Discussion
Due to coal tar’s natural resistance to water, it may be utilized in the construction of built-up roofing membranes that will be expected to hold water over long periods of time. When applying a membrane that is required to hold water, follow Specifications 220, 420, or 920 for applications over non-nailable decks (four plies of Tarred Organic Felt, Tar-Glas or Premium Tar-Glas Felt set in solid mopping of coal tar).

NOTE: The base sheet alternate shall not be used.

When the roof is water cooled or has been designed to be continuously wet, the top surfacing of pitch and gravel must be applied as follows:
  1. Pour over the entire surface of the roofing membrane, a uniform coating of Coal Tar, not less than 70 lbs. (31.8kg) per 100 (9.3m2) square feet. While hot, apply not less than four hundred (400) pounds (181kg) of gravel or three hundred (300) pounds (136kg) of slag for each one hundred (100) square feet (9.3m2).
  2. All loose gravel or slag shall be swept from surface and a second uniform pouring of not less than eighty-five (85) pounds (38.6kg) of coal tar shall be applied over the gravel or slag, into which, while hot, shall be applied a second layer of three hundred (300) pounds (136kg) of gravel or two hundred (200) pounds (90.7 kg) of slag for each 100 square feet (9.3m2). For water retaining roofs, the entire surface shall then be thoroughly broomed free from all loose gravel or slag. It is advisable to roll the finished surface with a light roller so that aggregate is thoroughly embedded.
  3. Use Flashing Specification 110P available from your Koppers representative.
NOTE: Roofs equipped with controlled flow drainage systems do not require the extra top pour and gravel application.
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