For this project, we used a special type of epoxy that, when mixed with sand, creates a grout that hardens once it dries.
Use a portable cement mixer to mix the grout. Pour in one bag of sand, the color of which will be the final color of the grout. Then add one container each of the two-part epoxy. Finally, fill each of the containers with water and add that to the mixer as well. Pouring the water into the containers allows you to measure correctly and also to use any remaining epoxy.
Let the grout mix for about three minutes, until the consistency resembles pancake batter.