Hi people,I've just took a lot of tiles off in my daughters bathroom...most of it will be plasterboarded but some of the walls are to be just painted...I am getting them ready...but in places the plaster skim (I think it's called that) has broken...I have removed all the broken bits but some of it is really stuck fast and will not come off unless I chisel it off (see pics) it really is on there very firm...question is do I need to remove it also for it to be replastered ?