Professional sealing of holes in the wall

Dear forum,

I am inexperienced in construction and do not know if the following procedure by our general contractor is correct: My wife and I are currently building our single-family house with a GC. The walls are made of expanded clay. Due to a communication error, our construction company made a wall (inside of the exterior wall) with several holes. Depth approx. 8 cm, diameter approx. 6 cm. Tilt switches were supposed to go there, but it was the wrong spot. Now the holes have been closed again by filling them with Styrofoam panels and then plastering over them. I noticed this (the spots were no longer visible) when I tapped the areas with my fingers and they sounded hollow in the respective places. From tapping, I actually knocked a small hole in one of the spots. The site manager said that the contracted craftsmen were supposed to do it this way and that the surface could only be pressed in because the plaster was not yet dry. The craftsmen were there about 3 or 4 days ago.

As a layperson, I cannot imagine that such a procedure complies with the recognized rules of technology. A solid wall made of expanded clay is patched with Styrofoam panels which are then plastered? These spots will be a weak point forever. If I lean heavily on the wall with my elbow once, will I have a hole in it? Shouldn’t it be filled with something hard like mortar or similar?

Are the 150+ holes for sockets, light switches, roller shutter buttons completely filled with mortar after the electrical work is connected? With a decentralized ventilation system or an exhaust hood, you even have a 150mm thick hole in the outer wall.

Expanded clay is basically an insulating brick. To apply mortar to it now... If I ever get fed up with my fans, I'll stuff Styrofoam in there and definitely not seal the entire hole in the wall with mortar. That would be a perfect thermal bridge.

For an ETICS, for example, no mortar is allowed in the joints between the insulation boards because that would create a thermal bridge.

Hmm, I don't understand why no lightweight masonry mortar (LM21) or Tiroplan slot plaster was used there. Presumably, the general contractor used XPS. I don't believe they actually put EPS in there?! Is there a photo of the spot?

Hmm, I don't understand why no lightweight masonry mortar (LM21) or Tiroplan slot plaster was used. Presumably, the general contractor used XPS. I don't believe they actually inserted EPS in there?! Is there a photo of the spot?

I seem to remember that the word Styrofoam was actually mentioned. In any case, neither XPS nor EPS. Luckily, we have a photo: [ATTACH alt="Foto.jpg"]84562[/ATTACH]

The fragments actually look more like EPS ("Styrofoam") than XPS. They look about the thickness of the impact sound insulation under the screed. I am not an expert to judge whether the general contractor "is allowed" to do this, but as the client, I would not accept it with the reasoning of the significantly lower load-bearing capacity in case something is ever mounted on this wall, coincidentally at this spot. Just kindly ask him to fill it with a building material that at least approximately has the strength properties of your expanded clay, done. Whether he does it with slot plaster or lightweight masonry mortar doesn’t matter, definitely better than Styrofoam.

Thank you both for your answers. xMisterDx mentioned the point of the thermal bridge when using mortar. Is this not the case with the variants you suggested (Leichtmauermörtel LM21 or Schlitzputz)? Google does output that LM21 Leichtmauermörtel is very highly thermally insulating.