ghw wrote:
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).

TIA

Your "contractor" is lame! 1. Weight should not cause flex of the
joint. 2. Use caulk for wall/floor joins. Call him back and tell him
to do it right; follow up by putting the issues in a nice, business-like
letter and send it certified mail. That's so when it cracks for the
umpteenth time (pessimistically speaking), you have proof of the
condition and when it occurred.

The popular opinion is that corners crack, if grouted, because of
movement with expansion/contraction, so a flexible caulk is used.

Having cement board is not a reason to allow any moisture to seep behind
the wall! Jeesh!