Mark a horizontal line along the base of the wall, from end to end, using a level and pencil. Make the line at a height equal to the size of a tile plus ¼ inch. So if the tiles are 5 inches high, set the line at 5 1/4 inches up from the floor.
Make a vertical line through the center of the wall, from top to bottom, with the level and pencil, intersecting the horizontal line in the middle.
Spread tile mastic over the bottom of the wall with a notched trowel, from the horizontal line down to the floor and from end to end.
Press the bottom course of tumbled tiles to the wall, starting at the center and building to the sides. Put spacers between the tiles as you hang them. Cut the tiles at the ends on a wet saw to fit.
Spread more mastic across the wall, above the bottom course of tiles. Set the next course in place above the bottom course, again starting at the center and building to the sides. Repeat, working your way up the whole wall, putting spacers between all of them and cutting the end tiles as needed. Let the mastic set overnight.
Grout the whole wall, from top to bottom, using a grout float to press unsanded grout into the spaces between the tiles. Wipe off the excess grout with a damp sponge.