Wet rooms & level-access showers

How does Wet rooms & level-access showers work, step by step?

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   Step 1: Design the floor build-up and the drainage together

   The room is designed before it is built. The designer and the services engineer settle the drain type and position, the direction and extent of the falls, the finished floor level relative to the room outside, and how the floor structure accommodates all of it - a recess in the slab, a ramped screed, a preformed sloped former, or a timber floor cut and reinforced to take a drain body. The waterproofing system is selected as a system, with its own tapes, corners and collars, and the tanked zones for floor and walls are drawn rather than left to judgement. Anything decided after the structure is cast is a compromise.

2. 2

   Step 2: Prepare a sound, stable substrate

   Waterproofing bonds to what is under it, so the substrate is made sound before anything else. Concrete and screed are checked for soundness, cleanliness and dryness and made good. Timber floors are stiffened and overlaid with a suitable board, because deflection cracks membranes and finishes alike. Board walls in the wet zone are replaced with a board suited to wet areas, fixed at the centres the board requires with joints supported. Dust, laitance, curing residue and paint are all removed. A membrane applied over a poor substrate fails at the substrate and takes the blame itself.

3. 3

   Step 3: Form the falls to the drain

   The falls are built to the design - to a linear channel at a wall or a threshold, or to a centre gully with the floor falling from all sides. The drain body is set first, at its finished level, secured so that it cannot move, and its flange prepared to receive the membrane. The screed or former is then built to it and checked with a level and a straightedge across the whole floor, not just near the drain, because a flat spot or a back-fall anywhere leaves standing water and the tiles will show it. The gradient itself comes from the designer, and site enthusiasm neither adds nor removes it.

4. 4

   Step 4: Apply the tanking as a continuous system

   The membrane is applied to the floor and up the walls across the tanked zones, in the number of coats or the sheet arrangement the system sets, with each stage allowed to do what it needs before the next. Corners, floor-to-wall junctions and movement joints get the system's own reinforcing tape and preformed pieces, bonded in rather than laid on top. Penetrations for the waste, the valve, the rail and the screen fixings are made once, in the right place, and sealed with the collars the system provides. The drain flange is bonded into the membrane so that the two are continuous - that connection is the single most common leak path in a wet room and the one most often rushed.

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   Step 5: Detail the threshold and the level access

   The threshold is where the two requirements of the room meet. Level access means no upstand at the door, so the containment has to come from the falls and from a tanked perimeter that turns up behind the surrounding construction rather than from a step. The membrane is carried out past the door line and closed against the adjoining floor construction to the designer detail, and the finished floor level inside and outside is checked so that nothing trips. Where a screen or half-height panel is used, its fixings penetrate the tanking and are sealed as penetrations, not driven through and forgotten.

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   Step 6: Test the waterproofing before a single tile

   The room is tested while the membrane is still visible. The drain is temporarily plugged and the floor flooded, or the test the system specifies is carried out, and the water is held and watched - with the ceiling and the rooms below inspected as well as the wet room itself. Any repair is made to the membrane and re-tested. This is the last moment at which a fault is cheap: after this, every defect costs the tiling, the ware and the ceiling below. On most projects the test is witnessed and photographed, because it is the evidence that matters if the room ever leaks.

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   Step 7: Tile over the tanking without damaging it

   Tiling goes on with adhesive and grout compatible with the membrane, using tiles and a format the falls can accommodate - large rigid formats do not follow a fall towards a centre gully, and mosaic or smaller formats are commonly used in the falling area for that reason and for slip resistance underfoot. Nothing is fixed through the tanking that was not already sealed, and no trade is allowed to drill the floor afterwards. Movement joints in the substrate are carried through the finish. Tile edges around the drain are cut to sit level with the grating so that water leaves rather than pools at the edge.

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   Step 8: Seal, commission and prove the drainage in use

   Sanitary sealant closes the junctions between finishes after tiling and grouting, tooled continuous. The room is then run in service: the shower on for a sustained period with the floor watched for standing water, the trap checked for its seal, the grating lifted to prove the access for cleaning, and the surrounding floor and the ceiling below inspected again. The maintenance access to the trap is demonstrated at handover, because a wet room drain that cannot be cleaned will be blocked within a year and will then be tested by somebody else.