Filling chases and blown plaster

[MrPie]

Hi guys, got a little project going on to mount a TV above a fireplace iwth a mantel. Decided to get power hooked up as well as a conduit for wiring. The areas marked red are loose/blown plaster. What would be the best way going about this? i've done patch work with plastering. Will be ripping the loose plaster off and then using diluted PVA. Couple of questions though,

How long should i wait before plastering after PVA'ing?

Should i Just use bonding plaster and level it out with the existing plaster in one go or bond it leaving a 2-3mm depth gap, scratch, and then do another coat on top?

Will be wallpapered over

Thanks!

 

[MrPie]

So looks like a lot more came away with little effort in big chunks. Its not all plaster. Does anyone know what the slab in the second picture is made from? Will be removing dust and PVAing today

 

[Lee dorey]

Your best option as need mesh joins is run straight edges and cut slowly in layers with sharp blade then carefully remove old skim then pva the lot and skim but on the brown patches let pva set then skim or skim tacky

 

[Lee dorey]

Hardwall or bond deep areas obvs and pva depending on what suction type plaster is used

 

[Wayners]

Is that an older property with lime plaster and the it's been renovated (skimmed) and the gypsum has not taken to it then blown off?