after checking a few tiles at the window area i had a few loose tiles which i took off to investigate. the window wall seems to have been made up of plasterboard and then a skim of brown plaster on top with a plastic wire mesh stuff inside it, downwards from window area, which is different from the side walls where this is made up of about an inch of white plaster, not sure if there is any mesh inside it but in comparison seems a lot thicker and better stability that the brown plaster on the window wall.
from where the tiles were loose there seems to be no mesh in this area towards the ceiling and side areas of window. when i pulled a few tiles off, the thin layer of brown plaster came away with the adhesive and was very weak however the rest of the wall seems intact and ok. im assuming that when this was done the need for this wire mesh was missed out left and right side of the window.
also, im not going to use the mapei super grip on last wall. so what stuff should i buy going forward from b&q or screwfix or anything else to help finish this job
thanks for your time guys