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    How can I add a backbox and a blanking plate onto expanding foam?



    Keeping it short here, I had a bottomless hole which I filled in with expanding foam with no issues. However, under that foam is some wires I wish to add a backbox and cover that with a blanking plate (So, it will act as a wire junction box) but how can I insert a backbox into foam?

    I have had two ideas 1, cut a hole and glue the backbox into it or 2, remove the foam and start again but this time was holding the backbox in place as I foam around it.


    Asked by Dave on 28th May 2019
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    Best Answer

    C Williams Electrical & Renovation Services

    "If you try and redo using foam to install the box it will push the box off the wall for the next few hours whilst it is still expanding.
    It will be easier to cut the shape of the box into the foam and use a grip fill type adhesive to fix the box and perhaps put in a few screws for a leveling point of view, not strength."

    Answered on 30th May 2019 - Member since Oct 2018 - report
    MAG Electrical Services Ltd

    "Start again and fit the backbox in place. Then foam the hole again."

    Answered on 21st May 2020 - Member since Apr 2020 - report
    Dino Electrical


    Better remove the foam, install a back box and make sure the wires are not completely surrounded in foam as will degrade the current capacity for the cable and it could be a risk of fire."

    Answered on 18th Jul 2019 - Member since Jul 2019 - report

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