I would like to install fans and and ceiling lights at different locations on a concrete ceiling and not have the wire or the conduit visible. I've seen previous posts recommending a trench as a solution and like this idea. Is there a minimum depth to the trench? (I also tried to find out if the OP of a similar question had successfully pursued any of the solutions offered but that query was deleted for some reason).
Concrete – what’s the minimum depth of a wire channel in a concrete ceiling
ceilingconcrete
Related Solutions
Looking at the geometry, it can only be paint holding it up. I would stay away from any solvents.
I would add a second putty knife, with a stiff blade. Use a slightly larger (wider to distribute the force of the lifting blade) putty knife against the ceiling (and under the lip of the fixture). Put the stiffer, skinny blade between the wide blade and the fixture. Pry up slightly, all around the circumference of the fixture. You will break it loose.
The prybar is overkill (in the photo), but illustrates how to protect the underlying drywall. (Guess what happens if you use the prybar alone. Ask me why I know :-O)
Good plan by Christos regarding leaving the new fixture, though I believe you will succeed removing the original.
Well...I had to live and learn. I used 12 inch sonotubes with the same anchor and cheap cement (the fence post kind that was recommended to me) and 6 x6 posts, which turned out to be a bad idea. 2 of the 4 cement piers cracked part way down where the achor ties were. My solution was to build 21 inch squares around the base about 12 inches down and past the broken areas and leave the rest of the existing footing intact with the more expensive extra strong cement surrounding the existing pier that goes 3 ft down. Hopefully this holds up well..but I am a DIY person so there is trial and error on my end. Get quaility cement and do a wide base to limit lateral breakage IMO. Of course I dont think there would have been and issue if I had not used cheap post hole cement. I am just glad I discovered the issue before the structure became wobbly.
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Best Answer
If you cut a "trench" in a concrete ceiling, you potentially weaken the strength of the structure. Not a good idea. Better to use already available surface mount wiring channel (trade name "Wiremold" for reference only) and if it bothers you, change your attitude about it. Or hide it beneath some architecturally unnecessary structure, like a faux beam made of stryrofoam and painted to look like the concrete (people sell this for that exact reason). Compromising safety for aesthetics is never a great plan.