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Cutting outlet holes in plaster/wood-lath walls. BETAC-T 04-09-2007
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Posted by volts500 on April 9, 2007, 7:56 pm



BETAC-T wrote:
> I have an old house with wood lath and plaster walls, and I need to cut out
> a lot holes in the walls for light switches, electrical outlet receptacles,
> etc.
>
> Here is what I am doing now, and here is what the problem is:
>
> I am just cutting them out by hand, one-by-one, using hand-held wallboard
> saws, etc. The problem is that it is hard to keep the underlying wood lath
> from vibrating and causing a wider area of plaster to crack and break out.
> I have tried making sure each hole is adjacent to one of the studs so at
> least one side of the hole has wood lath that is nailed down to the adjacent
> stud. And, I have tried being very careful, cutting out a little, reaching
> in to hold the rest of the wood lath stable, and then carefully cutting the
> wood lath. But it is still a mess, doesn't work very well, and takes a long
> time for each hole.
>
> I don't think using any kind of powered reciprocating saw or saws-all would
> help and probably would only make the lath vibrate more and damage a wider
> area of plaster than using the by-hand method.
>
> The problem seems to be the reciprocating action of the saws, so I keep
> thinking there ought to be some kind of small circular saw that could be
> used and plunged into the wall to cut the lath without vibrating it back and
> forth. But I don't have, and haven't seen, a circular-type saw that would
> be small enough to do this.
>
> I have thought about buying one of those drill bits that supposedly can saw
> sideways to cut holes in walls (which I saw on TV), but I haven't found
> anything like that in any stores and I have a hunch they don't work anyway
> (which is probably why they are only on TV).
>
> So what the heck do professional electricians do? I keep thinking they must
> have a tool or know of a trick to make this easy, especially since they
> don't want to damage their customers' walls when putting in new outlets,
> etc.
>
> Any ideas? Thanks.

Looks like you've been getting some very good advice so far. If it
makes you feel any better, my wife is good at cutting holes in lath
and plaster for electric boxes. When I re-wire old houses that have
lath and plaster, all I have to do is mark where I want a box and she
goes at it. I go to the basement and run the circuits, drill holes in
the sill plate where the boxes are going to be and stuff the cable up
into the hole. By that time she's done cutting in the holes and all I
have to do is reach in and pull out the wire.

The moral to the story is that brute force does not apply when cutting
holes in lath and plaster. Easy does it. Use sharp tools. Let the
tool do the work. Buy a couple of saws if you have to, as plaster
will dull a saw blade quick.

The trick to cutting the lath, as others have mentioned, is to _remove
the plaster first_. The trick to removing the plaster is to _score_
it first. Once the lath is exposed one can usually reach in with a
pair of lineman's pliers and grab the middle lath to hold it still
while cutting the lath. Sometimes needlenose pliers work better, or
cut out some of the lath so the lineman's pliers will fit. Go easy
towards the end of the cut. Cut as far as you have to in the upper
and lower laths, on both sides, then just snap off the lath with the
lineman's pliers.

Again, easy does it, start out slow, speed will come with practice.


