ASTM C 217 -09- Weather Resistance This test method is useful in indicating the differences in weather resistance between various slates. This test method also provides one element in the comparison of slates. The difference between the longevity of S-1, S-2 & S-3 slates is significant and this is an excepted method of that determination and should be a major consideration in the selection of a premium roofing slate. The C 217 standard defines the depth of softening as an exp