Pebble tiles provide a unique look. Like most mosaics, they are comprised of lots of small pieces conveniently adhered to a mesh backing material. This makes the installation possible without the mind numbing process of setting a gazillion individual stones by hand. Most tile sheets are “keyed” so the installation interlocks from sheet to sheet but still gives a nice uniform but random look. Depending on your installation, most of these tiles can be set without much need for actual tile cuts. The random patterns can be rotated and the sheet’s backer cut with a simple utility knife. Individual stones can be removed or placed to customize the fit.
Thin set or mastic?
Because the pattern of pebbles is variable, I like to dry fit as much as possible before I begin the setting process. This is a time consuming task and it is very difficult to rush.
A good majority of pebble installs are on shower floors. Like a more traditional mosaic, these mats can easily conform to a sloped or drain-pitched concrete bed or built-up drain pan. While the use of mastic is a fine alternative for backsplashes and low moisture environments, the shower floor requires a really durable product like cement based thin set.
Another reason I like to dry fit ahead of time is thin set only has a fixed “pot life” and once it starts to become too stiff the installation becomes more problematic. Rushing a pebble tile installation will only lead to poor results. For pebble tiles to look and feel good (the rounded stone tops act like little foot massagers) the install depth needs to be just right. The size of the stones will vary but most like to bed about 1/8” deep. If a small amount of thin set oozes up through the mesh backer you will get a great long lasting and secure bond. If a lot oozes up then the thin set is competing with the “grout zone”.
Sanded grout is what you need
Sanded grout is used when grout lines exceed 1/8”. These pebble mosaics by their very nature have grout spaces that exceed that dimension a few times over. To maintain the desirable bumps of the pebbles, the grout needs to be applied at a depth that allows the stones to assert their personality.
When I grout for these parameters I like to work in smaller areas so I can stay on top of the grout clean up, just like when working with thin set grout has a limited “pot life” and when it starts to become stiff the ease of workability does down. Most grout cleanups are done pretty dry, with a grout sponge that is barely damp. When working with pebbles a wetter sponge will allow you remove a bit more of the grout to maintain the profile of the stones' bumps.
Simply running a grout float over the stones and doing a quick wipe with the sponge results in a pretty flat and smooth surface…but if you wanted flat your should not have spent all of that extra money on the pebbles.