Bathroom after complete renovation high humidity

Hello,

we have completely renovated a house and are generally satisfied. However, we have noticed that our bathroom on the ground floor has a high humidity level. My smart radiator thermostat shows about 70%. The other rooms are not affected.

The bathroom has a shower, and the window is opened while showering. Even after 24 hours, moisture is still noticeable in the bathroom. There is also a slight chemical smell that I unfortunately cannot identify.

Nothing can be seen on the tiles or the window.
The following was done, which should have been in June/July:
- Walls opened, pipes re-laid, walls closed and plastered
- Floor removed, new screed applied
- Window in the outer wall replaced, smaller window, therefore bricked up and plastered
- Newly tiled

Does anyone have an idea how I can best proceed to find the cause here?
Thank you very much in advance!

The answers are always the same:

what is the relative humidity if you haven't showered for about a week?

Get a capacitive moisture meter and check walls/floors.
Maybe there is a leak in a pipe in the wall?!

Hello, first of all thank you very much for your help. The ideas are very good and we will try them. So I would not shower in this bathroom for a week, of course still ventilate accordingly, and then see if the humidity rises again. I will also get myself a moisture meter. I really hope that we don't have a leak...

If the problem exists only in the bathroom, that also rather suggests a local cause. Checking the walls is certainly the right thing to do. But just to be sure:

[*]The list of tasks refers to the entire house, not just the bathroom, correct?
[*]Which screed was used? Cement, anhydrite, calcium sulfate, something else? With/without drying accelerators?
[*]Thickness of the screed layer?
[*]Was underfloor heating installed and was the screed heated?
[*]What measures did you take to dry after plastering and laying the screed?
[*]How much time did you allow the screed to dry before tiling?