If this will be a shower wall that continually gets wet, you need a waterproof membrane.
Glue does not cut it for the pro's, and many pro's don't follow the advice of the big box store.
It needs to be waterproofed or you will have issues in the near future, I guarantee it.
Just tryin to help you out,
Oh, someone else had this same issue...and let it all out.Gossip Rocks Forum