Back Box In Hollow Wall Installation

[mackatoon]

Hi Guys, I've completed rewires with hollow walls before and was able to use a dry line Box. No chance of being able to use them this time.

I've never seen walls like this though. Just wondering how people have installed back boxes in this circumstance? I've attached a pic

I'm assuming Fire resistant Expanding foam or Plaster? Prob need the version which dries the quickest as ill need to start runnung cables asap.

Your helps appreciated

Andy

 

[Mike Johnson]

Not only finished, but still using the same blade.