I found this forum by searching for advice on pre-mix mortar, and it lead me to this thread:
Basically, my situation is this. I've installed 5 tile floors before, and each time I have used powder mix. My mother-in-law asked me to replace her hardwood floor for her, which is in the same room as the fireplace. The tiles surrounding the fireplace did not extend far enough to stop embers from making burn marks in the old floor, so she asked me to add one more row of 12x12 tiles as I installed the new wood floor. She went and bought all the supplies, asking the guy at the local store what she needed.
Mind you, this is all in France (my wife is French) and I do not speak French and there are a lot of products I've never seen before, some of which seem to work well. So it's easier if someone else does the shopping. So when I saw mortar in a bucket, I figured why not? However, to match the height of the existing tiles, I needed to put on a little over 1/4" of this stuff. After 36 hours, a couple of the tiles still move a bit.
In the post quoted above, the poster said it can't be used "too thick". My questions are: what is 'too thick', and at this point should I try to pull it up and re-do it, or should I wait it out? This is an area that can go for months without being walked on if need be.