Do you have a Rotozip with the Zipmate attachment? I have used that with a metal cut-off wheel to cut through plaster. I use the metal wheel since it is thinner than the masonry wheel. It seems to work pretty good. I then use a jig saw or a wood zip bit to cut through the wood lathes.

Someone may have a better idea than this, but this has worked for me really well putting outlet boxes in plaster walls. I don't like to use the plaster bits that they sell for the Rotozip. They seem to overheat and they don't cut through wood very good at all.

I don't have a rotozip but maybe I could borrow one. Does it work sort of like a dremel tool?

I was trying to do cheap fixes to the bathroom (re-painting the painted-over plastic tiles, new towel racks) but as usual that was a silly notion!

Thanks for your response. I like the idea of working my way through the layers. :)

"I don't have a rotozip but maybe I could borrow one. Does it work sort of like a dremel tool?"

It is a dremel tool on steroids, with a depth adjustment.

It will go through the plaster easily, then you can cut the wood lathe.

The zip tool can also cut wood, but you have to move at the correct cutting speed to avoid burning up the bits.

Be careful cutting the lath to not break the 'keys' (where the plaster sticks through the gaps in the lathe) holding the plaster to the lath.

How about using an old fashioned rasp, since the amount of material you have to remove now is so small? I've seen my DH do that sometimes (although we didn't have to deal with the plastic tile). It would be slow, but could be very incremental. You sure wouldn't want to remove too much and have the hole be too big!

Thanks for all the tips. I'll look into the rotozip.

BTW, the plaster is mixed with sand I think. It's a lot like cement! At one point I found it easier to knock out a stubborn chunk with a hammer than to saw it. I have a newfound appreciation for the durability of these old walls!

Kim, I actually tried a rasp but since the lath has been cut it's unstable and moved, and the plastic tiles responded by chipping unevenly. But it did seem like something worth trying.

This is the most frustrating 1/8" I've ever encountered!

4" grinder is terrific for this kind of cut; terrifically dusty, too.
Casey

"4" grinder is terrific for this kind of cut..."

Just not for the inexperienced when it grabs and kicks back.

Adjective "terrific" cuts both ways!
Casey

I was too scared of the grinder, so went with the Rotozip which cut through the plastic tiles OK, but got really gummed up with the adhesive under the tiles and actually sparked in the plaster (flecks of sand?). Ended up chipping away the plaster with the claw of a hammer and then going back to the jigsaw for the lath (the rotozip seemed to be burning it).

Anyway, the deed was done. Thanks everyone for your advice!