There are few types of stone more puzzling to homeowners and new installers alike than ungauged slate. While most stone tiles have a definite top and bottom that are easily distinguishable from one another, ungauged slate tiles can be installed with either side facing up. In addition to this, the thickness of these tiles can range from 1/8-inch to 1/2-inch between tiles or within one tile, making the installation more difficult and time consuming. There are several things that can help make the installation go more smoothly, however, ensuring that the finished installation looks exactly how it is meant to.
Most types of ungauged slate are not only highly variable in thickness and texture, they are also highly variable in color. It is not uncommon for some pieces of stone to be one color on each of the two sides, however. Therefore, a dry layout is important to mix and blend the colors of the stone evenly over the entire area. If a piece of tile has a color that is truly out of place or unacceptable to the homeowner, it can often be turned over and installed with the other side facing up.
During the dry layout, care should also be taken to spread out the tiles according to thickness as well. Tiles that are very thin on one side and very thick on the other should be used as cut pieces on the edges of the installation to help make the final results smoother.
The tiles should be lifted from the dry layout in the order they will be put back down. This will help ensure that the thickness differences can be dealt with correctly. After the thinset has been spread onto the substrate, additional thinset should be backbuttered onto each piece of slate with more thinset being put on the thin areas of the tiles and less being put onto the thick pieces. When the tiles are beaten in, this backbuttering smoothes out the installation and levels it.
Ungauged slate may be a little startling when it is first encountered, but when care is taken, beautiful installations can result.