there can be nothing gained by leaving a void anywhere in a wet area, you should mind leaving a gap. its just an opportunity for water to penetrate in between the membrane and cement. BTW did u use cement to pour the floor or did u mean to say mortar? either way, i would fill it and then make sure i was very careful with the caulk and use GE ten year mold free, its awesome...i promise.

If you're tearing out the walls, then also tear out the floor. That is the major point of failure, and it makes no sense to try and save it. You need to learn how to properly construct a shower, because your drawings show several things that are big-time wrong. For starters, the liner needs to be installed on top of a mortar preslope, not a flat wood subfloor. The shower floor is then made of deck mud, not concrete, and it is also sloped, not flat. The backer board cannot be nailed or screwed through the liner at the bottom; the top layer of deck mud locks in the bottom of the backer board. I urge you to really research how a shower is properly constructed before you go any further.

Deleting duplicate post.

This post was edited by catbuilder on Mon, May 27, 13 at 12:40