Joining plasterboard to sand/cement/plastered block wall

[andreas]

Excuse the drawing, no architect here ha.

Blue lines are block walls of room that are sand/cement/plaster finish. At some point someone made a boxed in area (red colour) for services. The covering of the box is a bit crap, out of alignment with the block wall and damaged. I am going to strip off and put new plasterboard covering on then skim all the walls where the pink lines are.

What is the best way to join the plasterboard to the existing sand/cement/plaster finish, where the green arrow points? The existing plaster  on the block wall is damaged on that join but the sand/cement underneath is fine. I was thinking chip off a couple of inches of plaster, SBR the sand/cement mix, apply mesh tape over plasterboard edge / sand cement then skim whole wall?

 

[JohnMo]

I would do a timber structure attached to wall and then skin with plasterboard 

[Nickfromwales]

1 hour ago, andreas said:

Excuse the drawing, no architect here ha.

Blue lines are block walls of room that are sand/cement/plaster finish. At some point someone made a boxed in area (red colour) for services. The covering of the box is a bit crap, out of alignment with the block wall and damaged. I am going to strip off and put new plasterboard covering on then skim all the walls where the pink lines are.

What is the best way to join the plasterboard to the existing sand/cement/plaster finish, where the green arrow points? The existing plaster  on the block wall is damaged on that join but the sand/cement underneath is fine. I was thinking chip off a couple of inches of plaster, SBR the sand/cement mix, apply mesh tape over plasterboard edge / sand cement then skim whole wall?

 

Do exactly as you say, but instead of sand and cement I use dry lining (dot & dab) adhesive which is far more robust and doesn't fray like S&C does.

 

Use a load of plasterers scrim tape to bridge between masonry and new works, and wherever fixings timber back to masonry, use plenty of solvent free gripfill behind the timbers when fixing them back to the wall, which will go off rock solid.