Just had a new shower installed, tiles going down and overlapping the
flange of an acrylic shower base. Contractor "sealed" the tile/base
connection with grout, which soon cracked due to weight in shower and
flexibility of base. I then used grouted caulk, which now has also
cracked.

How can I seal this small gap in a way that will not crack? Or maybe I
should not worry about it (concrete backboard behind tiles).


*That shower pan should not flex. There should have been a small pile of
cement put down and then the pan pressed down onto it. The short term
problem is what you are experiencing now. The long term problem is that the
pan will eventually crack.