Installation and Bedding of a Shower Channel

Every channel is a little different, so the plumber always follows the manufacturer's fitting instructions. The basic sequence is similar for most products:

1. Check the waste pipe: it must be clear and clean, and its position and fall must allow a connection.
2. Clean and level the base. It must be solid, with no cracks or hollows.
3. Lay edge insulation strips along the walls so the screed does not press against them.
4. Set the channel on its adjustable feet or brackets. Adjust the height so the top edge will sit flush with the finished tiles, and check it with a spirit level both lengthways and across.
5. Connect the channel outlet to the drainage, usually with plastic push-fit waste pipe. The joint should be watertight but slightly flexible.
6. Pour water into the channel and watch whether it drains smoothly and whether the joint drips.
7. Tape over the channel so no screed gets inside, then bed it in gradually. Spread the mix evenly so it does not push the channel out of position.
8. Screed the floor to a fall towards the channel and leave it to cure.

Why so many checks before the screed goes down? Because anything under the screed can only be repaired by breaking it out again. A few minutes with a spirit level and a bucket of water saves a lot of trouble later.

Shower channels are made of plastic or stainless steel. A plastic body is light and perfectly adequate for an ordinary home shower. Stainless steel channels are tougher and are chosen where the shower gets heavy use or where a more robust solution is needed.

The outlet type and the build-up height matter more than the material:

• Horizontal outlet leaves from the side and connects to a pipe running inside the floor. It is the usual choice, but it needs enough floor depth.
• Vertical outlet goes straight down, for example through the ceiling below or into a prepared pipe. It is used when there is no room in the floor for a horizontal run.
• Low-profile channels have a smaller build-up height and help in renovations where the floor cannot be raised much.

Most channels are placed along a wall. The floor then falls in one direction only, the tiles are easier to cut and the water drains evenly. Good floor drains have a trap that stops sewer smells and are made to EN 1253. It is worth checking this in the product data sheet.

In a new build the job is simpler. The screed height is planned in advance, the waste pipe runs exactly where it should and the fall is formed when the screed is laid. In a renovation it often turns out that the old floor is too shallow or the waste pipe is in the wrong place. Then a chase has to be cut, the pipe moved, or the whole floor raised.

The work gets more involved, and therefore more extensive, mainly with:

• a shallow floor that needs a low-profile channel or chasing out,
• moving or extending the waste pipe,
• an uneven or cracked base that has to be repaired first,
• underfloor heating, which has to be coordinated with the channel position and screed thickness,
• poor access, for example an upstairs flat with no lift.

In a block of flats, check before you start where the shared soil stack runs and whether any work on it needs approval from the building management or owners' association. If load-bearing parts would change or the floor slab would be cut extensively, speak to your local building authority. Whether you need to notify them or follow another procedure depends on the scope of the work and your local building regulations, so always check directly.

Bedding the channel in does not make the shower watertight on its own. Cement screed lets water through, so a flexible liquid waterproofing membrane is applied to the cured base, usually in two coats. Sealing tapes go into the first coat: in the corners, along the joint between wall and floor and around the channel. Many channels come with a factory-fitted sealing collar that is embedded directly into the membrane.

The riskiest spots are the joint between the channel and the membrane and the corner where the channel meets the wall. A leak there often shows only months later, for example as a damp patch on the wall of the next room or on the neighbour's ceiling below.

Once the membrane has dried according to the manufacturer's instructions, the shower area is flooded with water and left to stand. Tiling only starts when it is clear that no water escapes anywhere. Watch the timing with the screed too: cement screed usually needs several days before you can walk on it, and longer before it can be waterproofed and tiled. The mix manufacturer gives the exact times. While curing, the screed should be protected from draughts and direct sunlight.

• Wrong fall. A fall of roughly 1.5 to 2 % towards the channel is usual. With less, water sits in the corners; with an uneven fall, it runs out of the shower.
• Channel knocked out of position. If it is not well supported, the screed lifts or tilts it as it is laid. The grate then does not sit flush with the tiles.
• Too little screed over the pipe. The pipe should be covered by enough screed, usually around 4 cm, otherwise cracks are likely.
• Rigid or leaking waste joint. This causes smells and water under the screed.
• Missing tapes or a single thin coat of membrane. Cutting corners on waterproofing is the costliest saving, because fixing it means taking the tiles up.
• Tiling without a water test. The fault is then only found once the bathroom is finished.

It pays to go through these points before tiling and again at the end:

• The top edge of the channel is level and at the height of the finished tiles
• The channel does not move when pressed and there are no hollows around it
• Poured water drains smoothly and no puddles remain in the shower area
• The waste joint was tested before bedding in and did not drip
• The screed around the channel has no cracks
• The waterproofing has two coats, with tapes in the corners and around the channel
• The flood test was done before tiling
• The trap is in place and there is no drain smell from the outlet
• The grate and trap insert can be removed for cleaning
• You have the fitting instructions and data sheet for the channel in case of a warranty claim