I've never done or heard of this, but most of my small tile work has been with presheeted tiles
I did read about a mosaic system where the layout was done face up and a mesh was attached, and the tile was thin-setted and afterwards grouted.
I've also seen a TOH segment where the mosaic was attached to a thin cement board (1/4"), grouted and then the whole assembly thinsetted in place.
For me, grouting from the back would mean that you couldn't know or change the amount of grout that was pushing around the mosaic. Normally, cleaning the tile of extra grout would be done in 20 to 30 minutes, before it is set solidly.
This method would let the front face be flat and the variations hidden in the back.
What would you glue the tiles with? I assume some type of water soluble glue...
Found a tutorial here this is similar to your method, called the indirect method. Do the reverse attachment to paper, install the tile on the wall (floor?), let dry and THEN grout. This makes more sense to me and overcomes what I see as a potential problem area, not being able to control the grout removal.
Absolutely. Those tiny tiles will chip or pop off as soon as somebody smacks it with something. I assume you are thinking of some nosing like this and where I live, I would certainly go with something with some grip.
Not knowing what kind of traffic the stairs get and what your climate is like (how often it freezes - how often they are wet), it's hard to make a more informed recommendation, but those thin small tiles will not take much abuse.
Best Answer
Your thinset should be like peanut butter. If it is too thin then you could have possible issues with mosaics and flooring. Basically you could push down to bare floor or close to it.
A 4mm trowel is perfect size for most mosaics. I think that your issue is that either you aren't combing the area well enough after dropping down your thinset or possibly you are pushing down to hard.
The installation method for any tile but especially a mosaic is to comb the area in a direction, sit the tile on the area, then gently press the tile into the thinset perpendicular to the thinset streaks back and forth. If you were to just press straight down hard you would have a lot of thinset in between your tiles and as mentioned before not enough behind the tiles.
Also you will always have a little spillover. You don't have to clean out all of the thinset in between the tiles. Your grout will bind to the thinset fine so you just need enough room for the thinset to not show.