After a century of deterioration and a thick coat of coal soot, the buff Arkosic sandstone of the First Presbyterian Church of Decatur, Ill., was due for a cleaning. For several decades, the church had been exposed to soot from hundreds of steam locomotives, and acid rain intensified the damage. A century of freeze-thaw cycles also had contributed to the sandstone's erosion To prevent further facade damage, restorers had to remove the greasy soot, replace badly eroded stone, tuckpoint the entire area, and treat it with a silane-based consolidant to strengthen the sandstone's bond. The greasy carbon-deposits coating would be difficult to remove, and the fine, friable sandstone needed to be treated carefully to prevent further damage. Workers tested various detergents alone, and with bleach and water, and muriatic acid and water additions. When the solutions didn't work, the restorers tried a slightly abrasive cleaning system--low-pressure, wet-aggregate cleaning. This method is significantly safer than dry abrasive techniques. It also substantially reduces the amount of airborne dusts, making it suitable for use where dry abrasive cleaning is forbidden. Keywords: coal soot, pressure-washing, substrate