i have a plasterer doing work in my house at the momment.i want to have an arch in my doorway is it the plasters job to attach the mesh arch to the door frame or have i got too employ a builder to set it out as he keeps telling me i do.i thought he also should be using the metal angle beads around windows and external corners,he insists that this is not required is this correct.your help is very much appreciated.thank you.trish.