Posted by BobK207 on April 9, 2007, 9:59 pm


> BETAC-T wrote:
> > I have an old house with wood lath and plaster walls, and I need to cut out
> > a lot holes in the walls for light switches, electrical outlet receptacles,
> > etc.
>
> > Here is what I am doing now, and here is what the problem is:
>
> > I am just cutting them out by hand, one-by-one, using hand-held wallboard
> > saws, etc. The problem is that it is hard to keep the underlying wood lath
> > from vibrating and causing a wider area of plaster to crack and break out.
> > I have tried making sure each hole is adjacent to one of the studs so at
> > least one side of the hole has wood lath that is nailed down to the adjacent
> > stud. And, I have tried being very careful, cutting out a little, reaching
> > in to hold the rest of the wood lath stable, and then carefully cutting the
> > wood lath. But it is still a mess, doesn't work very well, and takes a long
> > time for each hole.
>
> > I don't think using any kind of powered reciprocating saw or saws-all would
> > help and probably would only make the lath vibrate more and damage a wider
> > area of plaster than using the by-hand method.
>
> > The problem seems to be the reciprocating action of the saws, so I keep
> > thinking there ought to be some kind of small circular saw that could be
> > used and plunged into the wall to cut the lath without vibrating it back and
> > forth. But I don't have, and haven't seen, a circular-type saw that would
> > be small enough to do this.
>
> > I have thought about buying one of those drill bits that supposedly can saw
> > sideways to cut holes in walls (which I saw on TV), but I haven't found
> > anything like that in any stores and I have a hunch they don't work anyway
> > (which is probably why they are only on TV).
>
> > So what the heck do professional electricians do? I keep thinking they must
> > have a tool or know of a trick to make this easy, especially since they
> > don't want to damage their customers' walls when putting in new outlets,
> > etc.
>
> > Any ideas? Thanks.
>
> Looks like you've been getting some very good advice so far. If it
> makes you feel any better, my wife is good at cutting holes in lath
> and plaster for electric boxes. When I re-wire old houses that have
> lath and plaster, all I have to do is mark where I want a box and she
> goes at it. I go to the basement and run the circuits, drill holes in
> the sill plate where the boxes are going to be and stuff the cable up
> into the hole. By that time she's done cutting in the holes and all I
> have to do is reach in and pull out the wire.
>
> The moral to the story is that brute force does not apply when cutting
> holes in lath and plaster. Easy does it. Use sharp tools. Let the
> tool do the work. Buy a couple of saws if you have to, as plaster
> will dull a saw blade quick.
>
> The trick to cutting the lath, as others have mentioned, is to _remove
> the plaster first_. The trick to removing the plaster is to _score_
> it first. Once the lath is exposed one can usually reach in with a
> pair of lineman's pliers and grab the middle lath to hold it still
> while cutting the lath. Sometimes needlenose pliers work better, or
> cut out some of the lath so the lineman's pliers will fit. Go easy
> towards the end of the cut. Cut as far as you have to in the upper
> and lower laths, on both sides, then just snap off the lath with the
> lineman's pliers.
>
> Again, easy does it, start out slow, speed will come with practice.

BETAC-T

You've gotten good advice...esp "easy does it"

I have a 1930 house with wood lath & plaster...over the years I've
added electrical boxes.

Sawzall does not work.....too much damage. :(

A sharp keyhole saw or new Sawzall blade in their handle works as well
but you've got to be careful.

I finally settled on Dremel with diamond bit thru plaster.

Dremel with wood bit thru wood lath.

Rotating bit stresses the lath/plaster less than any other techhnique.

If the plaster is smooth (not a fancy texture, like about 1/2 my
house) after the plaster plug is removed I drill through & screw the
plaster to the wood lath.

Smooth plaster is easy to fix / match......the trick textures are a
pain.

I do one box at a time & only very occasionally.

If I were doing a large number of boxes at once I would setup a jig/
guide & screw or double back tape it to the wall

And "go to town" with two rotozips (once w/ plaster bit, one with wood
bit)

Instead of mounting a "tiger box", I glue (construction adhesive)
plywood blocks to the opposite the wall interior face & screw the box
to the blocks. Reinforces the opposite wall & doesn't stress the new
hole. I use deep boxes so I don't need much plywood.

When I'm finished, I "caulk" around the box with SIKA Sikadur
AnchorFix #1.

This stuff gels in 5 minutes, full cure in 1 hour....stronger than
concrete; bonds to plaster, wood & concrete. Fits in a standard
caulk gun

The final installation is rock solid.

cheers
Bob


Posted by volts500 on April 10, 2007, 4:35 am



volts500 wrote:

> The trick to cutting the lath, as others have mentioned, is to _remove
> the plaster first_. The trick to removing the plaster is to _score_
> it first. Once the lath is exposed one can usually reach in with a
> pair of lineman's pliers and grab the middle lath to hold it still
> while cutting the lath. Sometimes needlenose pliers work better, or
> cut out some of the lath so the lineman's pliers will fit. Go easy
> towards the end of the cut. Cut as far as you have to in the upper
> and lower laths, on both sides, then just snap off the lath with the
> lineman's pliers.

