Protecting the Tiles From Damage

• Ceramic tiles come in a variety of styles, from clean, machine-made designs to rustic, handmade tiles. While some of the tiles may appear to be square, or straight edged, in fact most ceramic tiles are at least slightly irregular in size. In the case of some handmade varieties, they may be extremely irregular in size. Butting ceramic tiles up against one another with no grout joint will cause these irregular edges to butt against one another as well. Over time, as the house settles, these irregular edges will wear against one another, cracking or damaging the tiles.
  
  

Creating Straight Grout Joints

• Ceramic tiles are most often made of slip, or wet clay. When they are dried, they change shape slightly depending on where they are in the kiln. Some may shrink more than others, making some tiles in a box a millimeter or two smaller than others, which may not seem like a lot, but butting the tiles against one another with grout lines will cause the lines of tile to move in irregular patterns, rather than lining up straight. Grout joints make up the difference in tiles sizes, allowing you to open and close the joint slightly to keep the rows of tile straight.
  
  

Water Resistance

• Whether the ceramic tiles were to be butted against one another or left slightly apart, there will be space for moisture to seep between the tiles. Ceramic tiles are water resistant, but this gap would allow water and stains to get behind the tiles, which may cause the clay body of the tile to stain from behind, discoloring it, or it may eat away at the mastic, loosening the tiles from their foundation. And moisture seeping between the tiles may cause mold, rot or mildew to begin to work its way into the substrate. Grout keeps moisture out, making the entire installation water resistant.
  
  

Stains

• While grout itself may discolor over time, a space left by two ceramic tiles, no matter how tightly they are butted, will still fill with debris even in dry areas. Many ceramic tiles are angled inward on the top edge just slightly to give a tighter grout joint. So even if you could butt the tiles together, you will have a space remaining between the tiles. This space will be much smaller than a standard grout joint and therefore more difficult to clean if food particles, wine or mud were to work their way into it. Grout may be porous, but it is easier to clean than a crack.