Kitchens.com The homeowner, aka Mr. Beal, responds as follows:

"The tiles are 4x4 inch slate and since slate is not perfectly square, I set the tiles as close together as possible, making sure I stayed on the layout lines so that I didn't lose level or plumb. Where I needed to, I used small finishing nails to hold the tiles in place. Since the grout line was anywhere from 1/64 inch to slightly more than 1/8 inch, I used an unsanded grout.

"The grout was manufactured by TEC and the color was 941 Raven. My suggestion if someone is going to do the same is to pick a grout color that matches the darkest of the slate being used so the grout does not "picture frame" the tiles. You do not want the grout lines to stand out. Hope this helps."