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tldr; Why do magnets stick to my ceiling?

I have an old house, built in 1905 in the Boston area. I want to install a light fixture in a room that does not currently have one. I tried using my stud finder to find the joists, but it proved futile.

I switched to trying to use some neodymium magnets to try to find nails in the ceiling. Right off the bat, the magnet stuck. Thinking I was lucky, I grabbed a second magnet and started hunting for another nail. That magnet also immediately stuck.

I started hunting around and found that the magnets stuck to my ceiling virtually everywhere that I put them.

The ceiling has a textured plaster finish on it. There are no vents running through the ceiling that I am aware of.

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    If the ceiling is plaster-over-lath, there is sometmes a metal grid embedded in the plaster to help hold it on the surface. I suspect this is what you're findimg. How old is tbat ceiling? – keshlam Nov 30 '15 at 19:28
  • Is there a room above with floorboards? The floor brads will show where the joists are. I presume you want to place the light fitting 1/2 between the joists? – DavidPostill Nov 30 '15 at 20:14
  • @DavidPostill There is a room above, though it belongs to my neighbor. I might be able to coordinate with them, but it could be difficult. – dave mankoff Nov 30 '15 at 20:58
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I would assume it's because you have plaster ceilings that use metal lath.

enter image description here

  • Can you source where you got the image from? Thanks – Kevin Brown Dec 1 '15 at 7:03
  • @KevinBrown sorry, don't have anything beyond 'the google'. Feel free to swap it with another if you'd like. – DA01 Dec 1 '15 at 16:32
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The plaster is probably applied over diamond mesh metal lath as shown in the photo below.

You probably need to drill exploratory holes to find a stud. Can you drill from above?

Image removed due to copyright

  • Can't drill from above, sadly - the floor above is another condo. – dave mankoff Nov 30 '15 at 20:57
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    I don't believe you're allowed to post that image here, Inspectapedia images are copyrighted: MAKING ELECTRONIC COPIES OF our WEBSITE CONTENTS (such as copying our pages, content from our pages, or our graphics to another website or into email) IS EXPRESSLY PROHIBITED - this website is © protected material, all rights reserved. – Johnny Dec 1 '15 at 5:29
  • @Johnny everything is copyrighted. Copyright has allowances for fair use. This typically falls into fair use. – DA01 Dec 1 '15 at 17:58
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    "You agree that all Subscriber Content that You contribute to the Network is perpetually and irrevocably licensed to SE under the Creative Commons Attribution Share Alike license", I fail to see how that is fair use. Also, see this meta post on fair use at SE. At a minimum, a link back attribution should be included to give some traffic (and search engine reputation) back to the source. SE may be educational, but it's not non-profit, which dilutes the case for fair use. – Johnny Dec 1 '15 at 18:08
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Although the house was built at the turn of the century When wood lathe was usually used for plaster walls, it might be possible that extruded metal lathe was used sometime recently. Does the same occurrence with the magnets happen any place else? To verify it's not the nails securing the lathe to the studs, positively locate a stud or joist and measure 14 1/2 inches over to the edge of the next one. See if the magnet sticks anywhere between the two marks. If not it had been magnetized to the lathe nails.

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    I think metal lathe in ceilings goes back about 100 years as well (if not longer). I tore out metal lathe+plaster ceilings in a 1927 home (which I'll never do again...THAT was work...) – DA01 Nov 30 '15 at 21:40

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