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I need to cut a hole in my upstairs hall ceiling for pull down stairs. The ceiling is plaster over expanded metal over wood lath, on 16″ ceiling joists, and it’s in very good condition. Are there any particular methods to use to minimize the likelihood that the plaster cracks extensively from the penetration?
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Keith - This condition is usually a bear to cut and you will likely go through a number of blades (Sawzall?). You can tape the cutline with blue painters tape and that should help protect the edge, but I think the greatest risk to the plaster will be from framing the new rough opening for the stairs.
Jeff
*If you want to keep the plaster around your opening intact I would not recommend a Sawzall (reciprocating saw) at all. Especially if you have wire lath in the mix somewhere. The sazall blade can "snag" on the wire lath and pull or fracture a section free. I've had a lot of success cutting real clean openings in plaster with a diamond circular saw blade. Set yourself up well for dust protection though because it will put out a lot of it. If you can get your hands on a water-cooled blade in a portable curricular like Makita had (or has) then you'll be even better off.
*Ditto on the recip saw. This isn't very different from installing new electrical boxes in lath and plaster walls--except the wire will be harder to cut than the wood. I've been very happy with going through many utility knife blades. I run the blade over the plaster, slowly scoring the surface and then excavating the plaster over the same line, over and over and over. Then I take 24T hacksaw blade and carefully cut out the lath... I would think that eventually you will be able to get at the mesh with cutters after carefully taking off enough plaster.It may be tedious, but reattaching plaster to the wall is no fun either.
*i've had a lot of luck cutting old plaster with a common carbide blade in a circular saw...but ..it's dust city...if you burn the blad.. change it..$7 for a new blade ain't much....plaster... expanded metal lath.. wood lath... yep, carbide circular blade...we have a makita that has a vacumn attachment for cutting fibercement.. that would be the cat's pajammas for this job.....b but hey, whatta i no ?
*I'm with Mike on the carbide blade, even though it's a filthy, dusty job.The problem with plaster on E.M. lath is that vibration will break off the plaster 'keys'. The plaster comes loose and there's no way to fix it.I'd do the rough framing for the opening from the top first and put some fixings up through the plaster and E.M. lath into the framing before cutting the opening so that the perimeter around the cut will be held firm while you saw it out.
*Ditto again the circular saw. An old beater if you have the option. If not, and you only have one saw....shop vac the hell out of it after each cut of the square. And....after years of trial and error....I've found old, dull carbide tip blades to be the best. A old/dull combo blade seems to cut the best. A helper with an extension on the shop vac, held by the saw, helps out. But....be ready for all the dust. Eye protection, dust mask/respirator, drops, plastic sheeting on floors.....maybe temp plastic walls....etc. Or...if it's an unfinished room.....just a damp towel under the door! I like to make two cuts.....first one about a half inch deep to score.....then the second final cut as deep as you need. Layout the cut....then in the middle....cut thru with a keyhole saw....or bust thru with a hammer....and measure how thick the plaster/lath is.....and set the final cut about 1/8" deeper. Jeff
*An alternative to the carbide blade is the abrasive disk designed for skillsaw / masonary applications.They cut with less chipping because the "teeth" are so much smaller. And they're cheap too.Second option: Single tooth scoring tool designed for cutting tile backing board. Works better than utility knife. Slower than skillsaw, but less dusty.
*I'm with you guys who advocate using a circular carbide saw. But you're all right - the dust is a bitch. My current solution involves use of an angle grinder with a 5" thin "Hummer" brand composition cutoff wheel. To achieve the best dust control I duct tape a 4mil heavyweight poly bag over the angel cutter so that the opening of the bag is taped to the shoe of the tool. I then cut a hole at the other end of the bag just big enough for the 2" vac hose and tape that on. Lastly I use a double tank vacuum system that sucks the dust and grit through water in the first tank (something like this but not very well engineered is commercially available for drywall sanding). With this setup I can cut virtually any plaster or drywall surface singlehandedly with virtually no air contamination. The customers love me. And I can breathe easy after the job. One caution: don't try to cut through wood lathe with the angle grinder. Instead, cut to it, remove the plaster, and the keys between the lathe, then use a carbide wood blade to remove the lathe. Good luck!
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I need to cut a hole in my upstairs hall ceiling for pull down stairs. The ceiling is plaster over expanded metal over wood lath, on 16" ceiling joists, and it's in very good condition. Are there any particular methods to use to minimize the likelihood that the plaster cracks extensively from the penetration?