Cutting outlet holes in plaster/wood-lath walls.


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.
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roto zip tool or similar

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I remember the first time I had a project that involved cutting into the plaster walls. As I had a fairly large area to remove I thought a circular saw was the way to go. I was really surprised when I touched the saw to the plaster and it generated a rooster tail of sparks! Didn't cut it very well either. That plaster is quite cement-like (at least mine is). Since then I have used a sabre saw or a reciprocating saw a few times, but as you say it is problematic in terms of cracking, knocking the lath around, etc. It is also likely to break off the "keys" that hold the plaster to the lath, leading to problems later as the plaster gradually develops waves or bulges. Also, after a few minutes the teeth on the saw blade are not just dull, they're gone. You could try a rotozip. Bit life might be an issue if your plaster is like mine.
When I need to cut the plaster now I use a a low-tech method: carbide scribing tool (normally used for scoring cement board for tile backing.) The scribing tool can be found in the tile section of a big- box store for about $10. You just drag it along the line you want to cut, a few passes will score all the way through the plaster. You could probably then just pull out the piece of plaster you want to remove and then cut the lath with a rotozip.
--


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Cutting into wood lathe and plaster is never fun. I have always warned the customer that there may be collateral damage. One thing that I do is put two inch masking tape around the hole before I begin to cut to help keep the plaster from breaking off on the surface. Unfortunately once you fully cut the center lathe it is completely unsupported and leaves that portion of the wall susceptible to future cracking.
I have thought of possibly cutting out a portion of the center and upper or lower lathe. Then insert another vertical piece of lathe off to the side and screwing through the wall to tie it into the upper, center, and lower pieces of lathe. In theory this would keep the existing lathe stable. I have never tried this though, but if you do please post back with your results.
As someone else mentioned, I also score the plaster, but I have been using a razor knife which dulls the blade quickly. The carbide scribing tool sounds like a good idea instead.
You can try a Rotozip. I think that they make carbide bits for plaster. The high speed bit may cut through with less vibration than the forth and back motion of a hand saw.
For round holes for ceiling fixture boxes I have used a 4" carbide tipped hole saw with very good results.
I have been fortunate lately in that many of my customers with wood lathe and plaster have decided to remove it all. It makes it easier for plumbing, electrical, heating/air conditioning, insulation, and to find and repair structural problems.
Makita used to make a small diameter cordless circular saw and diamond tipped blades to go with it. I haven't looked at their product line lately to see if it is still available. I have one and used it on bigger holes for bath fans and such. It does a nice job, but there is a tremendous amount of dust as a result
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I use a carbide bit in a roto-tool. I cut through the plaster, but not the lath with it. Then pop the plaster out. I then cut the lath with a keyhole saw, drilling starter holes as needed first.
Bob
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BETAC-T wrote:

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.
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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
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volts500 wrote:

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
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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




"BETAC-T" < snipped-for-privacy@betabcghfd.cbd> wrote in message
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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.

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You can always run a screw into the lath to hold it, through any kind of block or structure you can conceive to stabilize it.
Bob
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You need something with a high speed rotary blade to minimize the back and forth yanking of a reciprcating tool.Iin a pinch a die grinder with a cut off wheel would probably work but something with saw teeth would work more efficiently.
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wrote:

THey do sell small circular saw blades for dremel tools. I never tried them, and I wonder how long they would last from plaster. Probably not long.
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