Shower bar thermostat fitting

Is it normal practice to fit a shower bar type thermostat to the tiles but sticking with mastik. I know there are special nrackets available but out builder reckons sticking it is normal.

The reason I ask is that our thermostat has come loose and the plumber has just returned to stick it up again. I caught sight of the pipes inside the wall and they are not screwed down at all. He reckoned that this was the standard thing to do.

Also the thermostat drips like mad when switched off. The plumber reckoned the "cartridge" could be changed but it would probably go again. His suggestion was to change the whole thermostat for around £100 - the shower is less than 3 years old !!!!

The cheaper bar type showers often did not have any fixing brackets/points to fix to the wall. You were relying on the pipe work in the wall to hold them in place and the silicone seal that makes the shower/wall water proof.

So is it normal practice to stick them on?

The valve has two chrome cone shaped parts covering the pipes and these are the only bit that actually touches the tiles. So the mastik has to grip a thin circle of metal.

The builders plumber has now restuck the valve to the wall but I am concerned that it will come away again.

It also seems very difficult to add a bracket afterwards as this involves removing the tiles (unless someone has a better idea).

Any information gratefully received.

These are ideal.
They are fixed on the surface which makes them even better.

They look like the bits I need. Does anyone know how they are fixed to the tiles?