Hans: I have seen stained glass inserted into garden paving stones (the cast concrete type) so I think your project will work fine. Here are a couple of ideas: 1- Keep the glass pieces small (1-4 square inches) so that if the glass cracks it will be less noticeable. Smaller pieces on the floor will be less slippery as well. 2- Thinset bonds well to the glass, but don’t use it to make up for the difference in thickness between glass and tile. When thinset is applied too thick it shrinks and cracks, and you don’t want that to happen to your glass! 3- Pre-assemble your border on strips of thin stable substrate like Hardie Backer Board. Make sure that the overall thickness matches your tile. Then you can just thinset your borders into place at the same time you install your tile. Carefull not to bend the strips as you install, otherwise your glass may break. 4- I have also used crack suppression membranes (like Protecto Wrap) to pre-assemble my borders. I thinset each piece of glass on the surface of the membrane that has been cut into the right size strips. When I’m ready for the installation, just peel off the paper backing and apply the strip directly to the substrate. Again I use a proper backing material screwed directly to the floor to make up the difference between tile thickness and the glass. 5- Once I installed the glass directly to the sticky side of the crack suppression membrane. That made the assembly of the border really easy and the glass sticks like crazy to the membrane. Then I used thinset to apply the fabric side of the membrane to the substrate. It worked really well, but some of the colors of glass can be affected by the black membrane backing. 5- Make sure the grout is all the way flush with the surface of the glass to prevent anyone from getting hurt on those sharp edges! I hope that some of these ideas work for you.