Your shower may sparkle with gleaming ceramic tiles, but what's holding those shiny squares together? Believe it or not, it's cement. Most grout is composed of a cement-based material that works to seal those tiles together and keep any water from seeping through. It's important to use the correct type of grout in a shower or water damage could occur behind the tile. After tiling and applying grout take the extra step of sealing the grout joints with a water-resistant grout sealer.
Standard grout, sometimes called cement-based grout or Portland cement-based grout, is available in powdered or pre-mixed form as well as in both sanded and unsanded varieties. This is the kind of grout most commonly used for do-it-yourself projects as it is clean, water-based and easy to work with. If your joints measure 1/8 inch or larger, you should choose sanded cement-based grout, while if your joints are smaller than 1/8 inch, unsanded cement-based grout is a better choice. Cement-based grout is the type of grout most commonly used on shower tile joints.
Resin grout is alcohol-based rather than water-based. Because of this, it is very resistant to chemicals and requires more complicated installation procedures. Unless you're planning on conducting chemistry experiments in your shower, resin grout is probably not the best choice for your shower grout needs.
More costly than cement-based or resin grout, epoxy grout is water and stain-resistant. It is primarily used in situations that require a larger degree of resistance to stains, like kitchen countertops. Epoxy grout can be more difficult to find than other types of grout. While the water resistance it offers may seem tempting, epoxy grout is not often used in shower tiling.
Cement-based grouts are also available infused with polymers like silicone or latex. These modified grouts are comparable to standard cement-based grouts, but offer the added bonus of increased water resistance due to their polymer content. These modified grouts are becoming more popular in shower tiling, but are more expensive than standard cement-based grout and do not offer the same variety of colors.