Back Box In Hollow Wall Installation

[littlespark]

I don’t know if anyones mentioned it…. But what about surface trunking and a pattress box?

It’s good enough for some council rewires…..

 

[telectrix]

but as electricians, we should be proud of our work. if it don't fit using normal methods, sort it properly. there are no problems, only solutions.

 

[Mike Johnson]

What is preventing you using a dry lining box?

 

[GBDamo]

What is preventing you using a dry lining box?

You'd have to diamond cut/grind each one precisely and hope you hit a void perfectly every time, nigh impossible.

As mentioned above, I'd cut them out as in the OP and then set the boxes in some bonding or drywall adhesive. If they're set well they shouldn't need any further fixings.

It's not going to be quick though, it's one of those jobs that if you try to rush it it'll take twice as long.

Needed to chase and set the backboxes then given them 24hr to go off before trying to pull cables through. I fear they'll just come lose otherwise and then you'll be spending twice as long trying to secure them.

Absolute nightmare stuff. We had one wall to deal with, tried batten and board but could get a fixing for the batten, ended up using drywall adhesive to gob the backboxes to the wall then dot and dab board up to the back boxes.

If there are more than a couple to deal with then I'd be revisiting the price with the customer.

 

[Mike Johnson]

Easy enough to cut and take out any obstructions with a Multi tool, it will only be a dividing flange, as long as the hole is accurate in width the sliding side fixings will fit and hold well, even used dry lining box's in a ceiling, yes terracotta hollow block ceilings, pull cord for the lights in the shower and the fan isolator switch.

Don't chase for the conduit/cable feed from above and below through the hollow block, just knock through each top and bottom with a long rod and yes I have done this as its common practice in countries that use the hollow block wall construction.

 

[OnlQQker]

Back box wedged in hole and expanding foam is the only way I'd play it, as mentioned above!

 

[Pretty Mouth]

Don't chase for the conduit/cable feed from above and below through the hollow block, just knock through each top and bottom with a long rod and yes I have done this as its common practice in countries that use the hollow block wall construction.

Can you describe this in more detail please Mike? I can't quite visualise how this works (the cells run horizontally), but it sounds like it would be usefull.

I come across this type of blockwork fairly regularly. It seems like it was a popular material round here sometime in the 60s, usually used for the inner leaf of cavity walls, but also internal walls too. It's a pain to work with, particularly when it has only a thin coat of plaster covering it and you have to chase it out.

The cells run horizontally, so

 

[OnlQQker]

Structural Terra Cotta

AKA structural tile, hollow tile block, hollow building tile, structural clay tile and structural clay load-bearing wall tile.

historicbldgs.com

 

[Other_Tucker]

All day everyday doing council kitchens, I use the double+single dual 35mm backboxes because their so wide you can get at least 2 screws into the protruding parts.

I have to fill all the holes and chases with bonding anyway, so the other option is run the cables, fill the cavity with bonding/hardwall and just push the BB in until it extrudes out like toothpaste.

If you're good you can drill vertically through all the voids and pop out the bottom, although watch out for it being one layer thick sometimes, the rear part being what's plastered for the room next-door. It's still preferable to solid red brick chasing

 

[Mike Johnson]

Can you describe this in more detail please Mike? I can't quite visualise how this works (the cells run horizontally), but it sounds like it would be usefull.

I come across this type of blockwork fairly regularly. It seems like it was a popular material round here sometime in the 60s, usually used for the inner leaf of cavity walls, but also internal walls too. It's a pain to work with, particularly when it has only a thin coat of plaster covering it and you have to chase it out.

The cells run horizontally, so

I thought that was enough detail, but I use a piece of reinforcing rod and a club hammer, according to how far up or down you need to go, it may be necessary to drill in an intermediate rodding point, you only have to go through the top and bottom of the block, bit of a pain to do, but not as much work afterwards to make good.