ᐅ Floor construction on a timber joist ceiling?

Hello everyone,

We have purchased a house from the 1950s and are currently renovating/restoring it.

We plan to create a bathroom on the upper floor. The existing floor covering was a wooden plank floor nailed to the wooden joists. We have removed the planks, and it currently looks like in the pictures. We would like to have a tiled floor.

My question is: How can we prepare the floor so that tiles can be laid on it? The tiler mentioned something about styrofoam beads mixed with concrete/cement. He said this would be lightweight and suitable for tiling. He did not recommend OSB boards.

Can you provide some advice on this?

Thank you in advance.

Best regards,
Daniel

Before you can put lightweight concrete/lightweight screed/dry screed or something similar on top, you first need a load-bearing layer – for example, floorboards again. You must not load the "filling" in the middle, otherwise the ceiling on the ground floor will collapse. I would then use dry screed panels with a lightweight aggregate.

Did I understand the structure correctly (from top to bottom)?

Tiles
Dry screed boards
Filling layer
Floorboards
Wooden beams

Yes, that’s one way to do it.
For the bathroom, a waterproof membrane should be installed beneath the tiles.

Why install floorboards over the joists again? Often, dry screed panels are laid directly. Am I missing something?

If the beams are level (which is often not the case in existing buildings) and load-bearing boards are used, the floorboards would not be necessary.