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I want to modify a wall so that small magnets will stick, and even hold a small dead weight. I would prefer that the magnetic area not look all that different from the rest of the wall, I don't want to just hang a sheet of steel. I am imagining that 1/4" mesh hardware cloth could be attached to the face of the drywall, and skimmed over with joint compound. We will be skim-coating the walls in any case to get a specific plaster texture.

The hardware cloth I've looked at has 1/4" openings, and is woven from 23 gauge steel and zinc galvanized. Magnets stick nicely to the bare cloth. My concern is that the joint compound will react badly with the galvanization causing the wall surface to check or fail in time.

The wall in question is in a full bath, and so humidity is likely to be higher than in the house in general. One of the proposed locations is directly behind the sink, the other is open wall. We are still discussing the right spot.

Is this a viable approach? If not, what else should I consider?

Update: My intent is to use rare-earth magnets to hold up a glass mirror behind a bathroom sink. The mirror is a 20 inch square cut into seven pieces forming a puzzle. Using magnets to mount the mirror will allow guests to play with the shape of the overall mirror on the wall. My plan is to epoxy three NdFeB magnets to the back of each puzzle piece, or possibly just one on the smallest pieces.

The back of an envelope says that 400 square inches of 0.25 inch glass should weigh a couple of pounds, but I probably should go weigh the actual pieces since Amazon thinks the shipping weight is 4.6 pounds and there can't be all that much cardboard in the box.

Assuming the 4.6 pound figure is correct and that the box accounts for about .6 pound, the smallest pieces would 1/16 the total weight, or about 4 ounces, and the largest pieces would be 1/4 the weight or about a pound.

So the bottom line is that I do need a surface that will allow magnets to hold up about a pound.

Final Update: As all things in a home remodel are in continuous flux, this plan has fallen by the wayside. The answers and discussion have been helpful. I believe the mirror will find a home on a steel-backed whiteboard in the home office, and something more conventional will end up on the walls next to the sink.

I still plan to play with the magnetic primer paint, but from all I've read I'm not expecting it to work out to hold up anything more than a few sheets of paper. With that in mind, the answer pointing to the useful permanent magnet calculator gets the coveted green checkmark mostly because it has been the most useful in guiding us towards a location and use for the mirror.

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stainless steel sheet with some wallpaper/paint would do fine –  ratchet freak Sep 17 '13 at 23:26
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@ratchetfreak some types of stainless are not magnetic. –  mac Sep 18 '13 at 14:42
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FWIW, I would not hang glass objects using any technique that I wasn't completely confident in. –  Reid Sep 18 '13 at 20:01
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Don't do stainless steel. It may not be magnetic. Just prime and paint, or otherwise coat, a sheet of regular steel. –  Edwin Sep 18 '13 at 20:16
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If this was in a public bathroom, and your insurance company knew about your plan, they'd likely want you to use plexiglass mirror panels rather than glass. Magnets or no magnets, this puzzle is somewhat of a safety hazard. It might not be horribly dangerous, but the element is there. I mean, people (possibly children?) are freely handling one pound glass panels. People have wet, soapy hands in bathrooms, too. –  Kaz Sep 19 '13 at 1:42
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3 Answers

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If you really want to securely hold objects that heavy to the wall using magnets, I think you need to be working with sheet metal on top of the drywall (or in place of the drywall).

The magnetic force will fall off very quickly with distance away from the plate, so even skim-coating with plaster will dramatically reduce the holding power of the magnet.

enter image description here

If you want the surface to blend in with the surrounding walls (you didn't actually state the finish on the walls, but I'm assuming it's painted sheetrock or plaster), try simply painting the steel sheet to match. The texture of the finish might be slightly different, but I'd imagine it wouldn't take away from the feeling that it "blends in" with the surrounding walls.

As others have stated, I'd also consider a polycarbonate mirror rather than glass.

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The wall finish is a plaster skim coat over drywall, in the "catfaced" style. The top coat is a skim coat applied with deliberate voids that are perhaps 1/32" deep and typically about a square inch of total area. I can paint a steel plate the same (or a deliberately contrasting) color, but I don't think I can readily match the texture. I'm not interested in machining a steel plate to have faux-plaster finish. –  RBerteig Sep 19 '13 at 20:34
    
Thanks for the link to that calculator, I have other uses for that sort of information. –  RBerteig Sep 19 '13 at 20:35
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They make a magnetic primer that just paints on the wall under your paint. I have not personally used it but in theory its by far the easiest option.

enter image description here

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I've used this. It does not work very well. If you have super strong magnets and lightweight objects, it is OK, but it's not anything remotely resembling the hold of a refrigerator (e.g.). The texture does vary a bit from regular paint (it's basically just metal powder mixed into the paint). –  Reid Sep 18 '13 at 4:23
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If people are going to be sliding magnets over this all the time, I'd be worried about the paint coming off, even if the paint wasn't attracted to the magnets! –  BlueRaja - Danny Pflughoeft Sep 18 '13 at 18:43
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One pound flat object glued to three magnets? I don't think that's going to stick to a thin coat of some paint with suspended ferromagnetic particles (or whatever this is). Maybe if you put on fifty coats or something! –  Kaz Sep 19 '13 at 1:32
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I've used it. IMHO, it's crap. After 5 coats I still couldn't get a magnet of any heft to stick. I finally just got some sheet metal and painted that. –  DA01 Sep 19 '13 at 16:41
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I've got a can on order to try some experiments. Reviews I've found online seem to be highly polarized, either "wow" or "ouch" and hardly any "meh". The bad reviews include a large percentage of obvious failures to follow directions, hence the urge to try it myself before buttoning the wall up. –  RBerteig Sep 19 '13 at 20:41
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Another option would be to cut a chunk out of the wall and hang a steel plate behind the drywall, then repair the drywall.

Repairing the drywall is not as daunting a task as it sounds like. See here for more information.

If the magnets you use are anywhere near as powerful as the ones in this stud finder, then three of them will easily be able to hold a few pounds.

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Small magnets won't be strongly attracted to steel plate that is 3/8" away (or whatever is the typical drywall thickness). –  Kaz Sep 19 '13 at 1:35
    
We have the room stripped down to studs at the moment, so floating plaster on expanded lath or putting something on either face of the drywall before final finish is certainly an option. This week. Soon, the options will be narrower. –  RBerteig Sep 19 '13 at 1:47
    
@Kaz: The drywall in my home has two layers; I've measured it to be 1" thick. That magnetic stud finder is attracted to the outlet-box nails behind the drywall strongly enough that it easily holds itself up on its own. –  BlueRaja - Danny Pflughoeft Sep 19 '13 at 2:50
    
@mike: My logic does hold, because OP and I are talking about exactly the same thing. That magnetic studfinder is not an electronic studfinder which uses magnets; it is literally just a really powerful magnet. When I hold it up to the wall, it's attracted to the nails behind the wall so powerfully that it can hold itself in place. –  BlueRaja - Danny Pflughoeft Sep 28 '13 at 21:20
    
@Mike: ...I'm aware of all those facts, but they don't change the fact that my answer is still correct. –  BlueRaja - Danny Pflughoeft Sep 29 '13 at 3:39
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