Do I also need to apply thinset to my Subway tiles or is it enough to just put it on the wall?
Back-Buttering shouldn't be needed. But, the best determination is to set a tile &amp; then pry it off. You should have a nice even smush of Thin-set that covers the whole back of the tile. If you don't get full coverage, then you can try it again with a bigger notch trowel...on a fresh clean tile. If that doesn't do it, then you'll want to back-butter every tile.