Guy,

I've done a few installations away from Troy, I think I did one in Okemos years ago when no one knew what Kerdi was, even out of state. All it takes is a motel and a per diem and there I am.

Thin set mortars are a blend of Portland Cement, silica sand, other minerals, fillers and water retentive chemicals to allow for slow curing and so it doesn't set up too fast. Basic thin set, aka Dry-Set, can be "modified" with polymer/latex additives to improve performance and allow to bond to other substrates. Flexbond is a good modified mortar.

Your suspicions about the trowel is correct. 2x2 mosaics can be a hemorrhoid, that is why labor is more as compare to regular wall tiles. Takes more time to install and grout. You need a 1/8" square or maybe a 3/16" V or square trowel.

You also have to take certain precautions when setting over Hardi. Hardi sucks.....the water out of the mortar. You need to sponge or mist just before you spread or it'll set up too fast, and the tiles might end up in the tub by am.

Jaz

I was going to hive you the exact same advice, but Jaz beat me to it I use a 1/4 inch notch to set mosaics, but mine is worn down and it's really more like 3/16. You can also tilt the trowel more to get a thinner layer. Mix your thinset to a mayonaise consistency.

If your joints are actually 1/8" or less then unsanded will work.
The only reason for sanded would be if the grout joint is larger than 1/8"

Your right on the border line of using either one, so the choice is yours.

If you do use unsanded, just keep an eye out for pinholing. Some unsanded grouts are really prone to it.

I highly recommend using sanded grout even if the joints are a bit smaller than 1/8". It'll give you a nicer, fuller joint. Some sanded grout are recommended with joint of 1/16 - 5/8".

Jaz