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.
The first step was to use "silicone II" to seal every seam of the durock including all corners being careful to smooth out all caulk to insure a clean glob free seal. Step 2 all the joints were taped with anti crack fiberglass backer board tape and skimmed with superflex thinset to insure no cracks form over the years.
The third and final step was 2 coats of "Redgard"anti crack paint on waterproofer one coat rolled on horizontally and one coat vertically .All corners are painted with a brush to insure proper sealing.There were as well inset soap boxes framed into the wall that were also caulked and then painted with the regard to complete the sealing process. The tile can now be installed in the showers with no worry of leakage or wood rotting for a lifetime of leak free showering !
All products used to completely seal up these 3 showers in Byfield mass are all available at Home Depot and can insure you never have any water damage in your home from shower leakage.Have your tile installer follow this process or do it yourself for total piece of mind when creating your new shower in your house . For a full list of other options and great advice on the many waterproofing options go here and check it out.
www.floorelf.com/preparing-a-shower-wall-for-tile
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
Natural Marble Bathroom Floor Tile 
