These pictures give you a bit of an idea whether your dealing with a coal tar pitch built-up roof instead of an asphalt built-up roof.
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Note the ripples where the material is on a vertical surface. Asphalt would harden completely and would not develop ripples like this.Over time, the gravel surfacing on a coal tar pitch roof tends to sink into the coal tar pitch, making the roof look darker than an asphalt built-up roof would at the same age.What kind of roof is it, coal tar pitch or asphalt? A quick test will show you: put a small piece of the roofing material in lighter fluid, wait a few minutes, and you’ll have your answer. The coal tar pitch (on the left) turns the fluid a bright yellow-green, while the asphalt turns it brown.
