Met History wrote:

> Do I recall this correctly, or was it some sort of cruel joke,  that
> slate really does season out and has to be replaced, because it
> becomes so brittle that even mild weathering will make it fail?

C,

In my experience, which is limited, the reason for slate failing is not
that it becomes brittle but that it becomes soft and "punky". I believe
that it is due to many many years of saturation and freeze-thaw cycling
that the laminations of the slate begin to delaminate, though on a
magnifying glass level, and that eventually the slate fails. There is
also the issue of micro-cracks and stresses that may have occured either
through original installation, too much of a setting of the nail head
with the hammer and/or walking/working on the slate or the impact of
falling objects such as tree limbs, meteors etc. that may not show
and/or cause failure for many years. A good test is to take you
pocketknife, as every American boy should have one, and without opening
it use the butt to tap on the slate. If the slate rings then it is good.
If it goes thud thud thud then call Joe Jenkins and he, who has a lot of
experience, will tell you what is true.

][<en

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