What a concealed mixer consists of
A concealed mixer has two parts: a hidden body inside the wall (with a thermostatic cartridge, isolating valves and a diverter) and an outer trim with handles, fitted after tiling. The wall also carries pipes to the rain head and the hand shower.
Outside you see only the trim, and all the mechanics are hidden. That gives a clean wall with no protruding parts, but moves the risk inside: if the body is set wrongly or with an error, correcting it means lifting the tile.
So the decision is made before the walls start: which thermostat, how many outlets (rain head, hand shower, body jets), how they switch, where the isolating valves are.
Is the pressure enough for a rain shower in an old building?
In an old building pressure is often low, especially on upper floors, and for a large rain head it must be checked before ordering. As a guide, a 300 to 400 mm head gives a comfortable spray at a dynamic pressure from 2 bar, and the flow of such heads is typically 15 to 25 l/min according to the data sheet.
Pressure is measured with a gauge at the future shower position with the tap open: static pressure with the tap closed says little. Flow is checked with a bucket and a stopwatch. Hot and cold should be close in pressure: a thermostat works badly if one supply is weaker than the other.
If the pressure is not enough, there are fixes: a booster pump for the flat, a smaller head with good atomisation, a low-pressure version, or a building-level solution through the comunidad. Hot water is also a question: a 20 l/min head mixed to 38 °C needs on the order of 30 kW of instantaneous power if the water is heated from 15 to 55 °C. That is why a storage cylinder is usually needed.
Is a thermostat necessary?
Not obligatory, but for a rain head and an expensive shower you want one. A thermostat holds the set temperature through pressure swings: if someone opens a tap in the kitchen, the shower water does not suddenly turn icy or scalding.
Another advantage is safety: thermostats have a 38 °C stop that requires pressing a button for hotter water. For children and older people that matters a great deal.
A thermostat is sensitive to limescale. Barcelona's water is hard, and the cartridge is best protected by a filter ahead of the mixer. We write about hard water and filtration in a separate article.
How do you maintain a concealed mixer?
The thermostatic cartridge is replaced from the front: you remove the trim and handles, take out the cartridge, and the wall stays intact. That is the norm on serious ranges. Strainers and check valves come out the same way.
It is worse if the body or a pipe itself fails. Then you need access from behind: an inspection hatch in the neighbouring room, a service cupboard or a removable panel planned in advance. Without such access, a repair means lifting the tiling.
Plan isolating valves separately too: at the bathroom feed and on the riser, so that you can shut off the water without leaving the whole flat dry. What to check before closing walls is covered in our article on services.
In what order is it installed, and why can't you change the brand?
The order is this. First you choose the whole range: mixer, rain head, hand shower, diverter. Then the body is fixed to a rigid frame in the wall, using the maker's template, at the correct depth allowing for tile and adhesive thickness. Then the pipes are run, pressure-tested, and the wall around the body is waterproofed. Only then is the tile laid and the trim fitted.
The brand cannot be changed after closing for a simple reason: the body and trim of one series are designed together, with depth, centres and cartridge seating. A trim from another maker will not fit or will leave a gap.
There are universal bodies that fit several series from one manufacturer. But to change manufacturer you must replace the body, which means opening the wall. If after the order the contractor suggests an "equivalent", that is a reason to stop: we deal with substitutions in our article on material substitution review.
Rain head: ceiling or wall?
A ceiling head looks cleaner and falls straight down, but needs a pipe in the ceiling and false-ceiling depth. For a 300 to 400 mm head you need about 10 to 15 cm above the ceiling for the connection. A wall head on an arm is simpler and needs no access from above.
The flow of a rain head loads the drain: 20 l/min is about 0.33 l/s, and a typical linear drain takes 0.5 to 0.8 l/s on its data sheet. The margin is small, so the drain is chosen by flow, not by looks.
If several body jets and the rain head run together in the shower, the total flow rises, and pressure, drain and water heating are calculated for peak load. This is where an engineer's experience helps.
How to plan it, and what we do
Planning goes like this: choose the range and calculate pressure and flow, draw the supply scheme, fix the body position on the wall plan, plan access for maintenance, waterproofing and pressure test. All of it is recorded on a drawing before the wall is closed.
At BCN YARD we prepare a decision sheet: models of mixer, rain head, shower, drain and the water scheme. The body is fitted before tiling, pressure-tested and checked, and the trim goes on at the end, after the final finishes.
If you want a concealed thermostat and a rain shower, we visit, measure pressure and flow in your flat and tell you what can be fitted and what will need a pump or a cylinder. The price is calculated in the estimate after the visit and measurements.
Frequently asked questions
Is the pressure enough for a rain shower in an old building?
Not always. A 300 to 400 mm head usually wants 2 bar of dynamic pressure and 15 to 25 l/min on the data sheet. Pressure is measured with a gauge with the tap open, flow with a bucket and stopwatch. If it is short, fit a booster pump, a smaller head, or go through the comunidad. Hot water also needs reserve: expect to need a cylinder.
How do you maintain a concealed mixer?
The thermostatic cartridge is replaced from the front: remove the trim and handles and the wall stays intact. If the body or a pipe fails, you need access from behind: a hatch in the next room, a service cupboard or a removable panel planned in advance. Isolating valves go in an accessible spot and a limescale filter ahead of the mixer.
Is a thermostat necessary?
Not obligatory, but worth having for a rain head and an expensive shower. It holds the set temperature through pressure swings and stops the water going icy or scalding when someone opens a kitchen tap. The 38 °C stop protects children and older people. Barcelona's water is hard, so a limescale filter is needed.
Can you replace a concealed mixer without lifting the tile?
The thermostatic cartridge, yes, from the front. The body or a pipe only if rear access was planned beforehand. You cannot change manufacturer after closing: body and trim of one series are designed together. The range is chosen before the walls start.