On May 10, 6:44�pm, "Jay-T" wrote:
I am having new ceramic tile installed on my shower/tub surround. �The job
is being done well -- with cement backer board etc.

My question is about the 1/8-inch gap between the bottom of the ceramic tile
and the existing cast iron tub. �Should that space be filled with grout and
then use 100% silicone caulk, or should there be no grout there and only use
100% silicone caulk?

As there could be movement between the tub & the wall you need
silicone caulk or better still there exists soft plastic "angle piece"
with a fin that goes under the bottom tile and rests on the tub. A
permanent stain resistant solution that never leaks, cracks, comes
unstuck or goes hard.
(At least it exists in the UK. Most of the stuff I see on the net is
about caulk in America. Maybe you don't have it)