# Advice on opening many ceiling holes for recessed light in rock lath and plaster



## gottalearn (Oct 30, 2014)

Not sure if this is better asked here or over at electrical


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## joecaption (Nov 30, 2011)

Any Lowes or Home Depot sells a grit hole saw just for this. (often in the lighting area)
Seems like mine are something like Remline brand, there green.
Replace the 1/4 twist drill pilot drill with a masonry bit. 
There a special size made for recessed lights.
Once the hole saw goes through the plaster and backer I stop and use a regular hole saw to get through the lath.
A Key hole, sheetrock saw, sawsall even with a carbide blade will just make a mess.
A simple trick I do is buy one of those cheap plastic pans for setting under plant pots to slip over the arbor to catch most of the dust.
The trick to go up in the attic first to figure where the joist are. 
Ideally you want those cans in the middle of the joist bays.


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## Colbyt (Jan 27, 2014)

Rock lathe is the drywall like stuff isn't it?

The RZ is going to choke you to death with the dust.

Only the top coat is really hard. The scratch coats are pretty soft. Most guys seen to like the carbide hole saw but I wasn't willing to pay the price. I do think you want to cut up and not down to minimize the damage.

I was doing plaster over wood lathe. I used my AC and air chisel with the V shaped chisel then used a wood bit in the RZ to cut the lathe. I filled around the cans with Durobond but the trim ring would have hidden my sins on all but one of 7.


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## joecaption (Nov 30, 2011)

I was wrong, it's RemGrit.
http://www.homedepot.com/p/RemGrit-...essed-Light-Installation-Kit-GRL502/205623871


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## HouseHelper (Mar 20, 2007)

Easy but messy job using Remgrit hole saw sized for your lights. I have used ones for 4" and 6" cans with success.


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## gottalearn (Oct 30, 2014)

joecaption said:


> I was wrong, it's RemGrit.
> http://www.homedepot.com/p/RemGrit-...essed-Light-Installation-Kit-GRL502/205623871


Thanks -- so basically a carbide hole saw. Did it last many holes? Do you have rock lath and plaster ceilings too?


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## gottalearn (Oct 30, 2014)

joecaption said:


> I was wrong, it's RemGrit.
> http://www.homedepot.com/p/RemGrit-...essed-Light-Installation-Kit-GRL502/205623871





joecaption said:


> Any Lowes or Home Depot sells a grit hole saw just for this. (often in the lighting area)
> Seems like mine are something like Remline brand, there green.
> Replace the 1/4 twist drill pilot drill with a masonry bit.
> There a special size made for recessed lights.
> ...


Yeah, the pan is a great idea. Hopefully it'll minimize the mess (wife will not be happy!)


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## gottalearn (Oct 30, 2014)

HouseHelper said:


> Easy but messy job using Remgrit hole saw sized for your lights. I have used ones for 4" and 6" cans with success.


Thanks -- do you have rock lath behind the plaster as well?


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## HouseHelper (Mar 20, 2007)

gottalearn said:


> Thanks -- do you have rock lath behind the plaster as well?


Yes. Also use an aluminum pie plate between the drill and saw to catch debris.


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## gottalearn (Oct 30, 2014)

HouseHelper said:


> Yes. Also use an aluminum pie plate between the drill and saw to catch debris.


Awesome. Thanks for the advice


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## gottalearn (Oct 30, 2014)

Colbyt said:


> Rock lathe is the drywall like stuff isn't it?
> 
> The RZ is going to choke you to death with the dust.
> 
> ...


Dunno if rock lath is really drywall -- looks a lot like cement to me, but I could be wrong. This is how the walls look like (picture I found on the internet). I would *guess* the ceilings are made out of the same material.

The rock lath is the thinner layer with the brown paper on the outside (the brown paper is inside the wall)


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## gottalearn (Oct 30, 2014)

Colbyt said:


> I used my AC and air chisel


Sorry, what's AC? Air compressor?


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## Colbyt (Jan 27, 2014)

gottalearn said:


> Sorry, what's AC? Air compressor?



Thanks for the pic. That sample looks thicker than any I've ever seen.

*Yes. AC == air compressor.*


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## HouseHelper (Mar 20, 2007)

gottalearn said:


> Dunno if rock lath is really drywall -- looks a lot like cement to me, but I could be wrong. This is how the walls look like (picture I found on the internet). I would *guess* the ceilings are made out of the same material. The rock lath is the thinner layer with the brown paper on the outside (the brown paper is inside the wall)


Looks like the same stuff I encounter... a gypsum material like drywall, usually in 2x4 sheets.


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## joecaption (Nov 30, 2011)

Rock lath is far harder then any sheetrock.
One of my rentals has it and there's no paper on it like that sample.
Yours looks more like plaster over drywall.
Really does not matter because that carbide grit hole saw I suggest will go through both.
May run into an issue with it being so thick, but there's a way around it.
Drill 1/2 through in one direction from the attic and finish from below.


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