I just finished an onyx backsplash in a kitchen with backlit slab onyx countertops. The countertops are solid honey onyx slabs with built-in LED lighting beneath them. The backsplash is 12 x 12 honey onyx tile installed on-point (diagonally).
Although onyx looks great when installed it is a very difficult stone to work with. Onyx is made up of bands of silicon dioxide, commonly known as quartz crystals, which fuse together into layers of translucent stone. This leads to varying striations of color and transparency throughout the stone. While cutting or fabricating bullnose (rounded) edges the stone is fairly brittle and has a tendency to literally shatter like glass. The most important tool to own while working with onyx is patience.
After letting the stone set overnight so the mortar could cure I grouted the backsplash with C-Cure brand “Macadamia” unsanded grout. Never use sanded grout with onyx or other fragile stones such as polished marble, the sand in the grout will scratch the surface of the stone. The grout will lighten as it cures and matches the base color of the stone almost perfectly. The grout lines will nearly disappear after the grout cures.
If you need an onyx installer in Fort Collins or Northern Colorado just give us a call. You may click on any of the photos below for a full-size version.