Hi team 🙂
I've just had an electrician round who's installed several powerpoints in different rooms.Â
For the new powerpoints installed on internal walls, he chased along the concrete walls (see photos #1 and #2). 


However, for the powerpoints installed on walls that are also external, he holed into the wall and threaded the electrical through the cavity between the internal wall and external wall. See photos #3 and #4. The holes that are now left in the wall is about 12cm wide x 14 high and 12cm deep.



How do I fill in these large holes without also filling in the cavity between the internal/external walls?
What products should I use?
Thanks in advance!