According to Calvin Henry-Cotnam :
Chris Lewis ) said...

According to GoHabsGo :
"Rick" wrote in news:9DGlf.822$Dd2.412

There are also adjustable boxes available so you can set them flush
after finishing the tile....

If it's an existing box, and you're simply tiling around it, you'll
find a box extender by far the easiest and cheapest solution.

Typical wall tile only adds 1/4" to 3/8" thickness, which is quite a bit
less than typical box extenders.

If that is the case, just tile around the opening (with the outlets either
removed or hanging -- power off!), using a tile nipper to create the little
half-circles to accomodate where the outlet screws are located at the top
and bottom of the box opening.

Heh. In this particular case, it's more a matter of taste ;-)

Canadian electrical code sez you cannot have flammable materials exposed
to the inside of the box. Which means, for example, if this is in wood
panelling[+], you must use a box extender, you cannot expose the edge of
the panelling to the interior of the box.

Ceramic tile, of course, is non-flammable. So, provided that none of the
rest of the exposed edge is flammable, you don't need an extender.

But I don't like it ;-) Potentially sharp edges, more finicky cutting,
higher dust incursion etc.

A few days ago I installed beadboard strips in a bathroom. Real wood.
Box extender mandatory.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.