Step 4. Apply mortar to each piece with a knife or popsicle stick, then press the piece lightly into place (shown at left).
Try to avoid having mortar ooze out from underneath. Leave enough room between the pieces for grout.
If tiles are different thicknesses, add additional mortar to the backs of thinner tiles until they're level. Let mortar dry for about eight hours.
Step 5. Mix grout according to package directions. (It should be the consistency of cookie dough.) Push in grout between tile pieces with a rubber spatula (shown at left).
Step 6: When all crevices are filled, let grout set for about 20 minutes, then use a damp sponge to remove any excess (shown at left).
Step 7. Allow finished project to dry for 24 to 48 hours; remove any remaining surface grout with a rag or, if necessary, use fine steel wool.