ᐅ Waterproofing the Basement of an Older Building from the Inside?

In our older building (constructed around 1920, with brick walls, clay, and other materials), the exterior along the street side was excavated about 10 years ago and treated with appropriate plaster, bitumen coating, dimpled membrane, and similar measures for renovation—or at least an attempt at renovation. However, it seems it wasn’t done completely or thoroughly enough. (The contractor responsible for the groundwork is no longer reachable.)

Anyway, there was again rainwater in a basement room after an intense downpour, which seems to have penetrated through the wall or under the basement floor from outside.

I’m reluctant to excavate from the outside again, so my question is: what is the opinion on interior waterproofing systems offered by various renovation companies? Usually, these are franchise businesses—is this a viable alternative? If so, only one wall in a basement room facing the street is affected.

Since the house will most likely be sold within the next 10 to 15 years, I’d prefer to have documentation from a professional company to prove the work was done, rather than having to say I fixed it myself.

I recommend this thread on a similar topic – you’ll need to draw your own conclusions from it. (Spoiler: It’s best to get used to the idea that your options are limited). https://www.hausbau-forum.de/threads/massnahmen-wg-feuchtem-keller-unterschiedliche-expertenmeinungen.39170/