Question about repairing blue concrete and concrete floors

[Noas]

Hello!

I am renovating my first apartment and have a few questions that I hope someone could help me with.

I have channeled blue concrete walls so that the electrician can pull wiring and wonder if I can fill them with gypsum mortar since the walls are going to be skim coated anyway, or should I use plaster since the rest of the wall is plastered? Do I need some kind of primer to make the gypsum mortar stick?

My next question concerns the floor, which I have also channeled. It consists of a concrete slab with sand underneath, some of which I accidentally vacuumed away. Is it enough to fill with new sand and pour again, or is there something else I need to do to patch up the floor after the electrician?

Thanks for the help!

 

[Stefan N]

Water first, then it's fine with plastering.
For the floor, you can use sand then self-leveling compound.

 

[Noas]

Water first then gypsum plaster works well.
For the floor, you can use sand and then self-leveling compound.

Sounds like a good alternative! Do you need to prime the sand/floor before using self-leveling compound?

 

[Noas]

Water first, then gypsum plaster works fine.
For the floor, you can use sand and then self-leveling compound.

What kind of sand should be used and should you water the sand or something to pack it?