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

 

[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.

 

[swaRRR]

Plasterboard adhesive - doesn't shrink when it dries so it's perfect for this application. Whack it in there, sink your metal box into it so it's flush and let it dry. Make sure to grommet your entry hole before putting the box in or make sure the entry hole is completely free of adhesive before you walk away from it.

 

[Mike Johnson]

This stuff would be far better and will not allow the box to pull out with the plug: Rawlplug R-KEM II Styrene-Free Polyester Resin 300ml - https://www.screwfix.com/p/rawlplug-r-kem-ii-styrene-free-polyester-resin-300ml/32863?

 

[Welchyboy1]

Just done a Rewire exactly like this, literally finished it yesterday

knock the horizontal lips off the adjoining blocks flat to the back then
just cut 2x 4 inch piece of 1x1 wood batten(stuff that’s used in packaging for integrated ovens is best) and liberally no nails them to the flat back of the blocks(one above and below the horizontal lip of the block is best but it’s gonna depend on whereabouts you chase in) don’t try to glue them to the rough lip only the smooth flat bit!!)

leave it until the next morning then just fix your metal standard back boxes with 1in x8 screws

sorted and solid as a rock, if you use 35mm boxes it should work out near as damn it to flush of the wall

when I bond the chases afterwards I always make sure I squeeze loads in around the socket boxes to give it that bit of extra support but it’s fine honest!!

if you think your gonna cut a plasterboard box Into it your dreaming

 

[Mike Johnson]

Strange been doing it for the past eleven years without dreaming.

 

[Welchyboy1]

Strange been doing it for the past eleven years without dreaming.

Out of interest what multi tool blade would you use to cut through brick?

 

[Mike Johnson]

We are talking about terracotta hollow block not brick, but for the hollow block I use a Carbide tipped hole saw to start and then these to trim the hole : Carbide Coated Blades for Fein, Bosch, Makita Multitools | Saxton Blades -

 

[telectrix]

We are talking about terracotta hollow block not brick, but for the hollow block I use a Carbide tipped hole saw to start and then these to trim the hole : Carbide Coated Blades for Fein, Bosch, Makita Multitools | Saxton Blades -

you lost your hammer then?

 

[littlespark]

Out of interest what multi tool blade would you use to cut through brick?

Someone else’s.

 

[Mike Johnson]

you lost your hammer then?

Its all I can do to hold my own, let alone a hammer these days.

 

[mainline]

Strange been doing it for the past eleven years without dreaming.

Just wondering if you have finished it yet ?