Is Button Board ("Rock Lath" or "Plaster Board") harder than Cement Board?

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Mar 21, 2019
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Los Angeles County
I need to cut 16-20 holes (appx 6") for recessed lights in my mid-50s button board ceilings ("rock lath" with a layer of plaster over it). I understand a typical drywall hole saw will not be up to the task. Some recommend diamond-coated hole saws but I just came across this adjustable hole saw that says it will work on cement board. Is button board harder than cement board, and if so, is it sufficiently harder that this saw would likely not stand up to 16-20 holes? Thanks.
Button board is of a different composition than cement board and is closer, in composition, to fire rated drywall besides which, the saw kit is relatively inexpensive.

I presume you are installing recessed can fixtures, so, if there is insulation, be sure you are installing IC rated cans.

If you are permitted, the
inspector will ask, and besides which, the rating tags are visible inside the cans.
Be sure there isn’t expanded metal lath over your rock lath.

The type of hole saw you have linked relies on the center drill to keep the cutting action lined up. In softer material the center hole can get wobbly and open up and with just two teeth cutting will want to grab. The other problem happens when it breaks thru on one side slightly before the other. I’m not sure the dust shield acts as a guide to keep it all square.

With a regular hole saw there are teeth all the way around.

I have done them with a saber saw or scroll saw and also the rotozip tool following a template. Get a helper to hold the shop vac.
Thanks for the input.

I'm putting in IC-rated "puck" LED lights. There's no metal lath. I have a Klein hole saw similar to the one linked but it is meant for drywall so I don't think it will hold up on button board. Guess I could try it and it it dies, it dies. Maybe it would just be better to spend the bigger bucks on a regular diamond hole saw.

Related question, 12 of these new LED lights will get their power from a 15a circuit that currently only has one bathroom fan and 2 attic light fixtures (both LED bulbs). The house and original wiring are not grounded but I have a new electrical panel that is grounded and I may eventually rewire the house with grounded cable. I figured I would wire these new lights with 14/3 and attach the grounds to the lights, but just leave the ground wire unconnected when I tie in to the (ungrounded) power source (J-box in the attic) rather than attach the ground wire in the ungrounded J-box. Then when/if I run new grounded 14/3 to that J-box I can connect the ground then. Is that the right approach?
Be careful when using romex in the attic, if or when you crossover ceiling joists, you have 2 options, either drill holes in the center 1/3rd of the joist width, or use a cat-walk, which in general terms, is a 1x6 nailed across the joists, with the romex over the top of the joists, stapled beside the cat-walk.

Often times before romex with ground
conductor included, electricians in your area, would add a ground pressure clamped to boxes which because of the size of the conductor and the use of plaster, went unnoticed.
I have a set of DIABLOS and a 3 cornered file.
Hi MattinCA,

I've cut and drilled holes every day of my work life. Below are some observations:

Diamond hole saws aren't a good choice for plaster, drywall & similar materials that powder finely. Nor are they suitable for soft materials such as gypsum based anything. The dust clogs the spaces between the diamond grit dust, stopping them from cutting. They're more suitable for concrete, granite & similar hard materials.

Klein gave me Klein 53710 adjustable to evaluate. It's OK, but S L O W (as are all of that type).
It can also rip the drywall paper if you're not careful. at the start & end of cuts.

But, I cut an awful lot of holes with it and it's still cutting well. It never lost it's adjustment- not even once. (Others I've tried do. It can wreck a hole quickly!)

I prefer traditional hole saws with arbors. Push-pull arbors, such as Starrett's are convenient. You can get bi-metal (usually M2), carbide, diamond. The bi-metal are easy to sharpen when needed. I recently used a 5-1/2" Starrett Fast Cut for many holes in plaster-on-metal, wood & blueboard laths. It held up well.

If this is a one-time-use tool, maybe try a cheapie one from Temu or Harbor Freight. When you're done, drop it in the recycling bin.

*HINT: Be Sure you know what is above where you're drilling. Wires? Pipes? Ducts? Structural? The cat?

Enjoy Your Project!

You Didn't Ask, but here's an unsolicited editorial about your wiring plan:

Since the equipment grounding conductor in the new NM cable is not grounded at the source, you're supposed to snip it off flush with the jacket in each box so no one thinks it is usable & attaches it.
To leave it disconnected from earth creates what's called a "Floating Ground". This can be quite dangerous.

(Caveat: Although a master electrician, my career was primarily industrial & high voltage distribution, so the preceding sentence is based on jobs helping friends in houses & rehabbing buildings that I owned.)

Also consider that many LED dimmers won't work properly without a grounding wire. The lamp(s) will clip at about 10% brightness.

This snipping certainly messes up the project when you do have a chance to ground the circuit, so If at all possible it would be a good time to fish this cable back the the load center & ground it.

But All may Not Be Lost...
Test the boxes in your home for grounding. They might be grounded and you don't know it. If your house has BX cable (common in the 20's - 60's), the trace wire might be bonding the box at the clamp where you can't see it.

To Make Re-Wiring Less Intimidating-
As far as re-wiring the house so everything has an equipment grounding conductor, think of the job in a piece-by-piece fashion. How often do you need a 3-prong, grounded receptacle outlet in the living room? The bed room? They can wait- or be skipped.

Also while working on the re-wire, you might as well update to new code rules.