Waterproofing and Tanking: The Hidden Step That Protects Your Bathroom
Tanking is invisible once the tiles go on, but it's the single most important protection for your bathroom. Here's why cutting corners on waterproofing always costs more in the long run.
If there's one area where cutting corners in a bathroom renovation will come back to haunt you, it's waterproofing. Tanking — the process of applying a waterproof membrane to walls and floors in wet areas — is completely invisible once the tiles are installed. But without it, water will eventually find its way through grout joints, behind tiles, and into the building fabric, causing damage that can cost thousands to repair.
What Is Tanking?
Tanking involves applying a waterproof barrier to the substrate (walls and floor) before tiling. The most common method in modern bathroom renovation uses a liquid-applied membrane — a flexible, paintable waterproof coating that bonds to plasterboard, cement board, or plaster.
The process typically involves:
- Applying a primer coat to the substrate
- Embedding waterproof tape into all internal corners, junctions, and pipe penetrations
- Applying two coats of liquid membrane (each coat in a different colour to ensure full, even coverage)
- Allowing the membrane to cure fully before tiling
Where Should You Tank?
At minimum, you must waterproof:
- The entire shower area — walls to full height and floor
- All walls behind a bath
- The floor around the toilet
Many professionals (ourselves included) recommend tanking all walls and the entire floor in a bathroom. The additional material cost is modest (perhaps £50-£100 extra), and it provides complete protection against any moisture ingress from any source.
What Happens Without Proper Tanking?
We regularly see the consequences of skipped or inadequate waterproofing:
- Damp patches appearing on the other side of bathroom walls
- Tiles lifting and debonding as moisture degrades the adhesive
- Black mould growth behind tiles (only discovered when tiles are removed)
- Structural timber damage in joists and studwork
- Damage to downstairs ceilings in flats and two-storey properties
In every case, the repair involves stripping the bathroom back to the substrate and starting again — far more expensive than doing it properly the first time.
How to Check Your Fitter Does It Properly
Ask to see the tanking before tiles go on. A quality fitter will show you the completed membrane as a point of pride. If they're reluctant to show you, or claim it's "not necessary for your bathroom," consider that a red flag.
All Step Ahead bathroom renovations include full waterproofing as standard — get in touch for a quote that includes proper protection from day one.
2026 Update
Reviewed for 2026. Guidance here remains current; if in doubt about your own bathroom, our team is happy to help. Get in touch for a free quote.
