Do window cleaners use soap?

Glass Technical Paper FB01-00 records two methods, and they land on opposite sides of this question.

The routine method starts with the solution. NGA's paper says cleaning "should begin by soaking the glass surfaces with clean water and a mild, non-abrasive glass cleaning solution." The pure water technique starts with the water: NGA records it as "an additional glass cleaning technique" the International Window Cleaning Association recognizes, with pure water delivered to the glass through a specialized extension pole and held to 20 parts per million or less of total dissolved solids. NGA's description of that technique names no cleaning solution.

In the routine method, the solution goes on generously and comes off completely, in that order.

NGA says to "Apply generous amounts of solution to the glass surfaces with a brush, strip washer or other non-abrasive applicator, and lightly agitate to loosen the soil and debris," a step the service page's method section sets in its full order. A strip washer holds that solution in a fabric sleeve on a T-bar handle, the part defined on the scrubber sleeve glossary page.

Two limits bound what that solution can be. Among NGA's own DO NOT items is using abrasive cleaning solutions or materials for maintenance cleaning, and NGA says "Glass cleaning solutions should not include acids, especially muriatic / hydrochloric and Hydroflouric." Then, immediately after the solution goes on, NGA has a window cleaning squeegee remove all of it.

The second method's description has no solution step in it.

As NGA describes the technique, pure water reaches the glass through a specialized extension pole, a non-scratching (non-abrasive) brush agitates it, and a final pure water rinse follows that is generally allowed to evaporate. The water for both the wash and the rinse must be at 20 PPM or less of total dissolved solids, treatment by ion exchange or reverse osmosis should be used at all times, and tap water is not acceptable. At no point in that description does NGA name a detergent or a cleaning solution.

So the answer turns on which published method is meant: one calls for a mild solution, and the other describes treated water alone.

Two kinds of glass move the word mild somewhere stricter than the routine baseline.

For laminated glass, NGA says "do not use anything that is corrosive such as solvents, acids, bases or other chemicals." Its longer list of materials that may harm laminated glass, which NGA says is not exhaustive, belongs to the answer on whether impact windows are cleaned like regular windows.

For glass with applied film, NGA recommends "Mild detergent or household window cleaning solutions" and says cleaning solutions containing ammonia "may not be suitable for all film types," sending that choice to the film supplier. The rest of that question is on whether window film can be damaged by cleaning.

Two neighboring questions take over from here: what lifts the solution off, answered on whether a squeegee is better than a cloth, and what abrasives risk, answered on whether window cleaning can scratch the glass. Among NGA's own DO items is to "be aware of and follow the glass supplier's specific cleaning recommendation," which is where the cleaner for any particular pane is settled.