1930s walls, flush fitting electrial boxes

[choppachimp]

so I read up on the pros and cons on these very pages. I invest in enough cutting equipment to put a second channel tunnel in place The Screwfix catalogue becomes my bible and I order 35mm metal back boxes like they are going out of fashion, so I can get the wires in without a struggle. As I engulf the house in a blizzard of dust I make a new discovery...

I dont have SOLID walls!

what I appear to have is a heavy concrete like plaster of about 5mm on top of a cream coloured soft stone second layer, about 7-8mm and then I have a cavity.

In short I've got nothing to screw the metal boxes to!

HOW DO YOU FIX TO SUCH A WALL?

I've tried a couple of dry lining plastic boxes but the ears arent deep enuff to fit behind 13mm of remaining surface?

do I tack/pin the metal boxes to the stone surfaces I can see? should I use something a little less violent than the SDS Plus and socket sinker kit? (as it destroys most of the surrounding outter layer in the process)

yours <cough> dusty & frustrated

 

[masona]

Don't how the expert do it but I have done one with screw & rawlplug into the side.

Edit: Just re-read your post, are you saying you have approx 12mm thickness wall?

It's not plaster & lath is it?

 

[choppachimp]

yes approx 13mm thick, its made of two layers, one a thick concrete like plaster and the second a kinda brick....its as though the stud structure, typically made of timber, is in fact formed of cream coloured blocks if that makes sense?



Just looking at Lath & Plaster of Wiki: http://en.wikipedia.org/wiki/Lath_and_plaster cant be 100 per cent sure its like that, I've not seen it from the other side I'll try and get a picture of one of the holes I punched through for the light switch.

 

[ELZ4742]

could just grip fill/cement em in

 

[choppachimp]

could just grip fill/cement em in

really? I considered this....bascially punch the hole, make good with cement and then set the metal box in them? or should I switch to a plastic that has a slight rim to the front?

 

[davy_owen_88]

Go with the metal boxes and just press them into the cement. If you remove a few extra knock-outs before pressing it in then the cement will fill around these locking it in place. Remember to remove the excess cement though

 

[ELZ4742]

makes no odds, metal or plastic. obviously the only downside is that once its in, its a pain in the arse to move so make sure you have all your levels correct.

 

[ELZ4742]

makes no odds, metal or plastic. obviously the only downside is that once its in, its a pain in the arse to move so make sure you have all your levels correct.

 

[choppachimp]

cheers folks, seems to make sense about setting into wet cement...

Reading up on this Lath thing, could it be I have horse hair and lime plaster? on some sort of lath....did keep finding bits of what looked like wood/hair like in the broken plaster and surrounds

 

[bernardgreen]

makes no odds, metal or plastic. obviously the only downside is that once its in, its a pain in the a**e to move so make sure you have all your levels correct.

To hold the box in place while the cement sets use a strip of wood (or plastic ) 10 inches or so long, an inch wide and 1/4 inch thick. Drill two holes either side of the centre of the to match the plate fixing holes in the back box and fit the wood to the box useing screws from socket. Press the box into the hole and either tape or tack the ends of the wood to the wall once the box is in the right place and level.

 

[Nige F]

Cream coloured hollow clay blocks ....circa 1930

 

[choppachimp]

Cream coloured hollow clay blocks ....circa 1930

wouldnt have any links to pics or text on these Nige? must say it fits with what I've seen. I'm gonna try and expose the two layers tonight and see if I can photo it