Sunk slab treatment vs Surface-only treatment
Proper bathroom waterproofing opens the sunk, treats the slab, collars every penetration and tests before filling. Surface treatments applied over existing tiling cannot reach the penetrations, which is where almost all bathroom leaks actually originate.
The differences that actually decide it
| Criterion | Sunk slab treatment | Surface-only treatment |
|---|---|---|
| Reaches the penetrations | Yes | No |
| Treats the sunk slab | Yes | No |
| Pond tested before covering | Yes | Not possible |
| Requires opening the floor | Yes | No |
| Disruption | Several days | Hours |
| Expected outcome | Long-term | Temporary at best |
Which one, and when
Choose Sunk slab treatment
- A confirmed leak into the flat below
- Bathroom renovation with the floor open
- Any recurring wet-area leak
Choose Surface-only treatment
- Temporary containment while a proper scope is arranged
What goes wrong most often
Paying for a surface treatment over existing tiles to avoid opening the floor. The unsealed pipe penetration under the tiling is untouched, and it is almost certainly the leak.
Other decisions worth getting right
- APP membrane vs SBS membrane
Both are modified bitumen sheets applied by torch.
- Brick bat coba vs Torch-on membrane
Coba is a thick cementitious build-up that creates the fall, insulates the slab and forms the barrier all at once.
- Polyurea vs Polyurethane coating
Polyurea is spray-applied with heated plural-component equipment and gels in seconds, giving a seamless high-build film that can be walked on within the hour.
- PU injection vs Epoxy injection
The deciding question is whether the crack is moving and whether it is wet.
- HDPE membrane vs Bentonite
Both are pre-applied below-grade systems.
- Cementitious coating vs Liquid membrane
Cementitious coatings are rigid, breathable and bond well to damp concrete — which is why they suit tanks and internal tanking.
- China mosaic vs Shahabad ladi
Both are protective finishes laid over a completed terrace waterproofing layer — neither is a barrier in itself.
- Positive side (external) vs Negative side (internal)
Positive-side waterproofing sits on the face the water arrives from, so water pressure pushes it against the structure.
- Crystalline vs Surface coating
Crystalline systems penetrate concrete and grow crystals inside its capillaries, becoming part of the concrete.
Sunk slab treatment vs Surface-only treatment — questions we get asked
Sunk slab treatment or Surface-only treatment — which is better?
Neither, in the abstract. Proper bathroom waterproofing opens the sunk, treats the slab, collars every penetration and tests before filling. Surface treatments applied over existing tiling cannot reach the penetrations, which is where almost all bathroom leaks actually originate. The decision is made by the duty the system has to perform, not by which product has the better datasheet.
When should I choose Sunk slab treatment?
A confirmed leak into the flat below. Bathroom renovation with the floor open. Any recurring wet-area leak.
When should I choose Surface-only treatment?
Temporary containment while a proper scope is arranged.
What is the most common mistake people make here?
Paying for a surface treatment over existing tiles to avoid opening the floor. The unsealed pipe penetration under the tiling is untouched, and it is almost certainly the leak.
Not sure which your building needs?
That is what the inspection is for. An engineer looks at the actual substrate, exposure and movement, then tells you which system fits and why the other one does not.
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