Nail Holes

No slate should have less than two nail holes. The standard practice is to machine punch
two holes in all architectural roofing slate1/4" and thicker at the quarry and also in
commercial standard slate when so ordered. Four holes should be used for slates 34" or
more in thickness when more than 20" in length. Holes are punched from one-quarter to
one-third the length of the slate from the upper end, and 1 1/4" to 2" from the edge.
Where four holes are used, it is customary to locate the two additional holes about 2"
above the regular holes.
Some architects in the past specified that all nail holes should be drilled and countersunk.
On normal thickness slates, no method of drilling has been developed which will produce
the same clean hole as by machine punch- ing, because the small thickness of stone at the
cutting point is insufficient to absorb or dissipate the drilling force. Hence the industry,
through the Association, in 1923 adopted the machine punching of nail holes as standard
practice.
That the results are excellent is demonstrated by the fact that, when given two slates with
holes punched by either method, architects have usually selected the machine punched as
the better and have even called them drilled and countersunk.
Machine punching is preferable to hand punching. The term hand punching usually refers
to the use of the double head slaters hammer having one head in the form of a long prong.
Machine punching may be done either at the quarry or on the job. Hand punching of

holes in fitting hips, etc., is, of course, necessary.