Spread a 1/2-inch-thick layer of fine grout over the entire surface of the exterior wall with a trowel. Apply the grout in an even layer.
Run a grout rake over the entire grout-covered wall to create a scratch layer.
Press the stacked stone veneer tiles halfway into the grout, spacing each stone veneer tile a quarter-inch apart. Grout will squeeze out in between the stone tiles as you apply them.
Scrape the trowel over the surface of the stone veneer tiles to remove any excess grout. Simultaneously, press grout into spaces that do not have enough grout.
Wipe off the surface of each stacked stone tile with a damp washcloth.
Slide your finger along each space between the stacked stone veneer tiles to smooth down the grout. Allow the stone tile-covered wall to dry for 24 hours.