Pebbles to Use
Though you can lay a floor out of any type of loose rock, when choosing pebbles for a shower floor, you should select pebbles with fully rounded, soft edges. Stay away from pebbles with sharp edges to prevent the possibility of cuts from protruding pieces of the floor. If you want to simplify the process of laying the loose pebbles, consider using pebble sheets. While these pebbles come held together on a backing, making them easier to install than individual pebbles, the backing dissolves in the adhesive, which makes them loose pebbles once they're in the shower floor.
Installing Loose Pebble Floors
Before installing loose pebbles to a shower floor, put down a waterproof liner that prevents damage to the subfloor surface over which you intend to install the pebbles. Vinyl liners install flat against a floor's surface and are held in place with staples or adhesive. Once the floor is waterproofed, spread thinset mortar -- or the adhesive recommended by the seller of the pebbles -- to the shower floor and lay the pebbles in whatever design that you want in the adhesive. Use as much or as little space as you want between the pebbles.
Filling in the Spaces
After all the pebbles have been laid in the shower floor, allow the pebbles to dry in the adhesive for the length of time recommended on the adhesive packaging. As soon as the drying period has passed, grout the spaces between the pebbles to prevent dirt from accumulating between them. Apply grout with a grout float over the surface of the pebbles and remove all of the grout from the tops of the pebbles with a damp sponge before the grout has a chance to dry.
Maintaining Loose Pebble Floors
Like the adhesive used to install a loose pebble floor, the grout used to fill in the blanks must be allowed to dry for the recommended amount of time. Once the grout dries, apply a waterproof sealant over the pebble floor. This sealant prevents the grout from absorbing water, which can cause the grout to break down over time, and prevents discoloration from shampoos, soaps and body oils. With this step taken, loose pebble floors should need only occasional, minor cleaning with a mild soap.