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ASTM C 406 - Standard Specification for Slate
This specification describes the material properties and physical requirements as well as the ways of sampling and testing. The following terms are defined:
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service life: the period of time over which it is expected that no replacement or repair is necessary due to weathering.
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ribbons: Narrow bands of carbonaceous material whch are darker in colour than the surrounding slate. Ribbons are supose to be inclusions of the original beds and are expected to be softer and less durable the the surrounding slate.
The classification of the roofing slates is as follows:
| classification |
min. Breaking Load
[lb oder N] |
max. Absorption
[%] |
max Depth
of Softening [in o. mm] |
| Grade S1 |
575/2558 |
0.25 |
0.002/0.05 |
| Grade S2 |
575/2558 |
0.36 |
0.008/0.20 |
| Grade S3 |
575/2558 |
0.45 |
0.014/0.36 |
The standard states that when comparing slate of same grade and equal thickness but from different sources, slates which meet the required breaking load at the lowest specimen thickness will yield the best performance.
The expected service life of roofing slates of different grades can vary, depending on the location and different environments and is as follows:
| classification |
Service Life (years) |
| Grade S1 |
over 75 |
| Grade S2 |
40 to 75 |
| Grade S3 |
20 to 40 |
Furthermore, statements about the appearance has to given:
- The commercial colour should be preceded by the words:
- "unfading" = colour doesn't alter
- "semi-weathering" = little alteration due to weathering
- "weathering" = alteraion due to weathering
Standard Roof: Sloping roofs utilising a nominal thickness of 3/16 to 1/4 in. (4.8 to 6.4 mm). The shingles should be rectangular unless otherwise specified. In addition, the shingles shall be drilled or machine punched for two nail holes which has to be located for proper headlap.
Textural Roof Sloping roofs utilising shingles in various colours, sizes, thicknesses and textures for architectural effects. The shingles shall be drilled or machine punched for two nail holes which has to be located for proper headlap.
Graduaded Roof Sloping roofs utilising shingles with a greater range of sizes, thicknesses and exposed lengths. The slates are arranged on the roof so that the thickest and longest occur at the eaves and gradually diminish in thickness and size towards the ridges. The shingles shall be drilled or machine punched for two nail holes which has to be located for proper headlap.
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