Mike, that is an organic adhesive (aka mastic), a Type I Organic Adhesive to be specific, and is recommended by the manufacturer for, and meets industry standard testing for use in wet areas as described in ANSI A136.1. To wit:
Quote:
Originally Posted by ANSI A136.12011-1
3.1 Type I - Organic adhesives for installation of ceramic tile in interior areas.
A. On walls and ceilings having —
1. Commercial construction; dry or limited water exposure requirements.
2. Light construction; dry or limited water exposure requirements.
3. Light construction; wet requirements.
B. On floors and countertops having —
1. Residential construction requirements.
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If you have those conditions, the material is suitable for use. If not, it's not.
You'll find a lotta tile guys, even the more enlightened tile guys here on this site, who will tell you that mastic cannot be use in any wet area. Those tile guys are wrong.
Now, many tile guys will also tell you
they won't use mastic in wet areas, and that's certainly their choice to make.
Some guys simply won't use the stuff at all, and that's our choice.
But the product can legitimately be used per the manufacturer's instructions and tile industry standards.
My opinion; worth price charged.