After you have installed the tile over the top layer of your shower floor, you will be left with visible joints that will need to be filled in order to reduce the access of moisture to the layers below. These joints are filled with grout, which is a liquid form of concrete that is pushed into each individual space between each piece of tile. The grout serves two purposes, first it is a cement based product, which will adhere to either side of the tile, and second it will reduce any minimal mis-leveling from one tile piece to the next.
Cement Based Grout
There are two types of grout, sanded and un-sanded, both of which use a base of Portland cement, but used under different conditions. If you choose to install your tile with the minimum industry width of 1/8 of an inch, it is recommended that you apply an un-sanded grout, which consists of Portland cement and polymer additives, which help support increased flexibility. Un-sanded grout will have a runny consistency and will be easily smoothed over into each joint opening. In the event that your grout widths are greater than 1/8 of an inch, it is recommended that you apply a sanded version, which contains a Portland cement base, sand, and polymer additives.
An alternative to cement based gout, and where conditions are harsher, such as high traffic areas, is an epoxy grout that is made primarily of a resin and hardener. Just like the cement based grout, the epoxy grout will have two versions, sanded and un-sanded. The epoxy grout has an added benefit of resisting chemicals and stains, which over time, may occur in your tile installation. Further care needs to be taken for natural stone tiles, due to their porous nature, they will need to protected by a sealer prior to any grout being applied. Epoxy grout is not a common grout choice for a tile installation over your shower floor, but you will need to determine if it is best for you.
The grout you choose to apply between the joints of your tile installation will need to be sealed, since grout is porous, it will allow the entry of moisture. There are varying sealers that can be applied over the grout, all have their specific requirements. The common theme is to ensure that you allow the grout application proper curing time before applying the sealer over it. The next rule is to allow the sealer the proper amount of time to cure over the grout. Following the grout and sealer manufacturer suggested wait times will be imperative to having an effective tile installation. It is important to also not run the shower inside your built up shower pan before a proper sealant has been applied to the grout and allowed to cure, moisture seepage does take time to evaporate, and any residual moisture may impair the effectiveness of the sealant or worse cause discoloration of your tile installation.