Here's the uncomfortable truth about wet rooms: the parts that decide whether yours lasts thirty years or fails in three are the parts you'll never see again after installation week. The tiles, the glass, the brassware — all replaceable. The waterproof membrane and the floor drainage buried underneath them are not, at least not without ripping the whole room out. This guide explains both systems in plain English, so you know what should be happening behind your walls whether we fit your wet room or someone else does.
What tanking actually is
Tiles are not waterproof. Grout certainly isn't. A tiled shower area without anything behind it is a colander with a nice finish — water works through the grout lines, into the plasterboard, and down into whatever's below. Tanking is the continuous waterproof layer installed behind the tiles: over the floor, up the walls in the wet zones, sealed into the drain. It's the actual bathroom. The tiles are just its clothes.
In a wet room, where the whole floor is a shower tray, tanking isn't a nice-to-have on one wall — it's the entire floor, the wall areas around the showering zone, and every joint, corner and pipe penetration in between.
Liquid membranes vs sheet membranes
There are two main ways to tank a room, and a good fitter chooses based on the room rather than habit.
Liquid membranes are painted or rolled on, usually in two coats with reinforcing tape bedded into every corner, joint and penetration. They're seamless, they follow awkward shapes well, and on a properly prepared background they're excellent. Their weakness is discipline: the coats have to reach the right thickness everywhere, and corners without tape are where cheap jobs fail.
Sheet membranes come on a roll and are bonded to the floor and walls with sealed overlaps, with preformed corner pieces for the fiddly bits. Thickness is guaranteed by the factory rather than by whoever's holding the roller, which makes sheet systems very consistent — the trade-off is more joints, and every joint has to be right.
Both work. What doesn't work is either system applied straight onto dusty plasterboard, or standard plasterboard where a cement board should be, or a membrane that stops short of the shower zone's edges. The background matters as much as the membrane.
How the floor slope is formed
Water needs to travel to the drain, which means the floor needs a gradient — engineered deliberately, not hoped for.
On timber floors (most upstairs bathrooms in Teesside housing), the usual method is a former: a rigid factory-made board with the falls already built in, fitted between or over the joists so the finished floor slopes precisely where it should. On concrete floors, the gradient can be screeded in — the wet screed is shaped to falls — or a former can be set into the slab.
The gradient is shallow, roughly 1:80 to 1:50 towards the drain. Enough to move water, not enough to feel underfoot. Get it wrong and you either get standing water in the corners or a floor you can feel leaning while you brush your teeth.
Linear drains vs point drains
A point drain is the traditional square gully, usually near the centre of the showering area, with the floor falling to it from four directions — which means tiles cut diagonally around it. A linear drain is the long slot, usually against the wall or across the shower entrance, with the whole floor falling gently in one direction.
Linear drains have mostly won the argument in modern wet rooms, for practical reasons as much as looks: one fall direction suits large-format tiles (no envelope cuts), the flow rates are generous, and against-the-wall positions keep the walking area flat. Point drains still make sense in small or awkwardly shaped rooms. Either way, the drain body must be sealed into the tanking — the membrane laps into the drain's flange, so water that gets under the tiles still ends up in the waste pipe rather than the ceiling below.
How to know it was done right
You can't inspect tanking after tiling — which is exactly why we photograph it. On every wet area we build, the completed tanking is photographed before a single tile goes on: membrane coverage, taped corners, sealed penetrations, the drain connection. The customer gets the photos. It costs nothing and it means the most important stage of the job is on record instead of taken on trust.
If you're having a wet room fitted by anyone, ask for the same. A fitter who's proud of their tanking will happily photograph it. Hesitation tells you something too.
The other tell is time. Tanking has curing times between coats, and a wet room floor build-up is a sequence of stages that each need to set. A quote that promises a full wet room conversion in two days has found that time somewhere, and it's usually here.
What failure looks like — and why it's expensive
A failed wet room rarely announces itself quickly. The first signs are usually a stain on the ceiling below, a musty smell, or grout that keeps cracking along one joint as hidden moisture moves the substrate. By the time it's visible, the water has been travelling for months. The repair is not a repair — it's a strip-out, because the failed layer is underneath everything.
That's the economics of tanking in one sentence: it's a few hundred pounds of materials and a day of careful work, protecting a five-figure room. It is the single worst place in any bathroom to save money.
If you're weighing up a wet room, our wet room installation page covers the full process, and you can see finished rooms — including the stages customers never usually see — in our completed projects. Surveys are free and the quotation is a fixed written price: book one here.