In my 30 year career I've repaired and seen hundreds of showers that had water damage both inside the shower and inside the wall. Many times the mildew had eaten away at the wood studs in the wall and caused the grout to turn black from the inside out causing costly repairs and complete tear outs to redo the wood studs.In severe cases mildew can be dangerous to the health of the elderly and the very young. The following "how to" will explain the most economical "ultimate shower waterproofing " technique to insure a "never leak shower" and insure a "no mildew" tile installation. There are other options out there but this is by far the most economical sure fire way to know you will never allow water to penetrate your shower walls.
I am currently working on this job in Byfield mass. and all the walls and floors will be slate and marble finished.The contractor on the job was responsible for installing all the backer board and The contractor used durock on all the inside shower walls not Hardy board as I would have preferred. ( see my blog "hardy board vs Durock) When the home buyer called me to get a estimate he voiced great concern about waterproofing his shower walls so as not to have mildew or water damage in his shower walls ever. Since durock was already installed in all the showers and not hardy board it was required to completely seal every sq inch of the shower walls as well as seal all joints to insure no water ever got to the wood studs in the wall.
Pictures below are as follows left to right in order. 1-Silicone II caulk product, ,2- Redgard waterproofing crack supression paint on sealer product,3- Marble and granite modified thin set product, 4-Durock taped and thin setted, 5-Durock sealed with Redgard6-,Inset soap box caulked and Redgard sealed, 7-Floor Durock redgard sealed 3 ft out from wet area