What follows is the method I use for hanging my smaller mosaics that I've created on concrete board (Hardibacker). The largest size I've used this on is about 12" x 12". (See comments for some ideas on hanging larger work.)
The hardware must be installed BEFORE beginning your mosaic. I usually obtain the hardware from the specialty drawers at the big-box home improvement stores. I have read lots of mosaic books but only saw this method mentioned online (Sorry, that site no longer exists to link to.).
This is what you need to purchase:
#6-32 size Tee Nuts in 1/4"
#6-32 size 3/8" brass screws
#6 or #8 stainless steel washers
Stainless Steel picture wire
And this is what the Tee Nuts look like. You can get pronged or un-pronged. I get pronged since then they will grip your concrete board and not slip.
Drill with a bit sized for the Tee-nut
Drill a hole in the board and, FROM THE FRONT, hammer in the Tee nut.
Picture on the far left is the front of the mosaic surface and the right picture shows the resulting threaded hole on the back. I use thin-set mortar for glue and that helps even out the raised surface of the Tee-nut.
From the back, add the screw and washer. Repeat for the second hanging spot and you are ready to wrap your picture wire around the screws. The washers help keep the picture wire in place and not slip off the screws.
To see the finished back of a mosaic hung with this method, click on the last picture of my Welcome Sign listing .
See my Etsy MosaicSmith shop for more mosaics art:
I also create original design silver jewelry: https://www.etsy.com/shop/MosaicSmith?search_query=jewelry