What is it made of, and where do you live? I've had a mirror that I made on plywood about six yrs. ago - hanging on my front porch, so it's sorta protected. It's still in good shape. Also have a cedar post - my backyard pedestal w/the turbine on top that's been outside about the same length of time. On the mirror, I don't remember what adhesive I used. On the pedestal I used thinset. I did have to re-grout the pedestal last fall - was showing cracks. Eventually it'll fall apart, but so far so good. Yours depends on the substrate and where you live. I live in E TX, where the weather isn't extreme - excepting last winter!!!!! Was awful. I did lose a terra cotta planter - was partially mosaiced. Other than that, things go through the winter here pretty safely.

and I live in Michigan. So the elements are somewhat tough (at least compared to Texas) but so is the substrate. I guess I could try it for a while and keep an eye on it and see how it goes.

Help. Can I leave a stained glass mosaic? to hang outside in winter. The stained glass are:
1) glued on double thermal pane window
2) with Marine glue for outside
3) using outside grout (that is used on outside ceramic tiles)

Anne05, I'm going to say "probably." It should be okay.

I would think a major problem in Michigan or other cold places would be water getting in cracks in grout or under tiles, freezing, and breaking up the mosaic. Longer it's out there, the more likely to happen.