ᐅ Renovating a sandstone basement from both the outside and inside

Hello everyone,

As always, there are different opinions, and I would like to hear your advice or experience on this (read your input).
I have purchased an older house with a sandstone basement – one side is underground and therefore damp. Now I want to dig out the outside and protect the wall from moisture with a dimpled membrane.
Someone told me I should also apply a protective coating such as tar paint or a waterproof slurry to the sandstone wall before attaching the dimpled membrane. My question is: is this correct? I thought sandstone should not be sealed.

On the inside, I want to plaster the sandstone and was thinking of using clay plaster since it is breathable and can handle moisture well – what do you think about that?

I want to completely remove the old floor (various concrete slabs and natural soil) and re-pour it with concrete to get a clean basement. Since the floor is somewhat damp, I believe a layer of gravel or crushed stone under the concrete is necessary, and possibly also a membrane as a moisture barrier?

I would appreciate any suggestions.

Jürgen