Damp basement wall - How does the water penetrate?

Sealing from the inside is nonsense. Then you still get the water in but possibly not back out. A seal at the bottom only makes sense if it fully functions as a shell. Better to leave it as is and, during heavy rainfall events, give the ground the chance to release the moisture again.

Had a project like that a while ago and wasn’t sure how to deal with it... didn’t have to make a decision then anymore

What are you doing? It’s not your house? Seal it generally from the outside!

A sealing at the bottom only makes sense if it functions fully as an envelope. Better to leave it as is and give the ground the chance to get rid of the moisture again during heavy rain events.

Well, I want a dry basement, not one that soaks through from below the things I store there. The floor slab doesn't necessarily mind being damp.

Seal from the outside in general!

That’s difficult with a floor slab or the foundations. Hence the question of whether to additionally break the capillaries.

Well, I want a dry basement and not one that soaks the things I store there from below. The floor slab doesn't necessarily mind being damp.

Well, I'm not sure if that's something you'd want. I don't want anything in the house that I can only assume is still okay -- hidden behind bitumen. First of all, I wouldn't expect a 40-year-old floor slab to just shrug that off. Even small cracks + moisture are enough for the steel reinforcement to slowly but surely corrode away from under your butt stored goods. Secondly: Where does the moisture go then? Exactly, into the sides. Horizontal barriers and injections don't help there either.

We also have a very old house. At first, it annoyed me that we kept having damp corners from time to time. I decided to come to terms with it and to adjust storage in the basement accordingly. It's not optimal, of course. But a retroactive and reasonably economical sealing from below is virtually impossible. Under no circumstances would I now take measures based on the "what you don't see doesn't exist" principle.

As said, I wasn’t sure how to handle it, but to me it also somehow made sense that you could seal off the inside. The floor slab is moist anyway, with the dehumidification inside (that was intentional, since paper was stored there, we don’t need to discuss the purpose of that :rolleyes it just drew in even more moisture). In my case, the floor slab was also unreinforced (rammed) concrete, from around 1910.

What you don’t see isn’t there, doesn’t really draw in moisture either, because the reinforcement would rot away in that case too (there is always so much/little moisture when the floor slab lies directly in the earth without a separating layer), only that in that case you can watch it happen.

So do you have your floor slab lying there completely bare now?

Do you now have your base slab lying completely naked?

Bricks, which of course is a somewhat different starting point. The moisture passes through the joints almost as quickly as it comes. The cellar has been doing this for over 100 years now. I couldn’t gather anything from the existing plans, but it’s quite certain that it simply rests on the ground. It’s not constantly damp, but during heavy rain the groundwater or moisture presses in, especially at the wall/floor transition.