I am pouring mosaic concrete stepping stones to be placed in a city sidewalk. The mosaic will go face down into a form and the concrete poured from the back. I have been having problems with my test tiles in getting the sand to move all the way forward to the level of the face of the tile and have been ending up with air bubbles in the surface where I want it to be flat.
How can I alleviate this problem? Would pouring a mixture of just sand and cement first to fill cracks and then pouring the rest of the mix with the gravel behind it solve the problem or would it weaken the top surface of tile?
Normally I lay the mosaic on top of something with mortar, thin set or other adhesive and grout once the adhesive is dry. Not sure how to duplicate that with a concrete pour.