Deep back box into lath and plaster

[ismellburning]

Hello all,

I'm installing new light switches throughout my Victorian house.

All the walls are lath and plaster, which as you might expect, has gone off fairly dramatically and is now fairly brittle and crumbly.

My new light switches are a tad deeper than the old ones, and as such don't fit into the 16mm back boxes that are already in the wall.

I'm installing deeper (35mm if I recall) back boxes, which is obviously too deep to sit flush with the plaster surface without cutting through the lath.

With the lath cut through there's nothing to attach the back box to, which means it falls into the wall at the first application of pressure.

My current plan is to screw a length of wood to the back box that will brace the back box against the other side of the cavity. Obviously the other end of the wood won't be permanently attached to the wall, but once the front plate is screwed on to the back box and made good with plaster I expect it to be solid. I've heard tales of people finding back boxes braced with wodges of newspaper/bunched up plastic bags, so I'm expecting this to be adequate.

Am I wrong in that expectation? All dissenting/affirming voices welcome!

Cheers!

 

[ban-all-sheds]

//search.diynot.com/forum_sear...tbytime=0&author=&search=Search+Forum&stype=0

 

[Taylortwocities]

Its not easy. If the plaster is in reasonable condition, then use a plunge saw, like a Bosch / Festool and fit a dryliner box. It should clip onto the laths OK.

 

[ismellburning]

Ta muchly, & cheers for the link, appreciated.

I like the idea of drywall boxes but suspect that my first, er, effort at getting the backbox in has produced a hole that will be quite tricky to clip a box into.

Will attempt bracing it from the back, per a few of the replies in the search results.

Ta again

 

[JohnW2]

I like the idea of drywall boxes but suspect that my first, er, effort at getting the backbox in has produced a hole that will be quite tricky to clip a box into.

You may have to consider making the hole slightly bigger (not necessarily neatly), then remove plaster (but not laths) from the surrounding area, repair the area with plasterboard (and plaster) and then put a dry lining box through a hole in the plasterboard ... I've had to do that a good few times! IME, Victorian lath+plaster is often too thick (not the least because the laths are often not flat) for dry lining boxes to clip onto it satisfactorily.

Kind Regards, John

 

[ismellburning]

You may have to consider making the hole slightly bigger (not necessarily neatly)

Believe me, the 'neatly' ship has well and truly sailed

Will consider my options.

 

[JohnW2]

Believe me, the 'neatly' ship has well and truly sailed Will consider my options.

Don't feel bad - making neat holes in old lath+plaster can be next-to-impossible. The laths are often quite hard, and the plaster (which often resembles sand!**) simply crumbles away when one tries to cut through the laths - hence the not uncommon need to have to resort to the sort of approach I outlined. Putting in wooden noggins and attaching metal boxes to them is not really an answer, either, since it can then be very difficult to satisfactorily repair the plaster up to the edge of the box. With a bit of inset plasterboard, at least one then has a fairly easy situation to deal with.

[** there are two types of plaster in the Victorian parts of my house - one type resembles sand, and the other resembles an incredibly hard type of concrete - and both are 'a problem'!]

Kind Regards, John

 

[ismellburning]

making neat holes in old lath+plaster can be next-to-impossible.

Very relieving to hear that!

Might try bracing and plaster repair for now as smallest size plasterboard is waaaay too big for the hole I've got and I'd have to either store or chuck the leftover. Roll on the bigger wall jobs next year though

Thanks man, nice to meet another lath and plaster sympathiser *coughs up cloud of plaster dust*

 

[JohnW2]

Might try bracing and plaster repair for now as smallest size plasterboard is waaaay too big for the hole I've got and I'd have to either store or chuck the leftover. Roll on the bigger wall jobs next year though

Good luck. I'm not sure that I understand how your 'bracing' approach is going to work, since there will be remarkably little (if I understand you correctly, basically just a little plaster around the edge of the box) holding the box in place. At the least you probably will need to attach the wooden block to something - dare I suggest that you might end up looking to the infamous expanding PU foam (better than screwed up newspaper!)?!

You can get quite small sheets of plasterboard - certainly around 2x4 feet. If you have several boxes to do, it might be worth investing maybe £4!

Kind Regards, John

 

[ismellburning]

Not sure I've explained the bracing concept very well. Imagine a back box wedged in place from behind by some screwed up newspaper. Now replace that newspaper with a piece of wood. It's to stop the backbox moving backwards into the wall when the face plate gets pushed on.

May not work, of course, but the beauty of a house with knackered walls (and a patient wife) is that experimentation is permitted

Will look up smaller bits of plasterboard as well.

 

[JohnW2]

Not sure I've explained the bracing concept very well. Imagine a back box wedged in place from behind by some screwed up newspaper. Now replace that newspaper with a piece of wood. It's to stop the backbox moving backwards into the wall when the face plate gets pushed on.

I understood that much - but what is stopping the box (and face plate) moving forwards (i.e. out of the wall)? As I understand it, the plaster around the edge of the box would be the only thing that would be doing that - and it might not last very long when the switch was being 'handled'. With a switch, you might get away with it - for a socket, it would almost certainly be a disaster, since the whole lot would probably come out of the wall when one tried to pull a plug out! As I said, 'sticking' your wooden block to the laths on the other side of the wall (maybe with PU foam) might be one approach to consider.

Kind Regards, John

 

[ismellburning]

Oh I see. You make an excellent point, especially re boxes that will get rougher treatment like sockets.

Another trip to the shops in the offing it seems. Thanks for advice, 'tis appreciated.

 

[JohnW2]

Oh I see. You make an excellent point, especially re boxes that will get rougher treatment like sockets. Another trip to the shops in the offing it seems. Thanks for advice, 'tis appreciated.

You're welcome. As you will realise, I've "been there" myself on many an occasion. Whilst there's probably no perfect solution, I've plenty of experience of some of the approaches (some of which are reasonable, others are not!).

Kind Regards, John

 

[ban-all-sheds]

How many switches and sockets are there to do?

How close are they, typically (least, most) from the studs? (which are how far apart?)

What else will you/might you be fixing to/doing to the walls?

Does the L&P have any architectural merit?

Are these words starting to rearrange themselves the more you contemplate the future:

bullet the later bite going plasterboard with sooner or to have to

?

 

[ismellburning]

bullet the later bite going plasterboard with sooner or to have to

Ha! Suspect you're right but the wall's a big un and it seems like I'd have to do quite a big bit of plasterboard to make the mess worth it. Seems like overkill for a wall with a single, one-gang light switch on it

Broadly though yes, a lot of the walls have blown plaster which is alarming to lean against (squashy walls not normal as far as I know) and impossibly to hang things on without accidentally smashing massive holes in so yes, plasterboard armegeddon is in the offing.

But trying to keep things small scale for light switches