I love making mosaic stepping stones. A couple of years ago, I made a whole bunch of stones. Well, finally I was able to get back to it and make another one. Since the Olympics are imminent, I thought I would make a patriotic, red, white, and blue stone. The flower shaped mold I used came as a kit with the cement, glass, and wooden stick for stirring. I just added the glass that came with the kit to my supply and worked from that. It worked out better for me because the kit came with a little bit of lots of colors and I needed a lot of three colors. As a side note, Lillian's empty baby food jars have come in really handy for sorting all those bits of glass.
First I laid out my design. I knew the actual placement of the pieces would change when I set them in the concrete but this helps me in deciding the design.
Then I mixed the concrete. Be careful not to breathe in the fine dust. When adding water, do so just a little at a time. Of course if it gets too wet you can add more concrete (if you have more). I was using the concrete that came with the kit but for additional stones I had bought some 40 lb bags at the hardware store.
Next step, pour the concrete in your mold and level it off. Now go and clean up your bucket. It only takes a minute and then it's done. Just be sure you mold is in the shade. Before you place any glass in your concrete, jiggle your mold a little to let air bubbles escape.
Now the fun part, placing the glass in the concrete. Just press them in however you like. Don't worry if some watery concrete gets on top of them. You can clean that up later. Once all the pieces are in, just let it sit in the shade for about 24 hours. Then you can go back with a sponge and clean off the pieces that have cement on them. I leave the stone in the mold a couple of days. And once I remove it from the mold, I usually let it sit inside for a couple of more days before putting it outside.
I always bring my stones in for the winter. Otherwise, the freeze and thaws may loosen the glass and it could fall out.