Extension of the screed opening. Can this screed break?

First of all, many thanks for the support in presenting what I actually want to know. I probably would not have been able to convey sufficiently well on my own what I actually want.

Now to the situation:

The concrete floor slab is directly in the ground, no basement. Insulation material is installed on it; according to the site manager, it is polystyrene.

I found the following photo as a supplement:



Different thicknesses of calcium sulfate screed were laid on this construction. In the area of the cutout about 85mm, in the living area about 60mm.

The fireplace cutout was separated from the living area with blue insulation strips:


Overall, it looked like this:


To me, it appeared "professional" up to this point.

Subsequently, next to the original cutout, another strip was cut out of the living area and connected with the fireplace cutout. Apparently, different material was inserted there, a gray strip. Between the gray strip and the fireplace cutout there is no blue insulation strip, since this is supposed to be the new fireplace area. Between the gray strip and the living area, however, there is again an insulation strip:



I hope I was able to answer all questions sufficiently and thank you for your patience.

OK. So the joint is present.

Whether PS insulation is problematic, I think only KlaRa can answer that. Is the thickness of this insulation layer known?

The exact thickness of the insulation layer is not known to me. Based on pictures, I estimate that it will be about 20cm thick. Admittedly, however, it is very difficult to estimate based on pictures.

Hello "Seol". The first photo you attached is meaningful to me. Your current information is also helpful, as it now paints a comprehensive picture of the construction. The ground-contacting floor slab was apparently sealed at the top. Nothing unusual, but this naturally means that a composite structure, as I had proposed, is no longer possible. In the case of a basement, which I had assumed, this sealing layer would not have been present. Picture 1 shows that the recess in the insulation layer was made for the chimney/wood stove, meaning: the chimney does not stand on the insulation layer. That would not have worked! That the calcium sulfate screed was "patched" with a cementitious material, well, that's just the way it is. This can be accepted, no disadvantages arise from it. The black pipe in photo 1, I wonder, going towards the chimney, what function does it serve? Ultimately, however, as executed, there will very likely be no problems. The movement joints were installed leading to the floating screed. So nothing suggests that future enjoyment of the chimney will be hindered by structural issues or uncertainties in the construction. ------------------------------- I am now signing off from this topic, enjoy your new home: KlaRa

Hello KlaRa,

thank you for your feedback. That reassures me.

The "pipe" which you see in the first picture is the condensate drain.

Best regards,
Sebastian

The exact thickness of the insulation layer is not known to me.

It should actually be visible in the design plans (thickness and type of insulation, actually the entire construction of the floor). Of course, only the planning, not the execution.