plastering new stud wall to existing

[cully]

I am reducing the ceiling height of a shower enclosure from 2700 (existing) to 2200mm which means I will have the "upper part" of a stud wall 1400mm width X 500mm depth between two plastered block walls.
My concern is when this stud is plastered how do I address the issue of cracking between new plaster (stud) to old (existing)??
Thanks

 

[dontbelieveawordofit]

scrim tape all the joints.
scrape off anything loose or weak and blue grit or gyprime the existing block before skimming.

 

[cully]

Thanks Benny
The "old" plasterwork isn't that old and is secure to the wall but I realise that it becomes a weak point for cracking.
It's a pity I can't overlay the 1400 X 500mm stud with something other than plasterboard that wouldn't move that I could paint.