It is partly because granite countertop tiles are milled to represent the smooth look of stone, granite tiles are designed to lay close together. To create this look, granite countertop tiles, as they are installed, are to be separated by only 1/16 inch. The standard tile spacing is at least twice that space—1/8th inch. Sometimes it is ¼ inch. This more narrow spacing requires the use of a different type of grout and a different type of grouting, such as that you'll see below.
Laying the Tile on Mortar
Spread your thinset mortar in a thin layer, using a notched trowel. To keep the mortar from seeping up into spaces between the tiles, make sure the mortar is thin and is void of lumps or mounds. Lay the tiles on the mortar. Insert spacers between the tiles. Push the tiles together until they are tight against the spacers. If there is any mortar on the face of the tiles, wipe off. Remove the spacers, and allow the mortar 24 hours to set before you proceed with the next step.
Mixing Your Grout
In a bucket or large container, mix unsanded grout and water. Stir the mixture slowly, by using a stirring stick or broad putty knife. Stirring too fast can create air bubbles in the mortar, so avoid using a power mixer. After the mortar is thoroughly mixed, allow 10 minutes for chemicals in the grout to activate. Before applying the grout, stir it once more.
Applying the Grout
To your tile surface, spread the grout with a rubber float. Apply to small sections, one at a time. The idea is to force the grout into the spaces between the tiles and that the top surface of the grout is level with the top surface of the tiles when you finish.
Cleaning the Tile
Each time you have grouted one section of the tile, proceed to the next section, allowing the first section to sit for one or two minutes. Then, use a moist sponge to wipe away any grout left on the tile surface. Be careful to avoid disturbing or reducing the grout in the tile spaces. When you're finished cleaning the tiles, check to be sure the grout in the spaces is still level with the tile surface. If necessary, re-grout where the grout has been reduced.
When you have finished with all tile sections, allow the grout to set for about one hour. Using a slightly damp, clean sponge, wipe the tiles to remove any grout film or haze. As the grout dries, wipe it again several times with the damp sponge, until the haze has been completely removed. After 48 hours, the tile and grout should be fully set and ready to use.