Wet Room Falls Set to 1 in 50 with an Impey Aqua-Dec Linear Former

A pre-formed shower deck fixes the fall before the adhesive bag is opened. In the Impey Aqua-Dec Linear range, the gradient is pressed into a rigid board that sits flush with a chipboard or plywood subfloor, so the finished tiled surface reaches roughly 1 in 50 without hand-screeding. Impey quotes a maximum tile size of 600mm by 600mm on the standard Linear deck, with a linear waste channel along one edge.

That layout affects the tiling as much as the drainage. A centre gully asks the tiler to form four planes into a pyramid. An edge channel lets the floor pitch in one direction, so large-format tile can sit flatter and cleaner across the shower area.

The 1 in 50 figure comes from the point where most UK tiling guidance and deck manufacturers meet for tiled shower areas. It is shallow enough to feel close to level underfoot and steep enough to move water toward the outlet before surface tension holds it in the grout joints. On a 1200mm deck, that fall gives a 24mm difference between the high edge and the channel. Reproducing that by eye in wet screed is how a small puddle appears two weeks after handover.

What the pre-formed fall removes

Standing water in a finished wet room usually traces to one of three faults: the fall reverses somewhere across the floor, a tile sits proud of its neighbour and creates a lip, or the channel is set too high against the surrounding tile. The Aqua-Dec deck deals directly with the first fault because the board leaves the factory with the slope moulded into it.

There is no wet mix to slump while it cures. There is also no long straightedge session trying to hold a consistent 20mm per metre across an awkward corner. The installer is bonding tile to a surface already pitched toward the waste.

The remaining two faults still sit with the tiler. A 600mm porcelain slab can still finish with a 2mm lip at the channel end, and that lip can hold water even when the deck underneath is falling correctly.

Levelling clips earn their keep on that part of the job. Systems such as Rubi Tile Level or Raimondi RLS pull neighbouring tiles into the same plane while the adhesive cures, keeping the channel-side edges aligned. On a sloped deck, gravity tries to slide the upper tile downhill into the joint before the adhesive grabs, so back-buttering and a firm first press carry more weight than they would on a flat floor.

Tile thickness also meets the deck fall at the channel. If a waste grate is designed to finish level with a 10mm tile plus 3mm of adhesive, a switch to a 20mm slab leaves the grate recessed and water sheets past the opening. Impey publishes the finished-floor build-up for each grate height, and matching the tile and adhesive bed to that figure keeps the drainage plane continuous.

Bonding to the deck and tanking the joints

The deck becomes part of a waterproof shower floor only when the surrounding surface is tanked and the tanking runs continuously into the channel flange. Impey supplies its own waterproofing kit, and the Aqua-Dec flange sits under the tanking membrane. Water that passes through a grout joint then travels across the membrane and into the channel, with the subfloor kept outside the drainage path.

The waterproofing role belongs to the membrane layer. The adhesive bed provides the bond between tile and deck, while the tanking system controls the water path below the tile surface.

For the tiling itself, a flexible S1-rated cement-based adhesive is the sensible choice on a board exposed to thermal movement and foot deflection. Mapei Keraflex Maxi S1 and BAL Rapid-Flex One both give enough deformability to cope with the slight flex of a floating deck without shearing the bond.

The trowel follows the tile. A 6mm notch suits mosaic, while 10mm to 12mm is typical under 600mm porcelain. Full coverage still has to be checked by lifting a tile early in the run. Voids under a shower-floor tile hold water, and efflorescence later blooms through the joints from those damp pockets.

On walls feeding into the deck, a separate uncoupling and waterproofing layer is common. Schluter Ditra matting and the Ditra sealing system are frequently specified where the wall build-up needs decoupling and a bonded waterproof plane, and the Kerdi membrane handles the vertical tanking.

An uncoupling membrane on adjacent floors breaks the stress path between a moving subfloor and a rigid tile, so cracks in the substrate do not telegraph into the grout. The Aqua-Dec deck itself does not need Ditra over it because the deck is already the substrate.

Cutting 600mm porcelain to the channel line

The cut along the channel is the one that can ruin the look of a wet-room floor. A 600mm porcelain slab needs to meet the linear waste with a clean, straight edge, because a ragged score looks unfinished and leaves a chip that traps grime.

Grout and the efflorescence that follows

Epoxy grout is the honest answer for a shower floor, and its stain-resistance claims hold up better than most marketing in the tile trade. A two-part epoxy such as Mapei Kerapoxy or Litokol Starlike cures to a dense, non-porous joint that does not absorb the soap, limescale and body oils that can discolour cement grout within a season. It also avoids efflorescence because there is no free lime to migrate.

The trade-off is real. Epoxy is stickier to work, sets on a shorter clock, and needs a diligent wash-off with the right pads. Miss that window on matt porcelain and the haze can take an evening of scrubbing.

Cement grout in a wet room brings efflorescence sooner or later. Water moving through the joint carries dissolved calcium hydroxide to the surface, where it reacts with air and leaves a white crystalline crust along the grout lines. The staining is usually worst near the channel because that part of the floor stays damp longest.

Lithofin efflorescence remover is the standard corrective. It is a dilute acid wash that dissolves the deposit without etching the porcelain, applied after the surface has been wetted so the acid does not draw into the joint and restart the cycle. Acid washing gives only temporary relief if water continues to sit in a porous joint, the condition that correct 1 in 50 fall and full adhesive coverage are meant to reduce.

When porcelain crockery and a matt-finish tile are involved, test the grout colour on an offcut first. Dark epoxy on a pale, textured porcelain can leave a permanent shadow in the surface texture if the wash-off is late, and efflorescence remover cannot fix a grout stain because there is nothing crystalline to dissolve.

A worked build-up for a 1200 x 900 deck

Take an Impey Aqua-Dec Linear at 1200mm by 900mm, with the channel along the 900mm edge. The fall runs across the 1200mm dimension at 1 in 50, giving roughly 24mm of drop from the high wall to the channel. The tile is 600mm by 300mm porcelain plank, 10mm thick, with the long edge running downhill so the joints follow the fall.

A 10mm notched trowel with Keraflex Maxi S1 lays a bed that compresses to around 4mm to 5mm under the tile. Finished floor height at the high edge is therefore the 10mm tile, roughly 4mm of adhesive, and the deck thickness above the subfloor. Impey’s grate for a 14mm finished build-up is the one to order so the grate top sits flush with the tile at the channel.

Levelling clips at 300mm centres along each plank keep the downhill edges in plane. Where two planks meet the channel, their cut edges need easing, and the grate should sit a whisker below the tile face. A proud grate deflects water before it reaches the opening.

Grout the field in epoxy, wash off inside the manufacturer’s stated window, and check the fall with a spirit level laid across the tiles toward the channel before the adhesive fully cures. If the bubble shows any reverse pitch at the wall end, the tile there is sitting proud and belongs out of the bed while the adhesive is still green. Does the bubble read the tile face and the grate lip as one uninterrupted fall?