Reprinted from APOC

Water Soluble Residue from Asphalt Products     The residue, sometimes referred to as tobacco juice because of its color, is a normal result of the weathering of all asphalt based products, including plastic cements, coatings, shingles, base and cap sheet regardless of manufacturer. It has been happening for many years and intensive research has failed to find any ingredient or procedure that would eliminate the phenomenon, Fortunately, it requires a certain combination of weather conditions - intensive sun exposure, excessive night moisture, and prolonged lack of rain - and even then it does not usually reoccur after the first rainy season.     As most roofers have noticed, conditions this summer have been unusually bad. A heavy dew or fog dissolves the dry residue and causes it to accumulate in puddles on flat roofs, trickle down and stain a wall not protected by gutters or diverters, or discolor a light color shingle roof. The accumulation on flat roofs prevents a proper bond of coatings and must be hosed and/or scrubbed clean before coating. Extended residue accumulation can have a deteriorating effect on most roof surfaces if not occasionally hosed off. It certainly can cause aluminum and white acrylic coatings to peel. Although the residue formation cannot be prevented, the following steps can be taken to eliminate or minimize the unsightly runoff: Gutters and downspouts on low side roof perimeters. If parapet wall tops slope outward, are rounded, or have no raised lip on the outside edge, coping metal should be required. Hosing down residential or other small roofs at regular intervals during long dry periods of the first summer. Coating with solvent type fibered aluminum, over asphalt emulsion as soon as thoroughly dry, over plastic cement and other solvent vehicle asphalts after curing at least thirty days. Back to Economy Roofing's FYI