We recently removed stacks of architectural precast sound wall panels that were resting on freshly cut oak timbers. The bottom panels all have a sticky, glue-like substance on their surface. Removing the substance by sanding or grinding will ruin the architectural finish. In addition, the panels are colored with an integral red oxide. Is there a chemical we can use to remove this substance without ruining the appearance of the panels?
According to Andy Baker, a chemical engineer at the United States Forest Products Laboratory, Madison, Wis., the substance on your precast panels is pitch, a resinous material excreted by trees to seal their damaged areas. Pitch will dissolve in both gasoline and methylene chloride. If trying gasoline, use a "clean" gasoline like the white gas used in camp stoves. This will leave less of a residue on the panels after evaporation. Clean the panels in an open, well-ventilated area, with no sources of sparks or open flames. Methylene chloride is an active ingredient in paint remover and can be found at most scientific supply stores. It is not flammable, but exposure to the fumes can lead to kidney disease or heart problems. Wear neoprene gloves when using it. Wear a respirator when using it indoors and read the warning label carefully. Gasoline and methylene chloride may discolor concrete. Use them first on an inconspicuous location to see the effect on the panels' appearance.