House from the 70s - Assessment of mold inside!?

In my opinion, this is not mold. The wall is dry and looks healthy. Obviously, you haven't seen mold yet. Any possible mold exposure can be measured. The gray-black substance under the wallpaper is usually wallpaper glue. It just ages like that over the years. And regarding thermal insulation, the 3 cm of polystyrene under the drywall don't really make much of a difference.

I don't know if it helps, but my experience report regarding internal insulation: We also had such Styrofoam insulation and in one room, in the baseboard area, there was mold under the wallpaper. Since the seller of our house messed up most of what he touched, we tore everything out on the ground floor. There actually appeared no or surprisingly little mold. So maybe it could have been left alone? Maybe we would have only had problems in 5, 10, 15 years (the internal insulation was only installed in 2016)? On the 1st floor, we have the same wall structure and are actually considering not tackling this construction site immediately after finishing the ground floor (we live on the 1st floor and are renovating the ground floor, so it is not possible at the same time...), but rather first enjoying a house with little construction dust. However, I am absolutely not in favor of the Styrofoam with drywall solution, especially since, as in our case, it is not even glued over the entire surface, but only in wart-like spots... On the ground floor, we have started to install pure lime plaster (used as insulation plaster with expanded glass on the exterior walls). I'm curious if we will notice a difference in indoor climate/well-being when we compare upstairs and downstairs. This may then also influence the decision for or against a timely second construction site upstairs. But it's clear that it will be done eventually. The stones in your photos really look good, so I wouldn't be immediately deterred. What kind of heating do you have planned? If the screed is already out, possibly underfloor heating? Then it would of course be good if the house is well insulated... Just discovered the neighboring thread, have you already?

Thank you for your crystal ball assessment. What would be, for example, proper measures? What kind could these be? Repainting? Mold remover? Or what is usually done/meant here? ..I just want to prevent an elaborate interior demolition and then finding out afterward that it is mold which is harmful to health. I do not want to fully insulate the exterior facade due to the genuine visible clinker bricks. That would also require replacing the windows, which would then exceed the budget. Regards & thanks in advance

I don’t see any critical mold there, it looks different. With 3 cm of styrofoam interior insulation and drywall panels and textured wallpaper ... I would throw it all out and rebuild properly if you are planning to renovate the interior anyway (water, electricity?) Your wall construction, from the 70s (if before 1978), is probably 11.5 or 17.5 cm calcium silicate bricks (visible in the photos), cement mortar in a strong mix (approx. 1 cm), clinker as facing. This was the usual cheap construction method at the time. Maybe the 3 cm styrofoam was already installed during construction or possibly later, but it looks like it was installed at the time of erection. I would also not recommend exterior insulation on clinker facades. The 3 cm interior insulation beneath drywall is unfortunately the cheapest and most botched construction there is. Little effect with only 3 cm, probably a building physics mess since there is no vapor barrier and many penetrations (sockets, switches, etc.) and it is unfavorable for indoor climate because the mass of the walls is no longer available as heat storage. I would recommend removing everything except the calcium silicate bricks and then rebuilding. You can then use capillary-active, diffusion-open insulating materials and apply them to the wall in panels. Wood fiber insulation boards or hemp boards are suitable here. You can then reroute water, heating and electrical installations beforehand and, for example, simply mount sockets directly on the calcium silicate bricks and then cover them with the wood fiber (at 60 mm thickness). With thicker insulation just lay the cables and then use suitable wood fiber sockets. Be sure to close radiator niches flush. No mold, warm house, ecologically harmless, and better room climate due to the high specific heat capacity of wood fiber. For plaster and paint then also be sure to use diffusion-open materials like lime or clay plaster and lime, clay, or silicate paint. For the insulation thickness, the Building Energy Act does not specify a minimum thickness unlike for all other insulations. 6-8 cm already lead to a U-value below 0.5 and at 10 cm you reach 0.3. Anything beyond that strongly reduces the living space. The only thing that should be checked are the joints on the weather side of the exterior wall. They should be in good condition and renewed if necessary. Because of the cold exterior walls, moisture cannot dry out as well there and the penetration of driving rain should be avoided.