Laser cleaning of the Nickerson House exterior

The Smoke Nuisance, as it was referred to by the denizens of 19th-century Chicago, was caused predominantly by the burning of bituminous coal. As with many new buildings in post-fire Chicago, the Smoke Nuisance took a heavy toll on the exterior of Samuel Nickerson’s stately residence. Within five years of construction the building had darkened under a heavy layer of accumulated soot. By 2003, the exterior was covered in a black crust created by more than a century’s worth of pollution and grime. In 2004 CSOS Inc., an Illinois-based conservation group, was awarded the contract to clean the exterior of the Nickerson Mansion. During an 18-month period between 2004 and 2005, CSOS Inc. undertook the first restoration in the United States of an entire building exterior using laser technology.

During the late 19th century, bituminous coal was the preferred fuel for use in major urban centers such as Chicago. While the coal proved to be a cheap and bountiful source of energy, it was also exceedingly dirty. As with many new buildings in post-fire Chicago, pollution took a heavy toll on the façade of Samuel Nickerson’s stately residence.

The first through third floors of the mansion are clad in an extremely porous yellow brown sandstone from Berea, Ohio. Due to its porosity, the stone readily attracts pollutants.

Period photographs show that the exterior masonry had accumulated a heavy layer of soot within five years of construction.

By 2003, the exterior masonry was covered in a black crust created by more than a century’s worth of pollution and grime. A preliminary survey of the sandstone exterior was carried out in the fall of 2003.

The survey revealed that, despite its age, the sandstone masonry was in a relatively good state of repair. The survey did confirm that the accumulation of black soot was causing the erosion of decorative stone elements. Chemical analyses determined the black soot encrustation was a complex mixture of industrial pollutants. In certain areas of the accumulated layers of soot were found to be as much as 20 mils thick.

The most common and problematic deterioration was the visible chipping, spalling, and erosion occurring at the underside of belt courses and protruding stone elements.

The deterioration was caused by water infiltration at the exposed top of the stone that was then trapped at the bottom by the heavy soot incrustation. The trapped water would freeze and expand in winter conditions, causing the sandstone matrix to disintegrate. The deterioration of the belt courses and decorative stone was ongoing and accelerating. In order to prevent further damage to the sandstone it was determined that the soot encrustation would have to be removed.

Proposed cleaning processes were tested in October 2003 and March 2004. An area of the east façade that was fully enclosed within a light well between the Nickerson Mansion and the Murphy Auditorium was used for testing.

Mock-ups were completed using both controlled chemical cleaning methods and a laser cleaning system to remove the black encrustation from the sandstone exterior.