Sealers are frequently recommended for many types of tile. They range from sealers that stop water absorption to those that enhance the look of a tile. Many types of tile require sealing prior to being grouted, even if they need another coat of sealer afterward. Depending on the type of granite tiles being installed, this may be necessary; only some types of granite require sealing at all.
Why Seal Before Grouting
Grout is a mixture or Portland cement, water and pigments. When it is spread over the surface of a tile, a small amount may be left behind on the tile by the grout float. If a tile is porous, meaning that it absorbs water, it may absorb some of the grout. This can lead to the tile becoming permanently stained by the cement and pigments in the grout, or at the very least being very difficult to clean off when the grouting is done. Sealing the tiles prior to grouting acts as a "grout release." This keeps the grout on the surface of the tile, where it can be wiped off easily.
Granite is a natural stone material. What is sold as granite in the tile industry could, however, be any number of igneous stones labeled as "commercial granite." These stones could be Gabbros or Gneiss, as well as a few metamorphic stones. Therefore, not all stones sold as granite are created equal. Some are extremely dense and do not absorb water or moisture. Others are extremely porous and could potentially absorb large amounts of liquid and stains. Not all granites require sealing, but there are many that do.
Testing the Granite
To determine whether or not your granite requires sealing, take a loose tile or find an area of installed tiles that is unobtrusive or not easily seen. Place a small amount of water, a small amount of oil and a small amount of lemon juice on the tile and leave them alone for 10 minutes. After the 10 minutes are up, wipe the surface of the tiles with a soft cloth and look at the granite. If the granite has darkened where the water or oil sat, or lightened where the lemon juice sat, it requires a sealer.
Sealing Granite Tiles
While not every granite requires a sealer, sealers can help make the grout clean up go a little bit smoother and faster. If the tiles showed a need for sealing, or if you want to ensure an easier grout clean up, seal the granite tiles with a silicone-based, impregnating sealer. This colorless sealer will not affect the appearance of the tiles; it will simply fill any surface holes preventing moisture from penetrating the stone. The surface will look and feel identical to the unsealed tiles, but the grout will come off without drying into or onto the granite.