"Bert Coules" wrote
| That makes sense, thanks; though I do recall on some past attempts
| that the brickwork had crumbled so much that drilling a hole before
| putting in the mortar was simply impossible. Probably I've just
| been unlucky with my walls. I take the point that it can be
| damaging to try to remove the box once the plaster's in and set,
| though.

If you have a bank of sockets etc to mount, join the back boxes together
rigidly with conduit couplers and bushes etc into a single rigid assembly.
(Check distance between boxes to allow room for faceplate overlap). Work
against a raised lip on a workbench and you will have the top of the boxes
in a straight line as well as the backs on a plane surface. Then cement the
whole lot into the all in one go.

If you mount your sockets a multiple-of-tile-size apart and know where your
tile joints will be on the finished wall you can get a nice regular tiling
pattern with no socket edge sitting close-but-not-quite on a grout line.

Owain