Table 1.Summary of technical details on four cleaning techniques selected during first phase of this study.,,

Symbol,Description,Comments

WW,Water wash,Hose pressure.  Not useful as a cleaning or rinsing method.

PW,Power wash,"Water delivered at approx 100 to 600 lb/in2 pressure, depending on standoff distance, "

,,"tip of wand to stone surface.  Effective on protected areas, such as the pilaster to the south of the window at the top-platform level; not effective on exposed areas without aid of detergents.  Streaks of clean stone appear when tip is held close to surface.  Danger of damage to stone when tip is used in this manner.  Effective as a rinse."

ST,Steam,Deliver at 80C at approx 150 lb/in2 pressure.  Uneven results.  Difficulty experienced in 

,,delivering even flow.  Streaky.  Less effective than PW.  Note problems with cold weather on 3/16/95 and problems with equipment.

ADC,Alkali detergent liquid concentrate,"pH 10.6.  Brush-coat dwell time, 10 minutes.  Even cleaning when followed by PW at the "

,,"top-platform level, but not as effective as ADG.  Not effective at the second-level frieze."

ADG,Alkali detergent gel,pH 9.7.  Gel left on 10 to 15 minutes.  Even cleaning when followed by PW at the top-

,,platform level.  Easier to use than detergent in liquid-concentrate form.  Not effective at the second-level frieze.  G.S. Wheeler thinks ADG/PW is the most practical general cleaning system if a water-based cleaning technique is selected but that approx 20 percent of the surface will have to be recleaned by other techniques.

ACH,Alkali gel with chelating agents,"pH 8.5.  Potentially more aggressive than detergent solutions, produced a spottier "

,,cleaning than detergents on the top-platform level but was as ineffective as the detergents on the second-level frieze.

APW AR,Alkali prewash/acid rinse,A two-step system.  The alkali pretreatment sits on the stone for 30 minutes and then is 

,,"rinsed off.  An acid cleaner is then applied for 3 to 5 minutes and rinsed off.  When used with PW, this technique produced very clean surfaces.  Problems include a rough, etched surface appearance, likely removal of stone, and potential chemical residue in spite of rinse."

Misting,Filtered water,Delivered as a fine spray from a series of nozzles and played over the stone from 4 to 24

,,"hours.  This technique works by dissolving gypsum crusts.  Problems are that it is time consuming to control so that maximum cleaning is achieved without removal of marble from weakened substrates.  Also, more water can enter the building by this technique than as a result of any other water-based cleaning technique tested."

Thomann-Hanry ,---,An abrasive cleaning technique using a proprietary mixture of glass particles (5 to 50 

process,,"mm) and aluminum silicate crystals, delivered at very low pressure (approx 30 lb/in2).  Gypsum crusts and soiling layers are removed from the surface.  The method is fast and produces an even, clean appearance that is less rough than APW/AR and possibly less rough to the touch than detergent-cleaner/PW techniques.  Main advantages are control, absence of water, smoothness of finished surface, and effectiveness."