Best way to fill crack

[Burgo99]

OK,have started to remove wallpaper and radiators ready for redecorating.
Once removed I found this behind the rad. I have removed all loose material but as it is where the radiator bracket was and probably going to be again, i am wondering best solution for strength. Deepest gap is 45mm,but think this is where an old bracket fitting was. Generally its no more than 15mm deep.
Thank you.

 

[blup]

I have found this effective in filling deeper holes, ideally you need to build it up because there is some slump

Blup

 

[Burgo99]

Will it be strong enough to take radiator brackets sgain ?

 

[John D v2.0]

Will it be strong enough to take radiator brackets sgain ?

No, that's decorative , for fixings for something heavy you would really need to fix into sound masonry. Just get longer fixings, move the rad slightly or bracket, or fix a plate th the wall and fix the bracket to that.

 

[blup]

Treat it like plaster i.e make sure the fixing used is deep enough to pass through into the brick or block below. It's harder than plaster though.

Blup