Repair and plaster wall

[Klonkkalle]

Hello! I'm about to repair my wall and then plaster it. Some of the stones have started to fall apart, so I need to fix them first. But I'm wondering how to go about it. I have absolutely no idea what's best to use for any of the steps I need to perform.

For the plaster, I've been told to use a or b plaster mix, and then someone else says I should use c. So I would like some explanation on what would be preferable in my case. Thanks in advance!

(I don't know if I started the thread in the right category, so I apologize if it's in the wrong place)

 

[Stefan N]

Had gone with A or possibly B, C won't last long there. But you need to stop the water that's running down into it in any case.

 

[Klonkkalle]

Would have gone with A or possibly B, C won't last long there. But you do need to stop the water running down into it in any case.

Okok thanks! Do you have any tips on mortar to repair the stones with?