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Thread: Please help find studs in plaster walls

  1. #1
    Join Date
    Dec 2004
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    Delaware Valley, PA
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    Please help find studs in plaster walls

    Hi, guys. A couple years ago I put up crown molding and picture rail molding in my home, which has plaster walls on 3/8" lath. (It's the original 90 year old plaster.)

    Finding the studs was a chore, because the studs are often not at even intervals, and sometimes the lath has separated from the studs, so tapping with a mallet or probing with a nail doesn't work well. That electronic stud-finder gadget (I forget its name) was even less reliable.

    Now I want to put up chair-rail and picture rail in another room, and I'm looking for a better way. I'm toying with the idea of using some sort of tool to cut through the plaster just deep enough to graze the studs. The groove would be hidden behind the molding, so I'm assuming I would not have to fill or patch it.

    What problems would I have with that plan? What would be your tool of choice if you were to try it? Other suggestions on how to skin this cat?

    Many thanks in advance.

    Regards,

    John
    What this world needs is a good retreat.
    --Captain Beefheart

  2. #2
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    I'm not familiar with working with plaster walls at all, so take these comments with a grain, or 2,000, of salt. I think your idea of skimming to find the studs would work well. Mark your line, but I would use a jab saw so that it stops at the stud, you could mark it, go to the other side, and cut to the next one, and so on. Do you have a way to make sure there are no electrical lines running up and down in a wall cavity? Is the top of the wall in an attic where you could see if a wire is running down through the top plate? I wouldn't want to cut into one!! Do you need to fill back in the cuts? I don't know, but I'd think it would be a good idea to do so before installing the trim. If nothing else, it could help keep the two sections of wall from moving separately and creating other problems. So my guess would be plaster material, or something made for repairing cracks in plaster walls.
    You might also make a "story board", maybe out of cloth or string that wouldn't shrink, and mark the stud locations on it for future use on the same wall.
    Another place to search for answers would be the "This Old House" web site. They should have something on plaster repair if nothing on your specific questions. Jim.
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  3. #3
    Join Date
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    Why cut the slot? Use a drill as a probe. Make a line where the chair rail will eventually go. Drill holes through the plaster along it. When you poke through the plaster+lath into air, that feels very different from poking through into a stud. Mark where you find studs. Use found studs to give you an estimate about where to find the next one.

  4. #4
    Join Date
    Apr 2008
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    south of Atlanta
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    A metal detector should work. It should find the nails that a holding the lath on.

  5. #5
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    Those super magnets will find drywall screws. The big ones will stick to the wall.

  6. #6
    One problem you may run into, is that the lath may not run in exactly parallel lines, so that in the width of the chair rail from one wall to the next, you may find a gap to probe at one end, and not in the middle or at the other end.
    Also, while it is possible that the stud spacing is uneven (I find this even in new homes where other tradesmen move studs slightly for their convenience) it could be the framers used a different spacing, which was fairly common back then.
    Most tape measures will have a mark at 19 3/16", 38 3/8", etc.
    The mark will be a small black diamond at the top of the tape blade at these measurements.

    One other suggestion: instead of using the hammer to tap the wall, try using the heel of your hand. It makes a duller "thump" which is easier, at least for me, to hear the different sound where a stud might be.

  7. #7
    I used the riubber coated end of my plumb hammer and then when I think I'm on I whack it with my knuckles closed fist and listen and feel.
    Usually that get's me spot on but when I don't gee all too sure I take a power drill and a small bit and pierce a string of holes laterally out from the place where I think center is. Starting of course in the center.

    As often as not that lets me locate a stud's sides telling me where the center of the stud is.
    The holes can be filled with joint compound.

  8. #8
    Join Date
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    I've got plaster walls too, and finding studs is a pain.

    The idea of cutting a slot seems like a bad one to me. Assuming you complete that without breaking chucks out (which is easy to do), you are left with the plaster having a loose edge which is just inviting chunks to fall off later (if you are going to do that, at least patch over the groove later with patching plaster). The vibration from a power saw can be pretty good at loosening the plaster from the lath on some plaster walls.

    Use any and all methods available. For me, thumping with my hand is usually the most accurate. Most stud finders are terrible, but they may help reinforce other results. Take a concensus of whatever techniques you have to locate the highest-probability areas and then confirm using a drill. Once you get past the lath, there's no mistaking drilling into air versus into a stud. A series of tiny holes localized to where the stud seems to be is a lot less impact to the plaster and less to repair. Even thought the spacing isn't even, measuring usually gets you close enough to locate the next stud approximately with a little thumping.

    I am curious to see how well a fish finder would work ...

  9. #9
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    I use a lumber wizard metal detector. It finds the nails used to hold on the lathe. Regardless of stud spacing, every piece of lathe was nailed at every stud. I think Zircon came out with a stud finer that is supposed to work on plaster walls due to its ability to sense metal, maybe this one: http://www.zircon.com/products/center_ms_i320.html

    I haven't used that one so I can't say how it works.

  10. #10
    Join Date
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    Western Nebraska
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    I've seen one of the more expensive stud finders work well. Can't for the life of me remember the make of the danged thing... Most stud finders are crap.

    Zircon! Thanks Peter.
    Last edited by Steve Rozmiarek; 08-08-2009 at 10:48 PM. Reason: Added name

  11. #11
    Join Date
    Jan 2009
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    That's a good idea. I'll have to see if my wizard detector works.

    I have a Zircon detector (not the same one) that doesn't work at all. The cheap Sears detector I have from decades ago works much better, but is still not great on plaster.

    (Of course, I have metal mesh lath not wood lath, which means i'm pretty much screwed on the metal detector thing. Density measurement is the only chance.)

  12. #12
    If you have a foot panel on that wall then you can take a look at where the nails are located. Most likely they are where the studs are. You can also remove the foot panel and then poke there to find the studs.

    Michael

  13. #13
    When I was remodeling hotels we would use liquid nail and shoot nails in opposing angles(toe nail). With hotels having metal studs saved time and money without having to cut open walls and install backing.

  14. #14
    +1 on using a drill. I do it all the time. I find stud centers to be from 14-18 OC all the time. Start at one side of an electrical outlet to find your first stud. Once you hit a stud drill to the left and then to the right to find the edges. Mark with pencil or painters tape above where the chair rail goes, move 16" and start drillin' again. Once finished, patch the holes..Easy!

    PS. The plaster will trash the drill bit (1/8") in no time so plan on sharpening or replacing it.
    Last edited by joe milana; 08-09-2009 at 1:36 AM.

  15. #15
    construction adhesive and few brads.
    take the easy way out.

    using nails/hammer would damage or destroy the plaster keys.
    VHB double sided tape is even better.


    good luck.

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