Black Magic

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Q: WeÕre trying to remove black roof cement from our row house ironwork. Is there a magic solution?A: As with any question about clean-up, the all-important first step is to establish what you have. Most likely youÕre stuck with bituminous cement, a generic term for a semi-solid mix of complex hydrocarbons. The bitumins used for over 100 years in roofing, coal tar, and asphalt look nearly the same but have different sources. Asphalt is derived from petroleumÑusually by processing but also through natural forcesÑso it will soften with petroleum-based solvents (kerosene, mineral spirits). Coal tar, on the other hand, is a byproduct of the coal industry and is far more tenacious. YouÕll have better luck freezing the stuff with dry ice, then chipping it off.

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