There are two very different problems behind most bathroom leaks, and they cost very different amounts to fix.
One is failed silicone. The bead around your shower or bath has gone brittle, lifted or split, and water is getting into the joint behind it. That is a few hundred dollars and half a day.
The other is a failed waterproofing membrane. The sheet system underneath your tiles, installed before they were laid, has been breached. That is a bathroom strip-out, and it runs into the thousands.
The frustrating part is that from inside the bathroom, the early signs look almost identical. Below are the 10 signs that separate them, how we work out which one you have, and what each costs.
Quick answer: If the damage is confined to the bathroom and shows up around a joint, such as mould in the bead, a lifting edge or dampness at the base of the shower screen, it is usually the silicone and a reseal will fix it. If water is appearing outside the bathroom, in the room below, in an adjoining wall, or in the ceiling underneath, the waterproofing membrane has almost certainly failed and resealing will not help. A silicone bead seals a joint between two surfaces. It is not a waterproofing system and cannot replace one.
Start Here: What Is Your Symptom Telling You?
| What you can see | Most likely cause | Typical fix |
|---|---|---|
| Black mould in the silicone that returns days after cleaning | Silicone past its life | Reseal |
| Silicone lifting or peeling at one edge | Silicone adhesion failure | Reseal |
| Damp patch on the floor just outside the shower | Silicone, or a screen not draining correctly | Reseal, check screen |
| Loose or drummy tiles in the shower floor | Water sitting under the tiles | Investigate membrane |
| Water stain on the ceiling of the room below | Membrane failure | Strip out and re-waterproof |
| Damp or bubbling paint on the other side of the shower wall | Membrane failure | Strip out and re-waterproof |
| Musty smell with no visible mould | Water trapped in the substrate | Investigate membrane |
| Grout crumbling across the whole floor | Movement or long-term saturation | Investigate, may be both |
The rule of thumb: if the water is staying in the bathroom, suspect the silicone. If it is leaving the bathroom, suspect the membrane.
5 Signs It’s the Silicone (the Cheap Fix)
Good news if these are what you are seeing. All five point to a reseal.
1. The mould is in the bead, not on it
Clean it hard. If the black comes back within a few days, the mould has grown into the silicone rather than sitting on the surface. Once it is through, no cleaning product will remove it, because the problem is inside the material. That is the single most common reason bathrooms get resealed.
2. The bead has lifted along one edge
Run a fingernail along the silicone where it meets the tile. If it lifts, or you can see a dark line behind it, the seal has failed and water is tracking in behind. Water that gets behind silicone does not dry out.
3. It has gone hard
Cured silicone should give slightly under pressure. If it feels like plastic, it has lost its flex and stopped absorbing the small movements every bathroom makes. Brittle silicone cracks, usually at corners first.
4. The damp is right at a joint
Wet patches at the base of the shower screen, along the bottom of the bath, or where the floor meets the wall all point at the joint rather than the system underneath.
5. The bathroom is roughly 8 to 15 years old and has never been resealed
Silicone in a wet area has a service life of around ten years, sometimes less in a heavily used family bathroom. If it has never been done, it is simply due. Our post on the 7 signs your bathroom caulking needs replacing goes through this in more detail.
5 Signs It’s the Waterproofing (the Expensive One)
These five mean the membrane under the tiles has been breached. Resealing will not fix any of them.
1. Water is appearing outside the bathroom
A stain on the ceiling below, damp in an adjoining wall, lifting floorboards in the next room, or bubbling paint on the other side of the shower wall. Silicone failure does not do this. Water has got through the floor or wall system.
2. Tiles sound hollow when tapped
Tap across the shower floor with a knuckle. A drummy, hollow note means the tile has debonded from the substrate, usually because water has been sitting under it.
3. Grout is failing across the whole floor, not just at the edges
Edge grout cracks from movement. Grout crumbling everywhere usually means the bed underneath has been saturated for a long time.
4. There is a smell but nothing visible
A persistent musty smell with no mould you can find means water is sitting somewhere you cannot see, inside the wall or under the floor.
5. It was resealed recently and the problem came back
This is the clearest sign of all. If someone resealed the bathroom within the last year or two and the leak returned, the silicone was never the cause. A reseal over a membrane failure buys a few months at most, because the water was never coming through the joint.
