N is cupa s natural selection.
Grades of roofing slate.
S 1 will provide a service life of over 75 years s 2 will provide a service life of 40 75 years.
A standard grade slate cupa h selection will be less uniform and will require more sorting prior to use.
Slate grades are intended as a prediction of the slates expected service life.
It is truly the result of a craftsmen s.
This further highlights the traditional regional variations.
But the finished project will look as good if due care is taken of the slate grading.
According to astm test c 406 roofing slate falls into three grades of classifications.
Grade s1 slate has an expected service life of more than 75 years.
Welsh slate being very flat and smooth as well as a nominal 5mm thickness.
Grade s3 slate has an expected service life of only 20 to 40 years.
Roofing slates are rated through the american standards of testing and materials and given a slate classification from s 1 to s 3.
Greenstone slate is measured by eye to thickness and is then split by hand.
Grade s2 slate s service life is 40 to 75 years.