Desperately need to hang my tall leaning mirror because of a crawling toddler at home. The mirror has no hooks and no place to attach hooks. There is a slight gap between the frame and the back of the mirror so cant mount it using wall adhesives. Any suggestions?
Glue a cleat to the back and hang on second cleat fastened to wall. You can cut your own cleat or buy metal hanging cleats.
Or glue vertical 1/2 or 3/4 strips (plywood, 1x lumber) near outer vertical edges (left and right), run a frame wire, and hang it over a hook (or multiple hooks) fastened into the wall.
I'd suggest using standard mirror hanging clips. These happen to be plastic:
Source: Home Depot. No recommendation implied or intended
This happens to come in an 8-pack (other sizes and brands are available). You note that the mirror is "heavy", but don't indicate exactly what that means. I'd suggest that 5 of these clips spaced along the bottom (to support the weight), then one on each side and one at the top (to keep it from tipping away from the wall), would likely do the trick. You would want to ensure that at least a few go into studs in the wall to ensure you're supporting the "heavy" weight adequately, otherwise, these screws will just pull right out of drywall. You should, of course, adjust that as you see fit and to meet your safety requirements. Purchasing more clips would allow you to put more along the top/sides if you felt that was necessary.
If you don't like the look of plastic ones, you could make something similar out of wood. If you have a table saw and router, these would be pretty easy to make. If you don't, maybe a friend or neighbor has one, or you could find a local woodworker/cabinet maker - I'm sure they'd bang out as many as you'd like for a small fee.
There are self-adhesive Velcro-ish tapes and pads designed to carry a reasonable amount of shear force, and you can of course use more of them to make the connection more secure and distribute the force better. They can tolerate a slightly irregular surface. I've used that approach to hang a large (3'x5') 1/4" plywood panel and it has held for a decade. Only downside I can think of is that there will be a small gap between mirror and the surface it is mounted to.