
Landlords and commercial showers
Shower leaks in rented homes, hotels and staff welfare facilities cause damage that costs far more than the reseal. Look at shower seals during inspections and between tenancies or guests, and reseal at the first sign of lifting or mould behind the bead. For commercial sites, resealing can be planned room by room, with early starts or out-of-hours working arranged where needed.
Quick answers
How do I know if my shower leak is the sealant?
Run water only along the sealant joint. If that triggers the leak but running water into the tray floor doesn’t, the sealant is the likely cause.
Can a leaking shower be fixed by resealing?
If the sealant is the leak path, yes, provided the old sealant is fully removed and the joint is dry before resealing.
Why does my shower still leak after resealing?
Common reasons are sealing over old sealant, sealing a wet joint, a moving tray, or a leak from the waste, grout or valve.
Do you fix cracked shower trays?
No. A cracked tray or failed base needs a plumber or bathroom fitter. We’ll tell you if that’s what we find.
Is your shower resealing guaranteed?
Yes. Every Mr Mastic job comes with a one-year guarantee.
Related services
More advice
- Can You Put New Silicone Over Old Silicone?
- Sealing a Wet Room: What Matters
- Tenement Flat Leaks in Scotland: Sealant
- Regrouting or Resealing: Which Do You Need?
- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.