A large portion of the underside of the upper chamber ceiling blocks seems to be coated in plaster varying from large gobs applied into and around the block joints down to a few mm to zero on the block surfaces. It looks like the rafter blocks were placed unevenly and then rendered to provide a smooth and even interior surface.
The render could not have been applied to the blocks prior to their installation.
The cartouche is on top of the render, indicating that it was applied in situ.
It's good that Colette confirms this.
Edited 1 time(s). Last edit at 05-Oct-16 13:27 by Jon Ellison.