ᐅ Concrete base of garden shed is crumbling – What can I do?

Good morning everyone,

We have a self-built, self-plastered garden/tool shed.
I think I made a waterproofing mistake... the plaster on the base is discoloring and peeling off.

Brief description:

- masonry wall
- base then coated with a waterproof slurry
- then covered with a lime-cement plaster
- then painted

Where the paving stones have now been laid right up to the wall (a drainage membrane is present), the plaster is absorbing moisture, discoloring, and already crumbling in some places. I assume I should have applied some kind of additional waterproofing where the paving meets the wall. It’s already done now.
I have partially removed the paving to allow it to dry and to prevent further damage.

What can I do now?
Is there a "simple" solution? And what would be the perfect solution?

For me, "simple" would mean treating the wall below the ground level/paving surface with something like waterproof slurry? Bitumen coating?
Then repairing and repainting the damaged plaster areas.

Or do I need to take the full approach, meaning removing the plaster above (up to the damaged areas), replastering, and then applying the appropriate treatment?

What do you think?

Thanks and have a nice Sunday

Hello!

Does anyone have any ideas or opinions on this topic?
Thanks!