Backbox Question

[Iggifer]

Looks like it could be thermalite behind 15mm of plaster if you look at the left of the box hole. Seems to finish suddenly though.

 

[conoral11]

Here are a few more shots, after vacuuming. I hope they help.

 

[conoral11]

 

[conoral11]

 

[stillp]

Never seen anything like that on an external wall.

 

[conoral11]

Never seen anything like that on an external wall.

Neither have I.

Should I cement the void up? Or is there a better alternative?

 

[stillp]

Are there any other sockets or switches on that wall? If so, are they the same?

 

[conoral11]

This room has a total of two single sockets. This one, on the exterior wall, and the other on an internal drywall

 

[sparkwright]

Bit odd.

Could it be a hollow building block that has got broken when the box was installed, and cavity wall insulation has found it's way in there?

 

[conoral11]

Bit odd.

Could it be a hollow building block that has got broken when the box was installed, and cavity wall insulation has found it's way in there?

Could be, the house apparently has had cavity wall insulation added a few years ago.

 

[sparkwright]

Did you notice any foam/polystyrene inside the old back box?

 

[conoral11]

Not inside of it. Just lots of sandy rubble around the box itself. Looked almost like someone had pushed the chunks back in...

 

[sparkwright]

I'm wondering if someone damaged the blockwork deep enough into the cavity when chasing the box in, then cemented the box in place.

When cavity wall insulation is installed, it certainly forms a quite dense wall of foam.

 

[Echo the husky]

They are likely insulated blocks, hollow and filled with insulation, if that makes sense. You used to be able to get them years ago, terrible design. We did a rewire in a bungalow with them a few years ago, they were a nightmare. OK for 25mm boxes chased in to the minimum depth, or if you chased in between 2 blocks, which is difficult to identify when covered with plaster! On the few deeper boxes, or where chasing went a little deep, 2 lengths of conduit was used as spacers to support the box, fixed with long screws. This meant the box was secure without damaging the insulation too much, then the boxes were plastered in in the normal way.

 

[conoral11]

Just to clarify this in my own mind, did your 2 lengths of conduit run horizontally, one above the other? And were they attached through the insulation material with the two screws?