Installation and Recessing of Concealed Cisterns/Frames

People mean different things by a concealed unit. Usually it is one of these:

• The body of a concealed shower or bath valve
• The body of a wall-mounted basin mixer
• A concealed toilet frame, which is a steel frame with a built-in cistern

The process is similar for all of them. What changes is the size of the unit and how much wall has to come out.

For a valve you only need a recess for the body and chases for the hot and cold supply. A toilet frame in a masonry wall often means opening up a larger area. Alternatively, the frame can stand in front of the wall and be boxed in with plasterboard. In a stud partition nothing is chased out at all: the unit is screwed to the metal studs or to a mounting board.

If the flush plate has lighting or electronic operation, the electrical supply to it is a job for a qualified electrician, not the plumber.

Marking out

The first step is to mark the centre line, the height and the position of the supply pipes, following the manufacturer's installation instructions. A shower valve is usually set roughly 100 to 120 cm above the floor. The exact height depends on how tall the people in the household are and whether there is also an overhead shower. On a toilet frame, the pan and flush plate heights are set using the markings on the frame. A good tradesperson also thinks about the tile layout at this stage, so the controls do not end up awkwardly on a grout line or the edge of a tile.

Cutting the recess and chases

Pipe chases are cut with a wall chaser connected to a dust extractor. The recess for the body is cut with a core drill or a combination hammer. The depth depends on the unit and is usually roughly 7 to 12 cm. Chases should run straight up or straight across, never diagonally. That way anyone working on the wall later can guess where the pipes are.

Setting the correct depth

This is the most important step. Most units have minimum and maximum depth marks on their plastic protective cover. These marks refer to the finished wall surface, including tile adhesive and tiles. So the unit is set to the future tiled surface, not to the bare masonry. It also has to be level and plumb. Otherwise the cover plate or flush plate will sit crooked.

Fixing and connecting

The unit is first fixed mechanically to the wall with screws or brackets. Then it is bedded in with mortar or a gypsum-based filler. Expanding foam on its own is not enough. Turning the lever and pressure surges in the pipes can work the unit loose over time. After that, the supply pipes are connected. These may be multilayer, PPR or copper, depending on the system in your home.

Pressure test and sealing

Before the wall is closed up, the pipework is pressure tested according to the pipe manufacturer's instructions. Only when every joint holds is the wall made good. In the wet area around a shower, waterproofing follows next, with special sealing collars around the outlets so water cannot get behind the tiles.

The type of wall has the biggest effect on how long the job takes, and therefore on what it costs.

• Aerated concrete blocks and plasterboard are the easiest. They cut quickly and cleanly
• Clay brick is common. With hollow bricks the recess has to be filled well so the unit holds firm
• Concrete and precast concrete panels are the hardest. Cutting is slow, noisy and dusty, and you often hit reinforcement
• Old mixed walls made of brick, concrete and patch repairs bring surprises, and the unit is harder to anchor

The work also takes longer if the water supply is far away, if pipes have to pass through another room, if old pipework has to be replaced first, or if the valve has several outlets. It helps if the bathroom is already stripped back to bare masonry and you have chosen both the exact valve model and the tiles.

In blocks of flats, especially concrete panel buildings, the walls around the bathroom are often load-bearing. You cannot cut into a load-bearing wall however you like. Horizontal chases and larger openings in particular can weaken the structure. Before any work starts, contact the building management or the owners' association and find out which rules apply in your building.

Work on load-bearing walls usually falls under local building regulations. Check with your local building authority whether you need to notify them or follow another procedure. For larger openings in a structural wall, a structural engineer usually has to assess the work first. A common solution avoids the problem altogether: a plasterboard service wall is built in front of the existing wall, and the unit goes into that without touching the structure.

• Wrong depth: set too deep, the extension piece may not reach. Set too shallow, the cover plate stands proud of the tiles
• Not level: the lever or flush plate sits crooked, and fixing it means breaking out tiles
• No pressure test: a leaking joint shows up as a damp patch on the wall or in the neighbour's flat
• Fixed with foam only: the unit shifts over time and damages the seals or the tiling
• No waterproofing around the outlets: water gets behind the tiles and the masonry stays damp
• Instructions thrown away: spare parts are hard to find when the cartridge needs servicing or replacing

In practice it often happens that the customer chooses tiles only after the unit is already in. If those tiles, together with the adhesive, are thicker or thinner than planned, the unit no longer sits right. It pays to choose your tiles beforehand.

Before the wall is closed and tiled, go through these points with your tradesperson:

• The unit is firmly fixed and does not move when you push it
• It is level and plumb, and the centre line matches the marking
• The depth matches the marks on the cover for the planned tiles
• Hot and cold water are connected to the correct sides
• The pressure test has been done and all joints are dry
• The protective cover is still on, so no mortar gets inside
• Sealing collars are fitted around the outlets in the wet area
• You have photos of the wall showing the pipe runs before it was closed
• The installation instructions and documents for the unit are kept for future servicing