A word on that last one. Resealing a bathroom that has a membrane problem is the most common wasted spend we see. It is not always dishonest, because the symptoms overlap early on, but it does mean paying twice. If a contractor quotes a reseal without asking whether water is showing up outside the bathroom, ask them why.
How We Work Out Which One You Have
A proper diagnosis takes about twenty minutes and does not involve removing anything.
We start outside the bathroom. The room below, the adjoining walls, the ceiling underneath. If there is no moisture anywhere outside the wet area, the membrane is very likely intact and the problem is at a joint.
Then the joints themselves. Every silicone line gets checked for adhesion, flexibility and mould penetration. Lifting at an edge, splits at the corners and mould growth inside the bead all tell us the seal has failed.
Then the tiles. Tapping across the shower floor and lower walls finds debonded tiles, which usually means water has been sitting underneath.
Then a moisture reading if needed. A meter on the substrate and adjacent walls confirms whether water has travelled beyond the joint.
What this rules out matters as much as what it finds. A reseal on a bathroom with a compromised membrane is money spent for nothing, and the only way to avoid that is to look properly first.
What Each Fix Costs
| Problem | Fix | Starting price | Disruption |
|---|---|---|---|
| Failed silicone, single shower | Strip out and reseal | From $250 | A few hours |
| Failed silicone, full bathroom | Full reseal | From $400 | Half a day |
| Shower screen seal and base | Reseal plus screen check | From $250 | A few hours |
| Membrane failure, shower only | Remove tiles, re-waterproof, retile | Several thousand | Days, bathroom unusable |
| Membrane failure, whole bathroom | Full strip-out and re-waterproof | Significantly more | A week or more |
The gap between those two halves of the table is the entire reason this post exists. Our shower resealing cost guide covers the reseal side in detail, and the waterproofing cost guide covers the other.
Quick Roundup: Silicone vs Waterproofing
| Failed silicone | Failed waterproofing | |
|---|---|---|
| Where the damage shows | Inside the bathroom, at joints | Outside the bathroom |
| How fast it appears | Gradual, mould first | Often sudden, as a stain elsewhere |
| Tiles | Sound solid | May sound hollow |
| Typical age | 8 to 15 years | Any age, often a build defect |
| Fix | Reseal | Strip out and re-waterproof |
| Cost | Hundreds | Thousands |
| Does resealing help? | Yes, it is the fix | No, it hides it temporarily |
Silicone is not waterproofing. A bead seals the joint between two surfaces. A membrane is a system installed under the tiles before they are laid. They do different jobs, and one cannot stand in for the other. Any contractor who tells you a reseal will fix a leak showing up in the room below is either guessing or hoping.
Bathroom Leak FAQs
Can you tell over the phone which one I have?
Usually we can narrow it down. The question that separates the two fastest is whether water is appearing anywhere outside the bathroom. Photos of the affected area help as well. But a proper answer needs someone on site.
How long does a bathroom reseal take?
A single shower is a few hours. A full bathroom is around half a day. Silicone is touch dry within a few hours but needs a full cure before heavy water exposure, so leave the shower unused overnight.
My bathroom is only three years old. Can the waterproofing already have failed?
Yes, and it is more common than people expect. Membrane failures are usually build defects rather than wear, so they show up early rather than late. If the home is still within its builder’s warranty period, that is worth checking before paying for anything.
Will resealing stop the leak while I save up for the bigger job?
If it is a membrane failure, not really. Water is getting in somewhere other than the joint, so sealing the joint does not interrupt the path. It can mask the symptom briefly, which usually makes the eventual damage worse rather than better.
Do you do the waterproofing as well, or just the silicone?
Both. That is partly why we are comfortable telling you when a reseal is not the answer, because we are not trying to sell you the cheaper job either way.
What if the leak is on a balcony rather than a bathroom?
Similar logic, different causes. Our balcony leak repair guide covers the seven most common causes.
Do you service my area?
We work across Melbourne, including Coburg, Northcote, Brighton, Glen Iris, Sunbury, Hadfield and the surrounding suburbs. See our service areas.
Get Your Bathroom Leak Diagnosed
If something in your bathroom is leaking and you are not sure how serious it is, we can tell you. The inspection takes about twenty minutes and you will get a straight answer about whether this is a few hundred dollars or a few thousand.
Professional Caulking Group has been sealing and waterproofing Melbourne homes for over seven years, with more than 580 five star Google reviews.
Call 0435 803 646 or request a quote online.