ASTM Roofing Slate Grading Explained

ASTM Roofing Slate Grading Explained

ASTM Roofing Slate Requirements


How does ASTM Requirments Apply to Roofing Slate?

The American Society for Testing and Materials (ASTM), is a free acting society, with the goal of keeping a high national standard for materials. The ASTM standards for slate are some what regulated by members of the National Slate Association (NSA) with members from leading american quarries.

This is a compleatly voluntary standard. Manufactures are able to send their products to ASTM labroratories across the country, thus making sure their products meet ASTM standards.

Roofing Slate ASTM Requirments (C406) can be read out here

Simply put, ASTM tests slate in three categories.

1) Breaking Load.
2) Water Absorption.
3) Depth of Softening.

Based on these three tests, Slate is put into 3 categories.

A. ASTM C 406 Grade S1: Expected service life in excess of 75 years.
B. ASTM C 406 Grade S2: Expected service life 40-75 years.
C. ASTM C 406 Grade S3: Expected service life 20-40 years.

Georgetown Slate continually tests our slate in approved ASTM laboratories in Dallas, Texas. Our slate meets all industry standards. For information and lab results, please email us at