Chasing Electric Cables into Breeze-block Wall

[OneAvocado]

As part of smartening up a spare bedroom I'd like to recess an electrical socket and have the electrical cable chased into the wall.

I'd get somebody in to do this but I'd like to be clear about what is possible and how things should be done before I start asking for quotes.

My worry is that the wall seems to be a single breeze block construction (1950s flat) and as the room on the other side of this wall has been newly skimmed and finished I want to avoid anything going right through the wall and affecting it.

To be clear - the breeze block seems rather thin. When a socket in an adjoining room was being (amateurly) recessed it caused some damage to this wall (not an issue as the damaged wall will be skimmed).

There is also an electrical socket and cabling running along another external wall however this wall is much thicker and I don;t believe there should be any complications for this.

Any advice or thoughts to get this going would be very much appreciated!

Many Thanks!


Here's a pic of the wall in case it helps at all:

Untitled

• OneAvocado
• 17 May 2013
• 1

 

[sparkzzz]

Chopping in should be fine, as long as its breeze and normal thickness it shouldn't matter the box should fit flush with the wall finish. Boxes are only 25mm deep and if done carefully will not damage the other side of the wall.

 

[Iggifer]

if you're changing the carpet, run the cable under the floorboards as much as possible, much easier

 

[OneAvocado]

Thanks for the replies.

The floor is concrete so unfortunately that's not an option

 

[PrenticeBoyofDerry]

May I add to previous comments that have not covered the following?:
There are building regulations regarding depths of chases in solid walls and wiring requirements, regarding the permitted safe routes and protection of cables.

In brief:
*Horizontal chase depths, no greater than 1/6th of the thickness of wall (skin/leaf)
*Vertical chase depths, no greater than 1/3rd of the thickness of wall (skin/leaf)
*Permitted safe routes as links:
//www.diynot.com/wiki/electrics:installation_techniques:walls
//www.diynot.com/wiki/electrics:installation_techniques:route

As the cable is now being buried within wall, the requirement for 30mA RCD protection, may need to be added to the cable being buried. If the cable is buried less than 50mm within wall and without mechanical protection (this is achieved by use of metal conduit or integrated mechanically protected cable), then RCD will be required.
It maybe that this circuit is already covered by 30mA RCD protection at the consumer unit or via a RCD fused connection, this requires verification.
It is also now a requirement that any newly installed domestic socket outlet, is also protected by 30mA RCD, regardless of provisions made for protection of cable.

 

[pjcomp]

I recall in my early days chasing a socket into a single-skin breeze block wall. As I energetically pounded at it with the chisel the hole was getting deeper but I didn't seem to get much debris from it. Checking in the next room I found the breeze block sticking out of the wall ...

Go carefully

PJ

 

[mfarrow]

There were blocks out there with a lot less than the 100mm standard thickness at one point. Make sure the wall's thick enough. A test hole might be appropriate if you're unsure, you can use the drill bit as a thickness gauge if you've no doors/windows on the wall.

Otherwise if you're worried, stitch drill first before going at it with the chisel.

 

[davelx]

There were blocks out there with a lot less than the 100mm standard thickness at one point. Make sure the wall's thick enough. A test hole might be appropriate if you're unsure, you can use the drill bit as a thickness gauge if you've no doors/windows on the wall.

Otherwise if you're worried, stitch drill first before going at it with the chisel.

Indeed - in my house (1930 build) they are 75mm!

I was chasing out for a shaver socket in the bathroom and hit the chisel a little too hard at too steep an angle and it disappeared through a chisel sized hole and flew down the staircase the other side, together with a large lump of plaster and wallpaper!

 

[RF Lighting]

There are some ex-council houses near me with 50mm internal block walls. They take some very careful chopping into!

 

[phatboy]

I wouldn't recommend a 25mm backbox for a socket, especially if its got 2 cables in it..... very fiddly to get the faceplate on flush, without squashing anything. 35mm all the way, definitely if you want to use flat-plate sockets

 

[SimonH2]

The trick with thin walls is not to go at it like you're trying to bring down the Berlin wall.

Stitch drill round the box to the depth you need, and also randomly drill inside the rectangle to take some of the strength out. Then go slowly with a sharpish chisel - just slowly knowing small pieces off. The drilled holes will give you a depth gauge. A smaller chisel will give you a higher contact pressure for a given blow than a wide bolster.
If you start a run where there's a drilled hole, it helps you get started, get a bit of a recess, then carefully knock so that the chisel is breaking bits off the side of it into the hole you're expanding. Hard to describe, it's one of those things that with a bit of practice you "just do" without being able to say what you're doing.

Recently had to do that in my mates bungalow. The other side of the wall was his fully finished (skimmed, painted etc) living room - and I was sinking 47mm boxes to ensure plenty of wiring space.

 

[phatboy]

I wouldn't do it by hand, too slow and painful!

Grinder to get the box shape, and then divide in 4, then use an SDS chisel to dig out the box.

 

[SimonH2]

... then use an SDS chisel to dig out the box.

Followed by plasterer to repair the other side
While I'm sure it can be done with SDS chisel, it needs a level of self control and dexterity that (keeping things polite) I think most people lack.

 

[phatboy]

... then use an SDS chisel to dig out the box.

Followed by plasterer to repair the other side
While I'm sure it can be done with SDS chisel, it needs a level of self control and dexterity that (keeping things polite) I think most people lack.

I find it easier to be honest! Instead of thumping with a lump hammer and getting knackered, you angle the SDS chisel at about 45degrees, and push each direction with light - medium force. I can usually get the back on the hole pretty flat

 

[bernardgreen]

Fit an extra "bonus" socket on the other side of the wall. Even if you never use it it saves making good the un-wanted hole.