When gluing broken plastics together its best to lay the broken parts on a
flat surface so the two pieces bond together flat. The problem is that the
glue will adhere to the flat surface and the plastic will be bonded to the
surface. To stop this, put a piece of wax paper between the surface and the
plastic. The wax paper will pull off easily when dry and any wax left on
the plastic won't matter because it's transparent.