I forgot to mention when making the first cut in the lath not to cut
it all
the way through....stop it short about 1/4". That way when you are
making the second cut the lath won't flap around. Once the second
cut is made all the way through you can then snap the lath out with
your pliers or use your saw to remove the final 1/4" of lath on the
first
cut. If you use old work boxes with snap brackets, the brackets will
secure the loose middle laths when you tighten it. Here's what they
look like:
http://www.usahardware.com/inet/shop/item/30060/icn/20-339473/allied_moulded_3337/9331esc2.htm


Posted by Steve Barker on April 9, 2007, 9:58 pm


Forget the rotozip. The bit will last about a half inch. The best I've
done is with a saber saw and fine cutting metal blades. Figure on about one
blade per outlet hole. Drill a 1/2" hole at each corner, then cut between
the holes. Figure on a new paddle bit about every 15 holes. I just
finished completely rewiring a hundred year old two story, and have many
many smooth blades and worthless paddle bits to show. <G> Another option I
haven't tried is perhaps a dremel type tool with about a 2" diameter blade
on the end of it.

--
Steve Barker




>I have an old house with wood lath and plaster walls, and I need to cut out
>a lot holes in the walls for light switches, electrical outlet receptacles,
>etc.
>
> Here is what I am doing now, and here is what the problem is:
>
> I am just cutting them out by hand, one-by-one, using hand-held wallboard
> saws, etc. The problem is that it is hard to keep the underlying wood
> lath from vibrating and causing a wider area of plaster to crack and break
> out. I have tried making sure each hole is adjacent to one of the studs so
> at least one side of the hole has wood lath that is nailed down to the
> adjacent stud. And, I have tried being very careful, cutting out a
> little, reaching in to hold the rest of the wood lath stable, and then
> carefully cutting the wood lath. But it is still a mess, doesn't work
> very well, and takes a long time for each hole.
>
> I don't think using any kind of powered reciprocating saw or saws-all
> would help and probably would only make the lath vibrate more and damage a
> wider area of plaster than using the by-hand method.
>
> The problem seems to be the reciprocating action of the saws, so I keep
> thinking there ought to be some kind of small circular saw that could be
> used and plunged into the wall to cut the lath without vibrating it back
> and forth. But I don't have, and haven't seen, a circular-type saw that
> would be small enough to do this.
>
> I have thought about buying one of those drill bits that supposedly can
> saw sideways to cut holes in walls (which I saw on TV), but I haven't
> found anything like that in any stores and I have a hunch they don't work
> anyway (which is probably why they are only on TV).
>
> So what the heck do professional electricians do? I keep thinking they
> must have a tool or know of a trick to make this easy, especially since
> they don't want to damage their customers' walls when putting in new
> outlets, etc.
>
> Any ideas? Thanks.
>



Posted by BETAC-T on April 10, 2007, 2:59 pm


Thanks everyone for all of the great ideas and suggestions. Since so many
people described the same kinds of issues I have been encountering, at least
I know it's not just me -- it's not a job with a known clear-cut easy
solution.

I have been cutting out the plaster first (by scribing it, etc.), and then
working on the wood lath. So, at least I have that part figured out. And,
I have been trying to work VERY slowly and VERY carefully, but it's still a
pain.

I looked up "Rotozip" because, to be honest, I didn't really know what that
was. Seems like it uses the "side-cutting" drill bit concept I had seen on
TV. And, I guess it has some types of small circular blades that may help
in cutting the laths. I'm definitely going to Home Depot, Lowe's etc. and
checking them out today.

There's a subject heading called "Rotozip: goodgawd..." that was posted in
this newsgroup on 04/09/2007 at 11:45 PM that has some additional info and
thoughts about Rotozips.

Yesterday, I started thinking there ought to be some kind of jig or clamp
that I could use (or invent) to clamp the lath tight while cutting it to
keep it from vibrating. I thought maybe there is a way to cut out the
plaster part (that's easy), then slip the clamping device between the space
between two laths, then tighten it down to clamp the laths from the back up
tight against a flat piece that is on the wall surface -- then cut the
laths. I didn't see any ready-made clamping devices that would do that, but
I'm sure someone here can come up with that invention. I am just surprised
that electrician's don't already have something like that that they use.
The best I could figure out for now was to try buying a 5-inch metal
90-degree angle brace. I don't know if that will work, but I'm going to see
if there is a way to use that to put through the space between two laths and
pull them tight from the back while cutting. Right now, I can't picture
that working in my mind. But, I'll bet there is something along those lines
that could be created or fashioned to do what is needed.

Thanks again to everyone.


>I have an old house with wood lath and plaster walls, and I need to cut out
>a lot holes in the walls for light switches, electrical outlet receptacles,
>etc. ............



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