Bathroom renovation, bathtub directly on insulation?

I would not completely omit the screed under the tub. Even if the insulation supports the weight, otherwise you lack a stable base – over time, something can settle or put strain on the drain. If you want to set the tub deeper, simply make the screed thinner at that spot or use a firmer insulation. Some also place a construction panel underneath, which works well.

Thank you for the note. How can it be clarified how much/little screed should be placed under the tub? Alternatively, a construction board on the insulation instead of screed? That initially sounds like a simple option. Same as with the screed, how do I determine a sufficient thickness for the construction board? Since these usually only have a 60 cm dimension, at least 2 boards will have to be placed under the 180x80 tub.

This is how you can do it – the important thing is that the tub rests fully and stably. XPS alone does not reliably support that. Construction boards are possible, but only with a pressure-distributing layer, otherwise there will be movement and problems at the drain. Separate the transition to the screed cleanly, otherwise it will crack there. It is better to use two glued 20 mm boards with full support.

So you mean 2 layers of 20mm construction board each as an underlayer laid on top of each other rotated by 90 degrees? And then a separation layer like, for example, an edge insulation strip between that and the screed? Sounds like a potential problem area anyway with your restrictions. Leave out screed at the bathtub area and then pour an additional 5cm of screed there afterwards as a safer alternative?

With the combination of Rotband Pro and Grigolin, you already have a pretty dense surface, almost like painter's fleece. Brush-on or roller-applied plaster is technically possible, but check the absorbency beforehand – does the water bead off or soak in? This is crucial for adhesion behavior. Your plasterer is right: 0.5 mm grain size is hard to apply cleanly by hand because it sets too quickly. 1 mm is a good compromise. Alternatively, a fine lime plaster (approx. 0.8 mm) also works – matte, sturdy, and with a natural appearance. It only becomes easy to maintain and child-friendly through the final coating: preferably silicate paint or durable dispersion paint instead of simple "plaster paint" from the hardware store.

With the combination of Rotband Pro and Grigolin, you already have a pretty dense surface, almost like painter's fleece. Brush or roller plaster is technically possible, but check the absorbency beforehand – does water bead off or soak in? That is crucial for the adhesion behavior. Your plasterer is right: 0.5 mm grain size is hard to apply cleanly by hand because it sets too quickly. 1 mm is a good compromise. Alternatively, a fine lime plaster (approx. 0.8 mm) also works – matte, robust, and with a natural appearance. It only becomes easy to maintain and child-friendly with the final coating: best is silicate paint or durable dispersion paint instead of simple "plaster paint" from the hardware store.

Wrong topic ;-)
This is about a bathtub...