I'm re-wiring a 1930's bungalow which must have been rewired in the 1960/70's(?). I've come across a old double socket backbox, which is 60mm deep and was mortared in - took the best part of a morning to get out!!I now have a deep hole (75 x100 x 150mm) in a single brick wall. How do I fill this so that I can get a modern backbox to fit?

You are lucky to have any brick left at the back. Is it *really* a single brick? What's behind it: cavity, another room, the outside air, something else?Probably best not to try to use screws and plugs into the back, but you should be able to "glue" it in place with all sorts of things. Mortar, plaster, car body filler? Probably not expanding foam, but you could glue it to the back with a dab of that, then run the wires, then fill the gaps with plaster or other filler to add some strength. Remember that ordinary plaster shrinks a lot, so if there is much thickness, do it in thinner layers letting each dry in between. Try to keep expanding foam or car body filler away from electrical insulation.

On 21 Aug 2021 at 16:25:33 BST, "John Rumm" wrote:Might expanding foam also work?

Vintage electrical backbox - how to replace?

Aug 21, 2021 Last reply: 4 years ago 21 Replies

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RJH 4 years ago

Might expanding foam also work?

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John Rumm 4 years ago

It could work, but has the disadvantage of "moving" while it sets, so you would need some mechanical restraint to keep the backbox in place for the duration.

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