ᐅ Waterproofing slurry or water repellent treatment

Hello everyone,

We have a damp base and efflorescence on the exterior render of the basement.

Structure:
Concrete basement – bitumen – 8cm (3 inches) perimeter insulation – mineral-based render – paint

I plan to remove the bricks in spring, install a cavity membrane, and in the process reduce the efflorescence.

Can anyone advise how to manage this with minimal effort? Some suggest using damp-proof sponges, others say that the render might no longer be able to breathe.

This is purely an aesthetic issue that I want to minimize. The basement is dry.

Thanks to all