tiling glass tile on glass tile

[L100301]

This might sound like a very stupid question but I am having some problems.
I hired a guy to re-do my bathroom and brought tile that i loved. They were ceramic tiles w/ an accent glass tile boarder approx at chest level. Well the glass tile ars slightly thinner than the ceramic tiles. Well to my surprise the fool did not make the two different tiles flush w/ one another. So now where the thinner tiles are it looks has if the wall has concaved in.
I am trying to repair this. Not using the same guy of course. I was told that I could tile over these tiles w/ another layer of glass tiles to bring up the depth. Is that true. Now the previous tiles were grouted. Is there something special I should do? Everyone keeps talking about ceramic tile. Is it the same? Before I purchase new glass tiles I want to be sure. Is the previous grouting going to be a problem? I have already measured some so the next layer of glass tile should make the two tiles flushed w/ one another. What type of adhesive should I use?
Please help me.

 

[joe-90]

Any ceramic tile adhesive will do, but if it is a wet area make it waterproof adhesive. I would have thought the only problem would be whether there is enough room to add a new tile without it sticking out too far.