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#193578 - 04/08/10 03:16 PM Plaster and Lathe  
mr_electrician  Offline
Member
Joined: Jun 2007
Posts: 106
London, Ontario
Hi, I have to install a octagon box for a light in an old house that has lathe and plaster. As many of you know it is tricky to deal with this when making cuts as it likes to fall apart. I need to cut a strip out so I can run my wiring through the ceiling joist from the light switch (second floor above, no attic). Is there any techniques you guys have that make cutting this stuff out any easier or less messy?


Never trust an electrician with no eyebrows!!

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#193580 - 04/08/10 03:59 PM Re: Plaster and Lathe [Re: mr_electrician]  
EV607797  Offline
Member
Joined: Oct 2006
Posts: 745
Fredericksburg, VA, USA
I use a carbide-tipped hole saw at low speed and minimal pressure.


---Ed---

"But the guy at Home Depot said it would work."

#193593 - 04/08/10 10:35 PM Re: Plaster and Lathe [Re: EV607797]  
Rewire  Offline
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Joined: Feb 2008
Posts: 165
Missouri
a one gallon shop vac to suck up the dust


#193726 - 04/15/10 09:05 PM Re: Plaster and Lathe [Re: Rewire]  
jimbob  Offline
Member
Joined: Dec 2009
Posts: 15
Canada
try to get close to a ceiling rafter and when cutting through old plaster i find running the hole saw in reverse there is less chance that the plaster will fall down.if plaster is really bad and thin i will pencel out a pancake box score it with an exato knife untill plaster falls away from wooden laths and use inch 10 wood screws to fasten to ceiling.As for running from switch to light try to find out which way ceiling joist are running ,notch out in corner of ceiling and wall fish down wall into basement and up to switch location. good luck.


#193733 - 04/16/10 10:18 AM Re: Plaster and Lathe [Re: jimbob]  
mr_electrician  Offline
Member
Joined: Jun 2007
Posts: 106
London, Ontario
Originally Posted by jimbob
try to get close to a ceiling rafter and when cutting through old plaster i find running the hole saw in reverse there is less chance that the plaster will fall down.if plaster is really bad and thin i will pencel out a pancake box score it with an exato knife untill plaster falls away from wooden laths and use inch 10 wood screws to fasten to ceiling.As for running from switch to light try to find out which way ceiling joist are running ,notch out in corner of ceiling and wall fish down wall into basement and up to switch location. good luck.


Thanks for that tip. I am not sure of screwing a pancake box to the lathe will be suffice though. I plan on cutting out enough of the plaster and lathe where the box will be so I can use a bar hanger. The customer wants to hang a pretty heavy light!


Never trust an electrician with no eyebrows!!

#193741 - 04/17/10 05:04 AM Re: Plaster and Lathe [Re: mr_electrician]  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
We have a ton of older houses over here in NZ, that still have the lath and plaster walls and ceilings.
Over the years, I've tried various methods to cut that stuff, with widely varying results. crazy
I think the key to cutting this stuff, without tears, is to use a tool that will cut quickly with the minimum of vibration to the surrounding laths, that is what will cause things to turn to custard in a real hurry.
I have used a Dremel tool with a cutting disc in it before today to cut out "flush-box" holes in walls, for new sockets and light switches.

I have also used, at a pinch, a 4" grinder with a cut-off disc in it too, just make sure you ascertain where any timber joists are behind the laths, before you start cutting, marking your final cut in pencil gives you a good guide.
One thing needs to be said here, if you are going to be using power tools like this to do the cutting, you'd better have very good control of said tool, otherwise you could find it sailing across the wall or ceiling all of a sudden.
Not a good look.

One bit of advice I got from a guy I served my time with and have never forgotten is, if you have to make a hole in anything, always start small, filler is cheap, this also allows you to "move" your hole around to a certain degree, if it is slightly in the wrong place, making a big hole for a start, helps no-one and costs us money and time to get it fixed.

Last edited by Trumpy; 04/17/10 05:05 AM. Reason: Typo

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