What sort of electrical box to use?

[Jeff]

Hi All,

I've got to put a fan isolator switch into a plaster and lath wall. So what sort of box should I use, dry lining or metal KO flush box? as I don't want to use a surface mount box.

Thanks,

Jeff

[usenet]

I don't think it matters really, it's probably easier to mount the metal one properly as the dry lining ones are designed to clip into plasterboard and I don't quite see how you'd fix one into a lath and plaster wall. So, on reflection, I think you ought to use a metal box.

[Jeff]

Cheers Chris.

Jeff

[Christian McArdle]

I concur. The lath and plaster has always been too thick and variable to take a dry lining box when I've tried. You need to install a batten behind to fix a metal unit to, or channel out a stud to the depth of the box. For light switches, in the past I've managed to install a small wooden plate attached to one stud only to avoid having to make a large hole. I'm not sure if this would be suitable for sockets, though, where you have to apply much pressure against the accessory to insert the plug and you don't have much depth to get a strong connection between plate and stud.

Christian.

[Dave Plowman]

I doubt you'll get a fixing with a dry lining box in a lath and plaster wall.

My way would be to cut out the hole in the wall, then fix a couple of vertical battens slightly longer than the hole from say 1 x 1/2" on the back of the laths securing with brass screws (steel ones will rust and pop the plaster) through from the outside. Then drill suitable holes in the backing boxes and fix to these battens. After making good with a one coat plaster you'll have a fixing that's as strong as the wall.

Or if you're lucky and the box position falls between two complete laths, you can sometimes 'tosh' thing screws into those laths through holes you've drilled in the boxes.

However, the first method is guaranteed to give a solid fixing.

[Jeff]

Cheers everyone for your advice,

I'm in the middle of renovating our bathroom, this involves a new bathroom suite and redocorating the whole thing. This meant taking all the tiles off (the whole bathroom is tiled floor to ceiling) whilst doing this most of the plaster came down as well.

So whilst speaking to my plasterer I hit upon the idea of taking the laths down on the inside of the bathroom and he'd put up plasterboard a) it'll be quicker for him (cheaper for me!) b) I can fix all the pipe work for the shower and electrics and re-route the light switch to outside the bathroom, far more easily than channelling into the walls.

So I should be able to fix a couple of battens from the inside of the bathroom and then sink the box from the outside.

Jeff

BTW good point about the brass screws, could you use galvanised screws instead?

[BigWallop]

If you cut just the plaster with a sharp (Stanley) knife to the size of box you're going to use (use the box as a template), then you'll be able to see where the laths are. Take a sharp knife or small pad saw (hacksaw blade without handle) and cut out the laths to the same size. Try to stop the laths separating from the surrounding plaster. Slip a piece of inch by inch, or inch by inch 'a' half, into the hole that you can turn upright (vertically) like a stud, and fix it in the middle of the hole with long screws right through the plaster and remaining laths, above and below the hole. Bury the heads of the fixing screws just below the surface of the plaster so that when the holes are filled they disappear. You should then have a solid enough timber to fix a box to.

One tip is to screw a nail into the middle of the wooden strap you're using and tie a piece of string to it. This helps to stop you losing it down inside the wall and gives you something to pull against when you're putting the fixing screws in.

[usenet]

Why not use stainless?

[Dave Liquorice]

Be *very* *very* careful. I still haven't got proper feeling back in the top 1/2" of my 2nd finger left hand and a "funny" patch on the

3rd, after attempting to amuptate them whilst cutting a hole in plasterboard with a "sharp (Stanley) knife". This was about 3 1/2 years ago.

Best approach is to drill a hole and use a pad saw of some description to cut and enlarged the hole as required. It is easyier and safer.

It was trying to stop the plasterboard wagging about with lefthand that got it the wrong side of the "sharp (Stanley) knife"...

It might need a notch to take the box, depending in the thickness of the lath/plaster and the depth of the box. I should think trying to squeeze the cables for a fan in a 15mm box a bit tight. But a good method.

[Charles Lamont]

Amazing, I was doing this very job this afternoon. I was surprised just how well a knife goes through this lime plaster. For sawing the laths use a fine-toothed blade the wrong way round, so that it cuts on the pull stroke, Japanese style.

Just-in-time advice. Ta.