This video shows how to cut an internal mitre (for a corner that goes into a wall), without a Mitre Box:

  • Make sure you have the cornice the correct way up
  • Position the ceiling edge so that it is closest to you
  • Position the wall edge furthest away from you
  • Square up a line on the cornice
  • From the top edge of the line, take away the projection of the plaster coving and make another mark
  • You'll need assistance from another person to cut the actual mitre
  • Your assistant will need lift the back of the coving up while holding it at the correct depth
  • Use a saw to cut from the bottom edge of the coving to the top edge, taking away to create the internal mitre
  • Repeat the steps for the opposite end of the coving