QUESTION

Adhesive and Grout for Underwater - Is there a waterproof grout and adhesive? One that could be underwater such as in a birdbath?

ANSWER

ANSWER - First of all they only way to truly waterproof a tile installation is to use waterproof membrane.

I think your question is whether or not there are grouts and adhesives suitable for being submerged in water as in the case of a bird bath.

Many cementitious dry set thin-set mortars and grouts are suitable for use under water.  You do need to let them cure for at least 14 days before you submerge them.  There are epoxy adhesives and grouts that might not require as long of curing.  When you buy the thin-set dry set mortar make sure it is recommended for that use.  The latex or polymer modified versions will normally provide better performance.  Make sure the substrate to which you are bonding the tile to is properly prepared.  Good luck.