Slate is a form of rock that formed from a sediment that dates back approximately 300 million years. Over time, layers of sediment bound together as they were heated by geothermal activity until they eventually lay so closely together they formed into rock.
“The interesting thing about these original layers is that they still remain when the rock is quarried, and it is this that allows slate to be so finely and evenly split,” Macmillan Slaters and Tilers’ Jarrod Gillespie says.
Determining the Quality of Slate
“That’s how you can tell a good quality slate from a poor quality one; it’s in the layers. A good quality slate will split evenly across the whole slab whereas a poor quality one will vary in thickness.”
Using a poor quality slate can be disastrous, primarily because it is a premium product with an associated price tag. “If you use a poor quality slate, when it is laid, it won’t be flat and it can cause aesthetic or waterproofing issues because of the size inequality,” Jarrod says.