Pebble tile is a conglomeration of polished and sanded stones or pebbles attached to a flexible substrate. The substrate squares are treated like regular tiles and glued into place using a tile adhesive. After the adhesive has set, the grouting can begin, but because of the irregularities in the size and shapes of the pebbles, grout needs to be applied in a totally different way than with normal tile applications.
Seal the pebble tile after the adhesive has completely dried. This action will prevent the pebbles from absorbing the grout colour. Allow the sealer to dry.
Dip your grout float into your grout, and apply it to the pebble tiles by pushing it into the spaces between the pebbles. Work slowly when doing this to fill in all cracks and crevices. When you have finished, the entire pebbled area will be literally covered with grout.
Allow the grout to set up and dry for 20 minutes.
Dip your sponge in the bucket of water and wring it out until it is damp. Begin to wipe away the grout on top of the pebbled area. When the sponge becomes full of grout, rinse it by dipping it into the water bucket.
Completely clear off all the grout from the surfaces of the pebbles, but don't wipe hard enough to remove any grout from the spaces between the pebbles. Allow the grouted surface to dry for 24 hours.
Apply sealer to the grout and pebbles.
For a bit less hassle, use a pre-mixed grout instead of a type that needs to mixed precisely with water. This will save a little time, as you can just opened up a pre-mix container, dip your grout float into it and begin grouting.