What should I use to repair the sides of a concrete staircase?

[JeLö]

Hello,

I'm going to try to repair the entrance stairs. I've never worked with concrete/plaster/cement before, so I have no idea what to use or how to proceed.

What needs repair seems to be an old patch that has come loose and appears to be some porous plaster. Gypsum plaster? A similar patch on the other side is holding but sounds hollow when tapped.

I understand that all loose material needs to be knocked away, but what is the next step? And which product(s) should be used to fill the cracks?

 

[Drburr]

Knock off all old repairs, if any reinforcement sticks out, brush it off with a wire brush. Rust protection paint.

Then adhesive type
https://www.k-rauta.se/byggvaruhus/vidhäftare-weber-saint-gobain-1l

Afterwards, apply ardex A46, and float it over. This is a cement-based fast filler with an emphasis on fast. The open time of the compound is around 10 minutes, so mix a little at a time.