The most important part of shower construction and having a long lasting tile installation in a wet area is having proper waterproofing. Most of my shower construction relies on cementboard as being the tiling substrate for the wall. It is a very common misconception that cement board is waterproof. At best it can be called moisture resistant. That is to say that it will hold its structural integrity when exposed to water. However, it absorbs water at a very high percentage and will share the moisture it collects with whatever it is in contact with which is most likely framing.

Most porcelain tile has a water absorption rate of .5% and cement grout of around 10%. With a typical shower consuming at least 30 gallons of water, it is a guarantee that every time you use your shower, a substantial amount of water could be penetrating a non-waterproofed cementboard wall and being absorbed by studs. With the simple installation of a liquid applied waterproof membrane water will be 100% contained to only right beneath the surface of the tile and thinset. This adds up to a problem free shower that can completely dry between uses eliminating constant moisture. Showers constructed with a waterproof membrane are easier to keep clean and also will prevent cracks in the tile and susceptible grout lines as they have anti-fracture capabilities as well.

Bellow are some pre-tile installation pictures that show arguably, the most important part of a tile shower/bathroom.

 

Taped seams and screwholes ready for waterproofing.

Walls recieve 2-3 coats of waterproofing.  After pan cures it will be waterproofed with 3 coats. 

The last coat of pan waterproofing is dring in this picture. 

Divot filled, 100% waterproof and ready for tile.

Cementboard walls with 2 coats of redguard.  Waterproof Schluter Ditra was used as the floor substrate and all gaps and transitions on perimiter where sealed with 100% silicone.  The floor directly outside the shower can be a point of entry for water that is commonly overlooked.  Expessially on wood subfloors it is important to waterproof this area.

Picking out grout is more then just a color choice. Your basic $15 bag of grout can be referred to as a Portland cement based grout. I use this for the majority of floors and showers that I grout. Sanded and un-sanded are the two varieties of cementious grout. Sanded is for joints that are 1/8" up to 1/2" and un-sanded grout is reserved for tile that is spaced 1/8" or less. When the tile is spaced 1/8", I prefer to use sanded grout as the silica sand in the mixture makes it stronger.   

I recommend that all Portland cement based grouts be sealed with a penetrating sealer. This is a inexpensive and fairly easy process to do to help prevent staining and to keep your grout looking new. A penetrating sealer can be installed as soon as 48 hours after grout installation. It does not change the appearance of the grout. I prefer to use a roll on applicator to apply a adequate amount of sealer and wipe off the excess after about 10 minutes to avoid leaving residue on the tile.
 
Epoxy grout can be a great choice for many applications. The downside is cost. The material is about 5 times more expensive and installation cost are higher. The advantage to epoxy is a more stain resistant, impervious and stronger joint then basic Portland based grout. Commercial kitchens, countertops, high traffic areas and entryways are all a great place for epoxy. Epoxy has a unique smooth, plastic like appearance which makes it easier to clean as it isn’t sandy like Portland based grouts. It is a great replacement for un-sanded grout as it has a similar look with a much higher compression strength and stain resistance.

Another option is urethane grout. Starrquartz makes a premixed urethane grout which rivals epoxy in performance and price. It comes premixed and is easier to install then epoxy. It also has some interesting color choices.  I would recommend urethane grout over epoxy in residential floor installations.

Whatever type of grout you chose, know that it will appear cleaner if you match the grout color to the color of the contaminate that is likely to make the grout dirty. On floors, dark colors have the obvious advantage in camouflaging dirt. In kitchens oil based contaminants can be a problem and dark grout will show these types of stains less. In showers, I prefer to use light colored grouts as soap scum is less contrasting on the grout. If the grout color can’t be matched to the most likely contaminate because of appearance reasons, grout with a latex additive, urethane or epoxy will be a good choice because of there higher stain resistant capabilities.