How to Install Window Sill Tile

Measure under the sill with a tape measure and mark the wall at the length of a tile. Extend the line so it's parallel with the bottom horizontal span of the window, using your level and pencil.

Fold a piece of sandpaper into a small square, and use it to buff the wall between the bottom of the sill and the line (the area where the tile is going).

Mark the middle of the horizontal section. Spread tile adhesive on the back of a bullnose tile and press it to the wall on one side of the mark, with the bullnose finished edge facing downward. Set a second tile next to it, on the other side of the mark, in the same fashion. Put spacers between the tiles as you set them.

Hang the rest of the bullnose tiles in a row along the bottom of the sill, from the middle working outward. For each one, spread adhesive on the back and set it in place on the wall with spacers between them. The finished bullnose sides should all face down, forming a horizontal border for the wall. Set all the full tiles that will fit before the corners of the window on either side. Let the tiles set overnight and pull out the spacers.

Apply painter's tape on the wall around the tiles, so the grout doesn't stain the wall. Spread grout over the tiles with a grout float, pressing it into the lines between the tiles. Wipe off the excess grout with a sponge.