I think its plasterboard, its quite thin (about 1/2 inch and then a gap into thin air, before outer wall.
It doesn't matter if I use a plug, that still spins around too because its so thin.
The screw is attached to the holdback so I can't use a different screw.
I can only think to put a thin plate on the wall with screws in that and hope it will add more bite or loads of filler ( it would probably drop down the gap )
New hold backs , looks like that’s intended for window frame fixing .Or drill wall and hammer in a wood dowel of about 10mm, though still a weak fixing .
Zero strength in foam and cement will crumble , main problem is tie backs are wrong style to use on the wall you have , you need with wall plate that accepts screw mounting .
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