How to make surfaces?

[Trojadam]

Hello kind building friends! The pictures are from a storage space in the main building where I plan to fix the surface. It's a split-level house, so this is the wall facing the ground. The house was built in the 60s, and the plaster is peeling in places where I have removed the woven wallpaper. I'm not very experienced with masonry and material choices, but what do you think is the best strategy to achieve the final result? It doesn't have to be perfect! Some type of mortar? Coarse filler from Biltema?

Grateful for advice!

Best regards,
Adam

 

[fribygg]

Knock away all loose material and re-plaster.

 

[Trojadam]

Knock away everything loose and re-plaster.

Is it difficult for beginners, do you have advice regarding product selection?

 

[fredand44]

Maybe this instruction can be helpful.
https://www.byggmax.se/putsa-på-murblock
I believe, with emphasis on believe, that it works with putsbruk C (or if it's called murbruk C).
Best regards, Fredrik

 

[Trojadam]

Thank you very much, sounds like a perfect instruction!