In ,
ghw typed:
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

GE pure Silicon caulk is made for just that purpose. Get the gaps well
cleaned and even rinse some denatured alcohol down thru them (with exhaust
fans on FIRST), to caulk will adhere the best. Silicon caulk is a tad
expensive, but never hardens, allows pieces to move around without losing
the seal, and seems to last forever. I pull apart some pieces once that had
1/4" beads in it; it was still perfectly adhered, still very flexible, and
was still doing its job; this was 18 years after I put it down, too.
Make sure it's silicone; those with just a % of silicone still allow it
to harder after a few years and don't do nearly as good a job. Any good
hardware or home store seems to carry it.
It stinks while it's curing, comes in clear or white and sometimes other
colors. "Clear" isn't really clear; more like a faded window covereing.
There's sometimes a temptation by some to use it as a glue; don't! Since
it's so flexible, it'll still "run" over time and stretch thin between two
movable or widely separated parts. I love the stuff. No monetary interest in
it, but I do wish I'd bought some stock in it! g

As for small/tiny leaks: They still should be fixed. They're a home for
mold, just waiting for it to move in. You want to be careful of creating
places mold can get into; it can be VERY expensive once it gets to the point
of making people sick. Well IF it gets that far; it's not a given or
anything but best not to take chances.
Oh, and all shower/tub enclosures I've seen in the last few years say to
use the Silicon caulk, too. To keep it from sticking to your fingers, dip
them in cooking oil; works great! Don't get it on your clothing; it'll never
come out.

HTH,

Twayne`