Electrician's shafts - how to fill them?

Hello everyone,

we are building a KFW 55 house. Now a question has come up for us: Should the shafts that the electrician has installed for the cables be filled with a special mortar (insulating or similar), or is it sufficient if it is just "normal" mortar?

Best regards,
Ramona

Are they unused?

Sorry, no, there are cables inside. However, something would have to be filled in before the interior plaster.

Do you mean special shafts now, or the normal slots in the walls?

I mean the normal slots.

Under no circumstances use mortar... it will just deform everything later... just use bonding plaster, e.g. Rotband