Surface box over flush

[Mkmly]

Hi
New member here. I am a multi-trades person dealing with commercial property maintenance. I’ve joined because I have some queries that can only be answered by pros - and I hope to be able to provide a few answers.
First up: I have a flush fitted back box in dry wall. I need to run new cables from this box to an area of solid wall. Best option is to change to surface mount- is it possible to mount a surface mounted box on top of the flush- using extra long screws to catch the holes in the existing dry-wall box?
I’ve attempteed it but the whole thing is a bit wobbly- not tightening up satisfactorily and in danger of cracking the switch plate. Is this a done thing or should I just fill the hole and start again?

 

[Deleted member 26818]

Depending on the make of the new double box, it’s possible to knock out the brass threaded inserts to allow extra long screws to pass through into the existing box.
If the threaded inserts cannot be knocked out, then running a 4mm drill through to remove the threads should work.

 

[SparkyChick]

I think it depends on the box you are using. I believe MK can do this with holes already present in the rear of the box. If you're stuggling to tighten it up so it's secure, use the back box screws into the dry lining box just to hold that box in place and add a couple of wall dogs to provide actual fixing of the surface mount box. Or, if you want something sturdier, use some plasterboard fixings (the screw in aluminium slugs with self-tappers or the pop out clips that you push through a 12-13mm hole).

Edit:- Re-reading the OP, scratch this as it looks like a single gang box on a single gang box.

 

[Deleted member 26818]

If the existing box is single, then use a double surface mount box.
The double boxes have holes in the back to allow 3.5mm screws to be used to fix to the single box.

 

[Pete999]

Take the dry liner box out and sling it away:
Get some timber, about 3 times the width of the dry liner box, drill a hole large enough to take the existing cables, insert the timber into the hole, feed the cable through the hole, push the timber completely into the void in the wall, fix the timber to the inside of the void with dry wall screws, fix your new surface box over the hole, by using the now fitted tmber backing, fit your switch, socke what ever it is, fill any hoes including the dry wall screw holes, repaint, go for a well earned cuppa.

 

[Mkmly]

Depending on the make of the new double box, it’s possible to knock out the brass threaded inserts to allow extra long screws to pass through into the existing box.
If the threaded inserts cannot be knocked out, then running a 4mm drill through to remove the threads should work.

Yes, the surface box does have holes all the way through and you're right, it's the two sets of threads fighting each other - I just need to catch the threads in the dry-wall box and crank it all up together. I'll strip the threads out in the second box, cheers.

 

[Mkmly]

Take the dry liner box out and sling it away:
Get some timber, about 3 times the width of the dry liner box, drill a hole large enough to take the existing cables, insert the timber into the hole, feed the cable through the hole, push the timber completely into the void in the wall, fix the timber to the inside of the void with dry wall screws, fix your new surface box over the hole, by using the now fitted tmber backing, fit your switch, socke what ever it is, fill any hoes including the dry wall screw holes, repaint, go for a well earned cuppa.

Cheers, I was thinking that might be a way to go. You're right about the well earned cuppa, jobs never seem to be as simple as you think when you first look at them.

 

[Mkmly]

If the existing box is single, then use a double surface mount box.
The double boxes have holes in the back to allow 3.5mm screws to be used to fix to the single box.

They're both double boxes - holes right through in the surface box.

 

[Mkmly]

I think it depends on the box you are using. I believe MK can do this with holes already present in the rear of the box. If you're stuggling to tighten it up so it's secure, use the back box screws into the dry lining box just to hold that box in place and add a couple of wall dogs to provide actual fixing of the surface mount box. Or, if you want something sturdier, use some plasterboard fixings (the screw in aluminium slugs with self-tappers or the pop out clips that you push through a 12-13mm hole).

Edit:- Re-reading the OP, scratch this as it looks like a single gang box on a single gang box.

It's a double box on double, I realise now that is key info.

 

[Pete999]

It's a double box on double, I realise now that is key info.

If it's double box, then the method I suggested will be easier, more room to manoeuvre.