Coal Tar Pitch Roofing Handbook - 1896 - Page 12
(To follow description of Concrete, which should be smooth and perfectly graded to carry water to outlet or gutter.)
Over the foregoing shall be laid a five (5) ply Coal Tar Pitch, Felt and Slag or Gravel Roof to be constructed as follows:
The Felt shall weigh not less than fourteen (14) pounds per one hundred square feet, single thickness.
The Pitch shall be the best quality of straight-run coal tar pitch, distilled direct from American coal tar, and there shall be used not less than two hundred (200) pounds (gross weight) per one hundred square feet of completed roof.
The Slag or Gravel shall be of such a grade that no particles shall exceed five-eighths (5/8) of an inch or be less than one-quarter (1/4) of an inch in size. It shall be dry and free from dust or dirt. In cold weather it must be heated immediately before using. Not less than three hundred (300) pounds of slag or four hundred (400) pounds of gravel shall be used per one hundred square feet.
The materials shall be used as follows:
First coat the concrete (A) with hot pitch (B) mopped on uniformly. Over the above coating of Pitch lay two thicknesses of Tarred Felt (C), lapping each sheet seventeen (17) inches over the preceding one and mopping back with Pitch (D) the full width of each lap.
Over the Felt thus laid spread a uniform coating of Pitch (E) mopped on. Then lay three (3) full thicknesses of Felt (F), lapping each sheet twenty-two (22) inches over the preceding one.
When the Felt is thus laid, mop back with Pitch (G) the full width of twenty-two (22) inches under each lap. Then spread over the entire surface of the roof a uniform coating of Pitch, into which, while hot, embed Slag or Gravel (H).
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