On Nov 24, 7:37 am, Paul Franklin
wrote:

The whole point is to try very hard to keep the water *out* of the
wood behind the cement board. Since tile/grout and backer board are
not completely waterproof, you need a waterproofing membrane behind
them. Properly installed, any water that gets through the backerboard
will be stopped by the membrane and will either flow down the membrane
where it will eventually make it's way back into the shower pan (the
membrane should lap over the shower pan or mortar bed liner), or will
evaporate back out the way it came in, slowly over time.

Ahhh, but that's the part that is troubling me, if I understand the
"tile bible" correctly then I don't see how the water can make it's
way back into the shower pan (looking at the pictures in the book.)
If all along the bottom most row of tiles is caulked (between the
tiles and pan or tub) how is any water going to make its way back?
Obviously I am missing something. Unless it is supposed to make it's
way back into the pan "through the tiles and grout" - and as you said
- very slowly.

I want to fully understand this before I retile this shower. btw this
shower enclosure has a "one piece" 3'x3' or so floor. Not a
traditional pan with tiles etc. I'm not sure what type of laping it
has although I would venture a guess of "none."

Thanks!