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I have cut a hole into an old lath-and-plaster wall for an electrical switch.

I used a drill, followed by a drywall saw. Despite being very slow and careful, the lath is now loose from the plaster. This is how it looks:

enter image description here

Unfortunately the hole is not big enough and I need to saw off a little bit more. I try to push the lath to the plaster while sawing to minimize movement but I am afraid it gets too unstable and plaster will break.

How do I best stabilize lath and plaster to avoid more damage?

How shall I proceed to enlargen the hole?

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  • What tool(s) have you used so far to cut this hole? How were electrical boxes inset into lathe and plaster walls in original construction? Originally switches and receptacles must have been surface mounted to lathe and plaster, but at some point they were inset into these walls. So how did real craftsmen open up a wall to install an electrical box?
    – Jim Stewart
    Jul 22 at 10:44
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    What power tools do you have available? Something like a jigsaw with a blade that cuts on the "pull" stroke should work there.
    – brhans
    Jul 22 at 12:40

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Use a chisel or nibbler or other such too to break off the plaster to the size you want, bit by bit, then use an oscillating tool to cut off the exposed lath.

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    I’d even sacrifice a blade and use the oscillating tool for the plaster as well.
    – Aloysius Defenestrate
    Jul 22 at 13:10
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    Abrasive particle blades for oscillating tools are a thing too. They work on plaster.
    – MTA
    Jul 22 at 13:52
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    Temporarily shoving in a small piece of 2x4 to "back up" the cut might be worth considering. If it gets lost in the wall, shrug...
    – keshlam
    Jul 22 at 15:21
  • The reason I hesitate to use the oscillating tool on the plaster part is that it can be fragile, and the vibration might cause a crack where it may not be desired.
    – Huesmann
    Jul 23 at 11:58
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    @Huesmann exactly this was the background for my question. I have tried with a proper carbide blade and I feel the oscillating tool is better (less vibrations) than anything else I tried (reciprocating saw, handsaw, drywall saw).
    – divB
    Aug 6 at 7:05

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