# Installing new boxes in drywall/lath and plaster



## A Little Short (Nov 11, 2010)

I would try an old work/remodel box. If the wall is too think for the flaps to catch, you can sometimes turn the flaps around and gain some room. Next, you could use longer screws for the flaps to make even more room. If none of this works, you could just use the holes at the top and run flathead screws in. You might want a metal box for this.


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## NoBot (Oct 12, 2019)

Good advice from A Little Short. When you cut the hole for the old work box, dig a small hole first and find the wooden lathe. Only cut one lathe board, center your box on it. That way you will partially cut into the top lathe and partially into the bottom lathe board. Only fully cut one lathe board. If you cut two the plaster starts to move and fall apart.


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## jw0445 (Oct 9, 2009)

Try to find a stud and use those fiberglass? boxes that have the inside angled screws. I forget who makes them as I don't use them often


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## Dennis Alwon (May 9, 2009)

jw0445 said:


> Try to find a stud and use those fiberglass? boxes that have the inside angled screws. I forget who makes them as I don't use them often


I believe they are made by Arlington


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## wcord (Jan 23, 2011)

NoBot said:


> Good advice from A Little Short. When you cut the hole for the old work box, dig a small hole first and find the wooden lathe. Only cut one lathe board, center your box on it. That way you will partially cut into the top lathe and partially into the bottom lathe board. Only fully cut one lathe board. If you cut two the plaster starts to move and fall apart.


best to use an oscillating multi tool for that.
They don't vibrate the lath so much that the keyways break and the plaster falls off.
Of course, being covered with drywall, the plaster isn't going to fall, but its good to learn how to do this type of work.
Also, you wont splinter the remaining lath which gives you more meat for your screws.


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## oldsparky52 (Feb 25, 2020)

Did some of this in the 70's using keyhole saw. What a PITA. More than one "pop" in the plaster just a short way from the hole for the box. We used metal old work boxes and box holders (madison clips, battleships, whatever you call them). 

I found it better to use a small chisel to get the plaster out of the way before cutting the lathe boards. The plaster just killed the keyhole saw blade.


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## SummitElectric1 (Aug 8, 2016)

Some great advice above.

It's been a little while since I've had to work with plaster walls, but it was a regular task for me a few years ago when I did a lot of remodel work on historic homes.

I always used an oscillating multitool with a carbide blade for the plaster because sometimes the plaster walls in the 1930's-1940's era homes in these parts have that metal mesh (similar to the mesh used for stucco) under the plaster. The carbide blade cuts right through without catching on the metal and damaging the plaster.

@NoBot is spot on about trying to only fully cut one board of the lathe. Keeping the lathe as intact as possible will make for much better results.

@jw0445 makes a great point about finding a stud if possible. If you can locate a stud to secure the box to use a SLIDERBOX from Allied Moulded:
Allied Moulded SLIDERBOX


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## John Valdes (May 17, 2007)

Smart Box Arlington.


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## 99cents (Aug 20, 2012)

I might try F-clips, particularly if you can remove some of lathe and plaster behind and leave only drywall in the area of the F-clips. A mid size plate can cover up a lot of mess.


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## ohm it hertz (Dec 2, 2020)

Good advice all around. I use an oscillating tool with a carbide attachment that has fine teeth, and score the edge a 16th or so wider than my pencil marks. I then cut inside the relief cuts and this prevents chipping issues on trim out. Cutting the lath takes patience - I use my linesman's to secure a loose piece while cutting it to prevent vibrations and cracking. I use metal remodel boxes in varying depths and secure them with f straps and fasteners. More often than not the walls are too shallow for plastic remodel boxes, and single switches end up getting 2 gangable metal boxes for things like 3 way switching due to the shallow depth (box fill).

One benefit of drywall over lath and plaster is the added depth it buys you. You can usually use plastic remodel boxes in this instance.


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## u2slow (Jan 2, 2014)

My strategy is cut the hole as best you can, and basic metal boxes screwed to the stud from inside.

Patch the plaster with the fibrous powder mix stuff.


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## mofos be cray (Nov 14, 2016)

Nobot has the technique dialed. I use 1104LRB boxes from Iberville. F clips suck for this work because the plaster sticks out behind the lathe and holds the f clip up. Use #5 wood screws through the ears of the box into the lathe


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## Funkadelicfred (Jan 30, 2019)

Seems like the way to do it is using rework boxes and just cutting through the wall wherever makes sense.


