Hi;

I'm laying tile in a second floor bathroom. There is an OSB sub-
floor. I put 1/4 inch backer board (Hardi) down on the sub-floor and
used thinset and screws to attach it down. I haven't started tiling
yet.

Prior to this there was just carpet over the OSB sub-floor, and we had
a small mold issue at the shower; water drips when we open the shower
door and it soaked through the carpet and got the OSB wet and there
was some mold growth on the carpet there and the sub-floor.

I cleaned up the mold very thoroughly before laying down the backer.
There is an 1/8 inch gap between the shower pan edge and the backer
board, and I'm worried that moisture will get in there as it did
before.

I read somewhere, but I can't find it again, that I can/should put a
bead of silicone between the backer board and the shower pan to seal
off the possibility of water getting in there. Then, I'll have tile
over that, with another caulk bead between the tile and the shower
pan.

Does this make sense to do? If so, what kind of caulk should I use
between the backer board and the shower pan? I think I would use GE
Silicone II.

Comments appreciated.