I intend to wire in some new sockets for a friend in his conservatory. They
are going onto some breeze block which will then be plastered. How thick
will the plaster be. Do I need to cut out some of the block to accomodate
the thickness of the back box and the wires or will the plaster be at a
sufficient depth to hide the lot.
I usually work on a plaster depth of about 15 mm max. (which just about
fits a light switch box - 16 mm I think) others therefor need to be
sunk a bit. It's better to have then too deep rather than to shallow
Maybe the plasterer is using dot and dab. In which case a 25mm back box need
only be sunk by about 5mm and even then you will probably need extended
screws to fit the faceplate. The screws supplied for the cover are never
deeper than the back box they are expected to fit, but as been said you can
buy longer ones.
Whatever method, if you can follow the plasterer and use a knife/blade (but
not on your cables) to clear the plaster out of the back boxes leaving a
nice squared off finish before the plaster is dry then the faceplates will
sit very nicely on the plaster. It is a nightmare trying to clear out the
dried plaster from back boxes.
Not sayting you should leave it to dry if you can avoid it, but I've not
found it a great problem.
I use an old screwdriver (with a hammer if necessary) to knock it out.
It doesn't stick hard to the metal and comes off easy enough.
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