New sockets, how deep?

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.
TIA
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Light switch back boxes can often be mounted directly, whilst a socket back box needs some block chopped out. It depends on the plasterer.
Christian.
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Trouble with plaster depth switch boxes is they restrict the choice of switch or dimmer. If you're doing a re-wire it makes sense to fit deep ones.
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*Also too, never, ever use repetitive redundancies *

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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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
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Chris French, Leeds

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They
accomodate
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.
Adam
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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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Chris French, Leeds

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They
Many thanks all. Best get the SDS out then :-).
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John Woodhall wrote:

Blimey, for breeze block?
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If you've got it , flaunt it...:-)
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Chris French, Leeds

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Perhaps your right. Dont want to demolish it do I.
But then again, gotta get your moneys worth. ;-)
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