What is the difference between coal tar and asphalt?
They are developed from completely different sources. Asphalt is a product made from crude oil. Coal tar comes from coal, as its name implies. This means that even though these two products look and may even smell similar, they are very different. Asphalt has a higher softening point than coal tar. This characteristic makes it well suited for higher slopes, where it will solidify and should stay in place. Coal tar has a lower softening point, which allows it to actually flow on warm days. Coal tar can actually heal itself of minor cracks and punctures. This cold flow property is also why coal tar cannot be used on slopes above 1/2″ for organic felts, and 1/4″ for tar coated glass felts.
