The value of the deposit was obvious from the start, but the means of extracting the bitumen were not. The nearest town, Fort McMurray, Alberta was a small fur trading post, other markets were far away, and transportation costs were too high to ship the raw bituminous sand for paving. In 1915, Sidney Ells of the Federal Mines Branch experimented with separation techniques and used the bitumen to pave 600 feet of road in Edmonton, Alberta. Other roads in Alberta were paved with oil sands, but it was generally not economic. During the 1920s Dr. Karl A. Clark of the Alberta Research Council patented a hot water oil separation process and entrepreneur Robert C. Fitzsimmons built the Bitumount oil separation plant, which between 1925 and 1958 produced up to 300 barrels (50 m3) per day of bitumen using Dr. Clark's method. Most of the bitumen was used for waterproofing roofs, but other uses included fuels, lubrication oils, printers ink, medicines, rust and acid-proof paints, fireproof roofing, street paving, patent leather, and fence post preservatives. Eventually Fitzsimmons ran out of money and the plant was taken over by the Alberta government. Today the Bitumount plant is a Provincial Historic Site.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): For what was most of the the Bitumont plant's output was used for waterproofing?
roofs