What tanking actually means
Tanking is a continuous waterproof layer applied to the substrate before tiling, so any water passing through grout is contained and drains back out rather than soaking into the wall or floor.
It is a system, not a product. The membrane, the corner tapes, the pipe collars and the compatible adhesive all have to work together.
Corners, junctions and pipe penetrations are where failures happen. A perfectly painted membrane with an untaped internal corner is not tanked.
The floor and wall must be joined continuously in a wet room. A gap at that junction is the single most common cause of a leak into the ceiling below.
Where it is genuinely needed
Wet room floors and the walls around them: essential, without exception.
Shower enclosure walls: essential in our specification. A tray contains water at the base, but the wall above still gets soaked daily.
Around a bath with a shower over: essential to at least 300 mm above the shower head and 300 mm beyond the bath ends.
Behind a basin: a splashback zone is usually sufficient rather than full tanking.
The rest of the room: not required. Anyone quoting to tank an entire dry bathroom is adding cost without benefit.
Systems and costs
What each approach costs supplied and fitted, and where it belongs.
| System | Cost per m2 | Where it belongs | Lifespan |
|---|---|---|---|
| Plasterboard alone (no membrane) | £0 | Nowhere in a wet area | Fails in years |
| Liquid membrane on board | £18-£35 | Shower walls, splash zones | 20+ years |
| Tile backer board | £28-£55 | Shower walls, substrate upgrade | 25+ years |
| Backer board plus liquid membrane | £45-£80 | Our shower standard | 25+ years |
| Sheet membrane system | £40-£75 | Wet room floors and walls | 25+ years |
| Wet room former with bonded membrane | £900-£1,800 per room | Level access wet rooms | 25+ years |
How cheap quotes cut this corner
Tiling directly onto existing plasterboard in a shower area. It is faster, cheaper and it is the failure we get called out to fix most often.
Painting a membrane on flat surfaces but skipping the reinforcing tape at internal corners and around the pipe penetrations.
Relying on silicone at the tray-to-wall junction as the only line of defence. Silicone is a finish, not waterproofing.
Using a standard adhesive not compatible with the membrane, which can prevent proper bonding.
None of this is visible at handover, which is exactly why it gets left out. Our quotes list the waterproofing specification as a priced line so you can see it is there.
How to check it was done
Ask for photographs during the works. Any competent installer takes them, and the tanking stage is a natural point to record.
Ask what system is being used by name. A specific manufacturer's system with matching tapes and collars is a good sign; a vague answer is not.
Ask when tiling starts relative to tanking. Membranes have a cure time, and tiling the same afternoon is a warning sign.
Ask whether the tray-to-wall junction is taped behind the tile, not just siliconed in front of it.
We tank shower areas as standard, our own team does the tiling, and the specification appears on the fixed written quote including VAT.
Frequently asked questions
Do I need to tank a standard shower enclosure?
We treat it as essential. The tray catches water at the base, but the wall above is soaked every day and grout is porous.
Is plasterboard acceptable behind a shower?
Not on its own. It needs either a tile backer board substrate or a properly applied waterproof membrane system, ideally both.
How much does tanking add to a bathroom?
Typically a few hundred pounds for a shower area. It is a small proportion of the job and the cheapest insurance in the whole specification.
Does the whole bathroom need tanking?
No. Wet areas do. Tanking a dry bathroom wall adds cost without benefit, and we will tell you so.
How can I tell if my existing shower is tanked?
Usually you cannot without removing tiles. Soft grout, hollow-sounding tiles or a damp patch on the other side of the wall are the practical warning signs.