Made hole into cavity while hanging blinds

[Astronaut_elvis]

Installed some Venetian blinds in window recess and then discovered it was too close to the window and caught the handles. When I’ve moved the fixings forward I’ve gone through the plaster into a void which am assuming is the wall cavity. I guess I thought it would be blocked off with something solid, the other side was no problem.

Any ideas what I can fill this with so can then put fixings in? I thought perhaps gripfill as at least it would dry quickly but not sure if it’s solid enough to hold fixings.

 

[Wayners]

Toupret standard powdered filler.
Give it 24 hours to dry then drill but not on a hammer setting.
Push well in. Id have an extra thick mix as well