45A Cooker Switch - Back Box Size & Filler

[sjw64]

Hi

Im replacing my current 45A Coooker Switch for a nicer looking one and at the same time refitting my entire kitchen.

When I have removed the metal back box a load of brick has crumbled away leaving a fair bit of space to be filled in with something to support the metal box.

What can I use to fill the space and what size back box do I need (35mm?) (I want to pick one up from ScrewFix on my way home today)

 

[PrenticeBoyofDerry]

47mm backbox for the standard cooker isolator switch.
I generally use plasterboard dry-line adhesive to fill in voids/gaps in walls.
It sets rock hard, the boxes can be left to set in them and the compound allows you to put a fixing in it.
Others may use
*sand/cement mixture
*bonding coat
*plaster/cement/sand mixture
*expanding foam

 

[sjw64]

Excellent ..thanks just what I was after.

The crumbled brickwork has almost gone through to the next room (room under stairs) so Im going to have to fix a backing board on to that wall to stop the filler/plaster/cement/etc from dropping thru it. literally daylight!

 

[PrenticeBoyofDerry]

If you remove all the loose stuff, then on reverse side of wall (under stairs] cut a wee bit of plasterboard to fit the hole. Apply board adhesive on the internal of hole, so you can insert plasterboard so slightly recessed, 2-3mm on this wall. Have a good dollop of the adhesive on board within hole and wall, so board and wall will adhere. Leave for the manufactures specified time to set (usually a couple of hours).
Then you can fill in the hole on the socket side, if your canny you can set the backbox within the compound, but make sure you have it exactly were it is to stay as it will not budge once set, so ideally isolate circuit, grommet backbox and feed cable through. Then insert backbox into compound to set. Once set I would leave overnight, you can tidy up around backbox, pilot for wall plugs, insert plug and screw up.
The adhesive, will set rock hard, and if backbox is left to set in it, the need for screws would be unlikely but belt/braces.
Leaving 2-3mm on reverse side of wall, will allow you to plaster that flat with existing wall.

 

[JohnW2]

The crumbled brickwork has almost gone through to the next room (room under stairs) so Im going to have to fix a backing board on to that wall to stop the filler/plaster/cement/etc from dropping thru it. literally daylight!

How thick is this wall - is it just a single brick thickness? If so, and if we are talking of a 47mm back box, you might theoretically run foul of the regulations about how deep a hole (proportion of wall thickness) is permitted in a wall - if that matters to you!

Kind Regards, John

 

[sjw64]

The crumbled brickwork has almost gone through to the next room (room under stairs) so Im going to have to fix a backing board on to that wall to stop the filler/plaster/cement/etc from dropping thru it. literally daylight!

How thick is this wall - is it just a single brick thickness? If so, and if we are talking of a 47mm back box, you might theoretically run foul of the regulations about how deep a hole (proportion of wall thickness) is permitted in a wall - if that matters to you!

Kind Regards, John

Good point. I think its single, I'll have to check when I get home tonight. I'll check the size of the current back box as well.

 

[EFLImpudence]

Surely it's only chases which are regulated.

A hole doesn't matter.

 

[JohnW2]

Surely it's only chases which are regulated. A hole doesn't matter.

Hmmm - definitions again! What's a hole for a back box if not a 'short and wide chase' - or is there a definition of 'chase' which requires a minimum length? The structural integrity of a wall presumably doesn't care what one calls the deficiency one has created in it!

Having said that, I can't remember what the reg actually says - do you know?

Kind Regards, John

 

[EFLImpudence]

A horizontal chase of some length and more than one sixth depth could potentially lead to the wall collapsing because, obviously there is nothing holding it up.

Making a hole or removing a whole brick has no effect.

Anyway, the hole is already there.

 

[JohnW2]

A horizontal chase of some length and more than one sixth depth could potentially lead to the wall collapsing because, obviously there is nothing holding it up. Making a hole or removing a whole brick has no effect.

That's obviously total common sense, so maybe there should be a minimum length of 'chase' below which it can be as deep as one wishes. However, FWIW I've just looked at Approved Doc A, and it does not seem to define 'chase' - so I guess one has to work to a definition of one's own invention.

Anyway, the hole is already there.

True, but it's going to be at least partially repaired.

As I said when I raised the issue, it's only relevent if "it matters to the OP"!

Kind Regards, John

 

[mfarrow]

The risk is the wall coming down if you chase across its entirety, or you compromomise a butress by vertical chasing.

I've taken whole bricks out before, I'm pretty sure it didn't compromise the wall! And a back box for a cooker switch is <1/2 brick width.

I believe Approved Document A talks about openings <0.6 from corners/buttresses not being automatically permitted. If this is the case here you might want to consult a structural engineer to do some calculations for you. Or not.

 

[sjw64]

Thanks for all the replies. Here are some photo's of the dilemma Im faced with. Ive taken as much as the loose stuff out as I can and there is a whopping big hole.

Its a single brick wall. Any suggestions?

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• sjw64
• 4 Apr 2014
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• 4 Apr 2014
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• sjw64
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[EFLImpudence]

Any suggestions?

Already given.

It's nothing out of the ordinary.

 

[GaryGarden]

Do both the cables in the conduits connect to the supply side of the cooker switch? It appears to be a ring!
What is the FCU serving, the hob?

 

[sjw64]

Do both the cables in the conduits connect to the supply side of the cooker switch? It appears to be a ring!
What is the FCU serving, the hob?

Both the cables go into the back of the socket box. One comes from the fuse box under the stairs and the other cable goes to the oven & hob. The small socket (FCU?) feeds the fan extractor