International standards for roofing slate
There are two main standards for roofing slate: The EN DIN 12326 und the ASTM which will be introduced here.
If one compares both it becomes obvious that the EN 12326 comprises considerably more investigations and tests to classify a roofing slate. The investigatons of the petrography, mineralogy and fabric are not included in the ASTM. Furthermore, no test for freeze-thaw resistance has to be carried out in the ASTM.
The assessment of the service life within the ASTM C 406 seems to me a kind of simplifying because processes of weathering and the corresponding behaviour of the rocks - no matter if slate or any other rock - is very complex. Due to this, its hard to make statements about service life only based of tests in the laboratory.
In my opinion the EN 12326 leads to more informationen of the properties of a (roofing-) slate and should be therefore preferred.