On 20/02/2018 09:19, John Rumm wrote:

screws. If there is too much "irregularity", then mix up so (preferably
old) bonding plaster, slap it in the back of the hole, and bed the box
into it.

A trick I learnt some time back. Old plaster is no good for plastering
but it goes off in minutes so if you mix it quickly in an recycled
yogurt pot apply it to the back of the hole and then bed in the back-box
it will remain firmly in place within 5 minutes.

However it's not worth keeping your left over half sack of plaster just
in case it comes useful in the year to come.

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