Exterior wall damp, mold, joints sandy

Maybe you should first explain the framework conditions here. Presumably, the house is now your property? Inherited or purchased under what conditions. What do you plan to do with the property? Live in it yourself, renovate & sell, or something else...

Soft-fired bricks are normal for that period. They definitely require protection on the outside in the form of plaster or something similar. I have such an old exterior wall made of various soft-fired bricks (about 100m²) equipped with a curtain facade made of larch wood including 10cm stone wool insulation. Insulation on the inside is generally rubbish (but unfortunately also often present in my house, just construction mistakes of the past). A specialist is, as already mentioned, an advantage. Moisture must be kept outside as much as possible, but you must not make such a house too airtight (e.g., ventilation of supporting beams).

For my house, it has already been repeatedly recommended as a "renovation measure": "drive through it with the excavator" :)

A proper renovation costs a lot of money, that must be clear, a half-hearted one costs even more money, just over a longer period.

But old properties also have their charm... (for me, however, the old house mainly just gets on my nerves since I’m building new :rolleyes:)

I have already heard something about sakret; once in the workshop, an leveling compound from the manufacturer was processed. So we want to live in the house ourselves. I have bought it. In fact, this is the only wall that is only plastered from the outside so that you can still see the outlines of the stones, so relatively thin. The other walls are clad with plastic panels. Since in the roof area the wall or the mortar between the stones was much drier/firm, I assume the moisture is coming from below. Or from outside. From outside, plaster has partially peeled off so that the stones are already visible, so the wall from which the pictures were taken, I estimate this wall to be the worst. As far as I have informed myself, the insulation panels I had were made of tar/cork; when I removed them, the real mold smell only then came up. It should be added that the house was almost heated for a year. I am not completely without help; my uncle is an architect and would also give me tips. What options do I have now? Re-mortaring the joints, I have understood. Interior insulation definitely not. Initially, I would have sealed the wall from the outside and carried out a horizontal barrier using drilled holes and injection method. Does the insulation have to follow immediately from the outside, or can I take some time if it is at least sealed from the outside at first? I have seen systems where panels are glued from the outside and plastered; is that recommended? Can you also build a second wall from the inside or outside? What other systems are there?

Sorry for the amount of text and my ignorance, I am determined to see this through, working 18 hours every day: work+house+master school. Every morning when I get up, I can hardly wait to get started. Thanks for the answers and information.

Then the wall is almost completely exposed and who knows for how long already, and moisture will also come from below. No wonder the joints became so porous due to the moisture and there was mold. If the rest of the house is insulated, I would personally also insulate and plaster this wall in the same way (have it done....this is not for DIY). The injection method only prevents moisture from below, not from outside. You absolutely have to educate yourself about building physics, please do not just start insulating blindly. What kind of panels are those on the outside?

This is really a construction project that you can't just plan and execute quickly. First, slow down and think and plan properly. It will save time and money in the end! Houses from that year of construction usually have good substance and can become real treasures. But if you do something wrong there, in the end you will just have a moldy dump again after a few years.

Here you can see the spot where the plaster is flaking off. And the panels

And here again the same wall, only in the attic. The joints are not so easy to scrape out here. Still, it is not such a mortar as I know it, like stone hard. Maybe more sand was simply used in the past?

The house probably needs everything done anyway. Again: This can only be done with a professional! No one here in the forum can take that off your hands. These are not just detailed questions; you need to plan a full renovation as it seems. Talk to the architect and find some good craftsmen and do yourself what you can do well on your own. Demolition, floors, ceilings, walls, drywall, maybe also windows, interior doors and such things. But facade, moisture in the masonry, tiles, electrical work... and also statics, roof. You simply need professionals for that.