Insulation: Water ingress from a small hole in sandstone basement wall

hello, I have a basement with sandstone walls. There is a small hole in one place through which water comes in from outside. After heavy rain, a 3-5 m² puddle forms, rarely more. The water comes from the hills; underground there are watercourses and one of them runs at this corner of my house. The basement floor is about 1.5 meters below the street surface. The watercourses have existed for about 10 years because the underground watercourses changed due to a large construction pit nearby.

now I want to fill the hole with cement and apply some cement to the wall about 40x40 cm and dry it with a heater. Is cement suitable for this? Sealing the entire wall apparently makes no sense, because the rest of the wall is dry, between somewhat more than iron dry. There is a slight moisture, but low. In addition, sandstone is supposed to absorb water.

Can someone tell me which material and tools might be suitable?

Pozzolanic or air lime mortar
Ordinary cement will not work
It becomes too hard

I pried out the old joints with a mini hammer. Behind that was often sand and soil which I scraped out and rinsed with water.
Afterwards, I packed pozzolanic mortar into the joints. Professionals throw the mortar – I can't do that.
I pressed the mortar in with the help of a spatula and a joint spatula. If you have wide and/or deep joints, you can set small sandstone pieces (broken) in between. That should provide stability. I filled the joints first, then pressed the stone in.

Pozzolanic lime mortar or air lime mortar
Regular cement doesn’t work
It becomes too hard

I chiseled out the old joints with a mini hammer. Behind them there was often sand and earth which I scraped out and rinsed with water.
Afterwards I packed the joints with pozzolanic mortar. Professionals throw the mortar – I can’t do that.
I pressed the mortar in with the help of a spatula and a joint spatula. If you have wide and/or deep joints you can place small sandstone pieces (fragments) in between. That is supposed to add stability. I filled the joints first, then pressed the stone in.

Thank you very much, what ratio should mortar and rubble stones have? 2/2 or something like that? Can you also apply it with a cartridge gun, like you do with silicone?

What do you mean by the ratio of rubble stones to mortar?

There are mortar pumps that cost. Then there are fixed nozzles, with which I would have gone crazy. I don't know how even the stones or the joints are in your case. Here I had actual holes that kept filling up more and more.

hello, which stones (small sandstone pieces (broken) exactly do I use for the mortar filler mixture and where can I get them?

Hm good question. I took the ones that were washed out of the joints and those that I have plenty of in the ground. Take the [Trassmörtel] without stones and done.