Shower tray or floor is sinking - what could be the cause?

I would completely modernize the bathroom as it looks (I am really shocked) and not leave a single stone unturned. I think if you do a lot yourself, it could be done for under 10,000.

Everything out and new!

First, open the floor next to the shower tray in one spot to check the existing structure. Then you will have to live with a hole in the floor for a while, but you can have the structural engineer take a look and you don’t need a crystal ball to plan the new floor structure correctly.

Cleaning would already help... Sorry, but I would never post photos of tiles with 3 mm of dirt stuck on them. Just looking at it gives me herpes!

You mean the white "wall tiles"? Those aren't tiles, but adhesive foil that is peeling off... that was done back then to cover up the ugly color the previous owner had smeared on the tiles. But of course it looks totally bad by now and obviously needs to be redone.

But on the topic:

We removed the PVC covering in front of the shower and the tiles underneath. Unfortunately, no real cause for the sinking of the floor can be seen.
(see photos)





The building is from 1905, I unfortunately don't know when the attic was converted. Getting a structural engineer involved would probably not be cheap; I'd rather avoid that.

My hope is still to simply level the floor with flow filler and retile...

I would bet that the "sealing" (meaning the silicone) around the tub has not been functioning for quite some time and water has happily flowed under the shower tray. Old building from 1905 and DG then means with almost absolute certainty a wooden beam ceiling and it or its cladding (floorboards, chipboard, etc.) will have rotted away. Consequence: The shower tray will sink and sooner or later end up in the floor below – with some "luck" there is a beam in that spot that might hold out a bit longer. You won't get around a structural engineer and in the interest of your health, you shouldn't even try. Remove the tile adhesive/screed under the already removed tiles, then you will see more, or open the cladding of the shower tray so you can look underneath.

You mean the white "wall tiles"? Those are not tiles, but adhesive foil that is peeling off... it was done back then to cover up the ugly color the previous owner smeared on the tiles. But of course it looks totally awful by now and naturally needs to be redone.

No, I mean the thick dirt that sticks in the corners at the bottom!!! That is really disgusting...

I just looked at it again, it's really filthy. I would be extremely uncomfortable publishing such photos...