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## hornetd (Oct 30, 2014)

Funkadelicfred said:


> Seems like the way to do it is using rework boxes and just cutting through the wall wherever makes sense.


If you're not in a tearing hurry use a dry sponge to put moderate pressure on the drywall to prevent it separating from the old plaster. Use the finer toothed metal cutting Saber Saw blades and manual handle to hold them. All reciprocating saw blades cut on pull so that is not an issue. The blades are resistant to bending and the width of the kerf makes it easier for the teeth to clear the cut on each stroke. The metal cutting blades will resist dulling by the abrasion of the plaster for longer use. Important: the blade must be fine enough to avoid vibrating the lath. If you can get close to a stud that will help limit lath separation as well. 

If you are connecting an existing Armored Cable using a metal box you may have to use Madison or F straps. Those come in different arm lengths for different thicknesses of wall sheathing. 

[RANT MODE] Caution: If you encounter metal lath you need to make certain you are not cutting into a fire wall. Fire walls are built into structures to provide time for occupants to escape, Allow the disabled to reach a place of refuge, and contain the fire long enough for manual fire suppression efforts to be applied. No old work box that I know of can be part of a listed fire wall assembly because the assemblies have not been tested for old work boxes. Only stud and bar supported boxes have been used in the testing. Even if that box will not be closely inspected have some personal ethics and cut, mount, cable, and patch the new box. Fire walls have varying duration of resistance to the passage of fire from one side to the other. Installing the wrong box type can radically shorten the fire duration it can withstand. Doing that is irresponsibly reckless! 

While I'm on the subject of Fire Walls be aware that a flush mount panel cabinet in a fire wall will often pass electrical inspection and usually fail fire inspection. You are likely to be off the job when the Fire Inspection for the Use and Occupancy permit occurs but that doesn't reduce the likelihood of a flush mounted panel board cabinet failing fire inspection. [/RANT MODE] 

Besides all that the change order to locate it elsewhere is a nice bit of time and materials work. Even if the Architect or Electrical Engineer's remedy is surface mounting you will still have to build a support rack from the floor to the building structure above that is acceptable for for support of that size and weight of electrical equipment. If the rack is not included in the change order do yourself and your employer a favor and use horizontal C channel fastened to a stud on each side of, and not behind, the cabinet to support it. Then when the Fire Inspector fails it again, because that firewall assembly is not listed to support such equipment, you can just fasten vertical C channel to the front of your horizontal pieces and presto you have a support rack. Remember that we are not the electrical engineers and it isn't within our scope of practice to review their work. If you do question their work they will often verbally tear your head off with their "who do you think you are?" superiority. 

"Theirs not to make reply, 
Theirs not to reason why, 
Theirs but to do and die, 
Into the valley of death 
rode the six hundred." 

Alfred Lord Tennyson's Charge of the Light Brigade.

--
Tom Horne


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## SPINA ELECTRIC (Dec 1, 2009)

Funkadelicfred said:


> Not a resi guy so forgive me. Want to put some rec boxes in a wall but it's drywall over lath and plaster so the wall is far too thick to mount a nailer or a gangable. What do you guys use to put boxes into a wall like that?


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## SPINA ELECTRIC (Dec 1, 2009)

If you have Romex I would use a remodel deep plastic box buy the same screws in Home Depot but about 2 inches long to expand in the lath and drywall.All I do is old work Lol I think someone mentioned this before me


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## Spencerp3 (Apr 22, 2021)

jw0445 said:


> Try to find a stud and use those fiberglass? boxes that have the inside angled screws. I forget who makes them as I don't use them often


I agree. These are by far my favorite boxes. They give the option of depth. I have only seen them at one supplier and only in plastic.


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## Djea3 (Mar 8, 2019)

Great advice about cutting in. I have been working a lot of lathe and plaster remodels lately as all pre-1970's homes in FL are plaster. Everyone knows it has been really hard to find even single gang and double gang boxes lately but I regularly use Carlon B125AB for its versatility. Flanged, nail on and horizontal/vertical screw on. It does mean finding the stud most of the time but makes life so much easier. I also can stock less types of boxes as they generally work anywhere I need a deep box. They also come in double gang B249B which saves my butt in many remodel situations. they do cost a little more and are harder to find so I try to keep them for rework or special situations.


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