cutting into lath and plaster
I’m getting ready to cut into a ceiling to install a whole house fan. The ceiling is drywall screwed to lath and plaster. Previous attempts to cut through laths have resulted in large chunks popping out. Another carpenter suggested reversing the blade on my saw so that the plaster and wood laths are scraped instead of chipped away.
Has anyone tried this method? Any experiences or suggestions?
What type of saw is it? If you're talking about a sawzall, I think it will work if you reverse the blade and lay the saw flat on the surface to plunge cut at a low angle. I did some wall penetrations like this, but ended up going in at 90 degrees at the end to get the lath.
Can you cut from above? The key is to get all the way through the lath before the whole assembly begins to fall apart. A circular saw at shallow depth might get it.
If you're going to frame it, maybe build the frame first and screw the lath to it. It's always easy to cut near framing.
"If you're talking about a sawzall, I think it will work if you reverse the blade....."How do you reverse a sawzall blade? Sorry, I'm just having a hard time picturing this.
On the foot of your saws all there is a toe and a heel. Turn the blade so the teeth face heel.
That way you can lay the saw closer to the drywall and cut more sideways to the drywall instead of the blade being perpendicular to the work.
You turn it around in the chuck to that the teeth face the top of the saw. Then you can lay it flush on a surface and plunge cut. Somebody posted a video about it here a month or two ago, which is where I learned it :).
Thanks, what an idiot I am.Sorry, I was thinking end-to-end reverse (!!!) Duh, silly me! :o}Yeah, I actually install my blades the way you describe more often than not.
Edited 2/1/2009 12:28 am by kenhill3
Well, honestly I never thought of it until I saw it in the video. It made for some squirrely plunge cuts the other way around -- wedge shaped kerf while the blade bent all over, etc. I'm not sure how well it works with lath. It goes through drywall and plaster just fine, but lath bends all over, and hinges inwards when there's a joint nearby. A fine-tooth blade is probably best.
Any time old plaster is involved its a messy job. Lots of dust sheets and a very good vacuum on hand.
Good news is the plaster is sandwiched between the drywall and lath.
Last time I used an angle grinder with a masonry blade with the vac catching the dust. Well most of it. I cleaned off the lath on the inside of the cutout.
I used a rotozip with wood cutting bit for the lath. I used the vac all the time to control dust.
plunge cut, circular saw.
if U want to limit the dust, since the finish is drywall, utility knife the drywall out of the way then plunge cut. You can also use the utility knife to score and snap the plaster first.
Have a helper? Just plan on plunging while they hold the shop vac beside the blade.
Artistry In Carpentry
I had to cut in 8 10" ducts in my house in the ceiling and found that a piecce of 1/2" plywood that was long enough to catch 2 rafters or strappings and screwed it in with some drywall screws to the rafters/strapping. I had previously cut a hole in the plywood bigger than the one i needed and drilled a couple of 3/4 holes and used a jig saw with a sharp down stroke blade and it worked awesome. Having someone holding the shop vac hose made it easier
This method will work a lot easier in your case because you have access from above. I came up with this method when I had to cut out lath the length of a room for a new drain for a new bath.
Drill holes in the four corners so you can see from above where you are. Next vacuum the cut line clean. Use that expanded foam stuff to glue down a strip of wood to the lath and plaster just out side of the line you want to cut. I used strapping but I guess you could use 2x4s if you wanted. Let the foam fully harden. At least a day. Cut out as usual with your Sawzall. Because the lath is held tight it won't vibrate in and out knocking off the plaster and making it easier to cut the lath. I your case where there is Sheet Rock under the plaster, I'd add a few screws to hold the Sheet Rock in place too.
Nice idea - alternatively, working from above, with the corners drilled through for reference you could use a circular saw or grinder to cut down through the plaster and lath, but not quite deep enough to cut through the drywall on the bottom. All the plaster dust would stay up in the attic.Then you could use a manual drywall poke saw to finish from the bottom up - this would keep the dust in the living space to a minimum.
this sounds like a great method - I'm up for trying it....
I would use a 4.5" grinder with a diamond wheel.
Perfect job for Multimaster, or the cheap Rockwell and Dremel knockoffs. I may be slow but no chunks vibrating loose.
"Shawdow boxing the appoclipse and wandering the land"
Edited 2/1/2009 11:10 am ET by dedhed6b
thanks everyone -
The plan was to drill the 4 corners from above, chalk the cutout on the underside (drywall), score through the drywall to avoid tearing the paper, circular saw plunge cut from below, then finish the corners with a handsaw.
Having cut through drywall before, I totally agree that having the vaccum is an imperative.
I hadn't considered the sawzall method. I had previously tried using a sabre saw to cut out an electrical box opening and that's when the laths let go and I chunked a section of wall.
wish me luck.....