Every masonry cleaning project presents a unique set of conditions that call for unique solutions. Three masonry cleaning jobs underway in the last few years demonstrate the great challenge cleaning dirt off old masonry can pose. SAINT JOSEPH'S CHURCH, DENVER Paint can hide a lot of things. At St. Joseph's Redemptorist Church in Denver, it was hiding almost 60 years of dirt. Officials decided to strip away the paint to restore the church to its original appearance. A proprietary, potassium hydroxide-based paint stripper was used to dissolve the layers of oil and latex paints. Workers brushed the alkaline paint stripper on by hand and then let it soak overnight. The cleaning crew rinsed off the dissolved paint and paint stripper with hot water sprayed at a pressure of 800 to 900 psi. Because some of the paint on the church contained lead, the contractor couldn't flush the runoff water into city storm sewers. TRINITY CHURCH, NEW YORK CITY Trinity Church in New York City also is blackened by pollution, but that's not why it's being cleaned. Needed repairs can't be done until the encrusted dirt and soot are removed to permit careful inspection. The site itself had major access problems. Sitting at the head of Wall Street in Lower Manhattan, Trinity is surrounded by giant neighboring buildings. The tunnel effect these tall buildings create can generate 100-mph, hurricane-force winds. A sophisticated scaffold system had to be designed to clean the church's 165-foot tall steeple. FIELD MUSEUM, CHICAGO Although carbon deposits and acid rain did a great deal of damage to the stone, the staining was less extensive than at St. Joseph's or Trinity. Only badly soiled areas of the facade were cleaned. These included the eaves, overhangs, cornices, and other areas that rainwater couldn't reach and clean naturally. Water soaking was selected as the gentlest cleaning method that would be effective.