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1. Black or chocolate-brown limestone impregnated with bitumen or natural pitch. Fine grit is added and incorporated at high temperatures, and the result cast into blocks. When reheated, the asphalt can be used as an impervious barrier to water, so is used as a damp-proof course and as a covering for ‘flat’ roofs.

2. Artificial asphalt is an inferior substitute, a mixture of tar with aggregates (such as sand and gravel) and pitch, unsuitable for waterproofing, but useful as a finish to road surfaces and walk-ways.


W. McKay (1957)

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