In article .com,
thetiler wrote:

Forget what anyone says, never use mastic to set floor tiles.
It takes a long long time for it to fully harden, and in that time
you'll step on the tiles and move them slightly, breaking the
bond. With the great thinsets available, there's no reason
to ever use mastic to set floor tile.
The temptation is that mastic comes pre-mixed and therefore
is easier to use. Actually it only takes a couple of minutes
to dump out some thinset in a bucket, add water and achieve
a similar setting adhesive that will harden in hours, and not
weeks or months.

thetiler

I followed your advice about my living room ceramic floor tile job a
couple weeks ago. Just wanted to let you know everything you told me
was accurate and made the job much less stressful. The floor looks
beautiful.

I just wanted to thank you for your assistance.

-Frank

--
Here's some of my work:
http://www.franksknives.com/