Gauged and Ungauged - Slate

The terms gauged and ungauged have a specific relevance especially in regards to stone - and even more specifically - slate. Slate can be purchased either way and gauged is typically more expensive - for a reason!

Gauged has to do with the sameness of the pieces, and it particularly refers to the thickness. Ungauged slate I have seen vary in thickness from 1/8 inch to more than an inch from one side to another. Gauged vary as well, but typically stay in a variance less than 1/4 inch. The ungauged should be installed in a thick mortar bed to better regulate the evenness on the surface - like flagstone. Gauged may be installed in a thinset application.

But even gauged slate ought to be installed at a greater price, particularly for two reasons. Unlike ceramic, each piece must be cut on a wet saw; but in addition, there should be more care given in the installation to try to keep the surface as flat as possible. With the variation from piece to piece, and even within the pieces themselves, the installer has more of a challenge trying to keep the floor as flat as possible - and depending upon the consistancy of the gauged pieces, the task is almost impossible. But with more effort - and time - the results can be obvious.