Hello everyone,
thank you very much for your contributions.
Well, I have made some progress by now...
-The company I commissioned has an impeccable reputation, and offers for prefabricated houses are not easily made.
-I googled the silver foil, and the material also sounds reliable in terms of quality. Below are the properties of the product:
Advance offers a wide range of foil adhesive tapes with acrylic adhesives that increase their adhesion over time and, conversely, can be removed if left on only for a short time.
Our tapes were developed for various applications and guarantee additional performance and resistance to extreme temperatures.
Advantages:
• Provide excellent adaptability
• Are water-repellent and offer a complete vapor barrier
• All foil tapes from Advance have a white siliconized release liner and are very easy to unwind
• All tapes from Advance are fully tempered and as soft as the production processes allow
• All adhesive tapes are easy to tear.
...
I can well understand that hardly anyone wants to penetrate the wall structure with a thick ETICS. We had to make some penetrations of the exterior wall ourselves during the shell construction (e.g., for the controlled residential ventilation on the outside of the wall high up in the first insulation layer). For this, we had to put in a huge effort with separate boxes made of screen printing plates that were then sealed vapor-tight and additionally foamed. The same again, because unfortunately our electrician forgot to tell us: put a KG pipe from the technical room to the utility room for the thick power cables; under the bathroom they are not allowed otherwise. (Of course, as clients, the coordination was our own responsibility, but it would have been nice if he had informed us in time.) So around outside, building boxes again, etc. So much for that topic...
Everything about your foils sounds good and nice, but I read nowhere that they are suitable and approved for application on the finished exterior plaster. That is exactly the "crucial point": How is a smooth adhesive tape supposed to seal waterproofly on the “crumbly texture” of the exterior plaster? Exactly, not at all. This only works in combination with, for example, the cartridge sealant I mentioned (which is also used for vapor barriers) plus the foil. Whether the whole thing will then please the builder as a complete construction is another matter entirely. Will the warranty be void because of this (I currently assume so), and if you then have moisture or heat damage at that spot – well, good luck.