Dear Adam, Since you do not mention whether the coving is moulded or not. I'm hoping this advice helps. If you start on the level edges of the walls which are not on the bend of the corner; and work towards the middle of the bend from both sides using gradual cuts of the plaster instead of trying to cut the plaster to fit round the corner. (If you was trying to bend the plaster around a corner and it was not moulded, you could use two breeze blocks, to form the bend with plaster suspended on top. This would form natural arch overnight you would have to use 9mm plaster but only if plaster was not moulded) I personally would try and cut small sections to fit round the coner until you have nearly met each piece. Bear in mind where there are any gaps you could use fingers to form rest of coving mould ;or make your own coving design to suit. Take care not to snap plaster when trying this. Cut small pieces to fit round corner. Good luck
Anthony Tovey, September 2010