In recent years, as a result of contaminated or defective surfaces on some tempered and heat-strengthened glass, construction window cleaners have been exposed to new challenges and unforeseen liability in construction window cleaning. When standard construction window cleaning techniques are employed to clean the contaminated or defective surfaces on poor quality tempered or heat-strengthened glass, scratching of the glass surface can and very often does result.
Regular annealed glass is tempered or heat-strengthened through a specific heating process in order to provide certain safety characteristics. Prior to the heating process, the glass is sized and belt-sanded to the desired edge finish. If the glass is not then properly washed prior to entering the tempering furnace, and if the furnace rollers upon which the glass rides are not kept clean, microscopic glass fines and chips resulting from the sizing and belt-sanding will become fused to the surface of the heat-treated glass. These small particles will then cause fine scratches on the surface of the glass when standard construction window cleaning procedures are employed.
The glass washer, furnace and general fabricating plant must be kept in proper working order or poor quality products will result. This is a quality issue when fabricating heat-treated glass, not a window cleaning technique issue. Glass scratching, as a result of fabricating debris, has since become a quality, liability and client dissatisfaction issue.
Builders can help resolve this issue by requiring glass and window suppliers to provide only quality heat-treated glass to their projects that can be cleaned using industry standard window cleaning techniques. Builders should only hire qualified construction window cleaners to remove limited amounts of construction debris from their windows.
Protecting windows during construction is always good practice, but will not protect the future owner from a defective glass product when it does require the window cleaner to use a scraper sometime in the future.
Builders should also recognize the difference between fabricating debris scratches and other types of scratches caused by careless plasters, painters, texture crews and untrained workers attempting to re-move construction debris from glass. Fabricating debris scratching is only on heat-treated glass and usually very wide spread, light in nature and mostly visible with direct sunlight.
Fabricating debris is usually invisible, but can sometimes be detected by touch and the gritty sound it makes when a razor blade or scraper is lightly moved over the glass surface. Testing should be done prior to installation. You cannot always detect fabricating debris with these simple tests, but the scratching on the glass it creates is unmistakable. A magnifier can be used to aid in the identification of fabricating debris scratching, with scratches looking like a comet.