Fix Up for radiator hanging

[Pbuc]

First time post as we renovate our Victorian property :)

We are looking to hang a radiator on this wall but have been told by the plumber to strengthen for fixings. Any ideas or suggestions on filling the brickwork and getting back to a skim state?

Thanks in advance 

[Gone West]

@Pbuc Fill the gaps in the brickwork by packing in mortar, then a coat of bonding plaster out to 3mm below existing plaster and skim to finish with jointing tape around the edges.