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I have been trying to find advice on how to do something similar to patch a rock lath plaster wall around my thermostat wires. It doesn't look like the original screws were screwed into anything substantial.The area where I'm trying to patch around the hole in the wall to provide a solid surface to rehang the thermostat screws, but after three coats, the patching is still flimsy and won't hold a screw much less the entire thermostat. The guy at the hardware store suggested a fiberglass patch which I used but now I'm thinking I should have used aluminum? HELP?! See photos to make more sense of the problem.

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From your original picture, here's how I would have repaired it:

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  1. Use some small pieces of (scrap) wood as strapping. Big enough to form a good support but small enough so you can get them into the (massive) hole for the wires. Somewhere between 3/8" and 3/4" would work best.
  2. Anchor the strapping with drywall screws. Ideally they can be placed so they're covered by the thermostat. You can fill these in with compound or spackle if you want to.
  3. Just use regular wood screws (eg, #8 x 1.25" or 1.5") to mount the thermostat to the strapping, no need for drywall anchors.
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    A single piece of wood horizontally will also work (both screws go into it) since the thermostat does not project into the wall.
    – Ecnerwal
    Dec 21, 2016 at 1:21
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Cut a square of drywall or wood roughly the size of the original hole. Place it over the original area and trace with a pencil. Then cut out the traced area and glue it in the hole. Then use the fiberglass patch. You need something to hold the screw and the plaster alone will not do.

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  • Thanks... I knew that in my gut but the guy at the hardware store insisted it would be fine. Ugh. My question to your response is how to I trace drywall or wood when it is on top of the hole, and how do I account for the two small, stripped screw holes since that is where it would likely be screwed in again?
    – cricketsler
    Jul 19, 2016 at 1:53
  • Also, wouldn't I also need to make a hole in the center of the circle I cut since the wires still need to recede into the wall? It sounds like I'd have to actually unhook the wires in order to put a "donut" shaped piece of wood in there...is that what you meant? A donut cut piece?
    – cricketsler
    Jul 19, 2016 at 1:56
  • You'll cut a piece larger than the previous hole(s) making sure that it would also cover the area the smaller screw holes were. So if the previous hole was say 2 inches in diameter, and the screw holes went 1/2 inch on either side for a total of 3 inches, then cut a piece of wood/drywall 3 1/2 or 4 inches square (or round doesn't matter). Then lay that piece of wood over the area the hole was and trace around the plastered area you have now. Remove your wood piece and then cut your plaster area on the line.
    – RadagastTheMachine
    Jul 19, 2016 at 12:52
  • You should now have a 3 1/2 - 4 inch square or round hole that your new piece of wood or plaster can be glued into. Now go ahead and drill a hole in your wood/drywall piece and slip the wires through and then glue the wood/drywall into your hole. After that, apply your fiberglass patch to bond the pieces even more. Once it's set and dried, you can sand or apply texture if needed to match the wall surface, paint and attach your thermostat again.
    – RadagastTheMachine
    Jul 19, 2016 at 12:56
  • Ok, that is a much better explanation. I understand. My question is how do you recommend drilling a hole that size? I have one drill attachment that makes larger holes in metal...can ones designed for metal holes work on plaster? Thanks.
    – cricketsler
    Jul 19, 2016 at 23:54

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