· by Michael Blair, Nashville's Window Cleaning
Scratched glass after a window clean is one of the more contentious things that happens in the trade, because the usual cause is a manufacturing defect that only becomes visible when a blade passes over it. Understanding the mechanism explains both why it happens and why the responsibility is genuinely disputed.
Fabricating debris, and why tempered glass is different
Tempered glass is made by heating cut glass and cooling it rapidly on a bed of rollers. Small particles of glass on those rollers can fuse onto the surface of the pane as it passes, leaving hard specks bonded to the glass. This is called fabricating debris and it is invisible in normal light.
A razor scraper run across a pane carrying that debris drags the particles, and each one cuts a line. The scratches appear during cleaning and they were made possible by a defect present since manufacture. Annealed glass, which is not heat treated, generally does not have the problem.
Construction sites and the first clean
The highest risk clean is the first one after construction or renovation, because windows have been exposed to mortar splatter, paint, stucco, drywall compound and concrete dust. Those need aggressive removal, and aggressive removal on tempered glass with debris is exactly the collision described above.
That is why post-construction window cleaning is priced and contracted differently, and why professional cleaners frequently ask for a waiver or an inspection before scraping new tempered glass. It is not a company avoiding responsibility so much as a known industry hazard being acknowledged in advance.
- Tempered panes carry the risk; annealed generally does not
- Post-construction cleans are the highest risk situation
- A scraper should be new, sharp and used wet and flat
- Never scrape dry, and never scrape in a small back-and-forth motion
- Test a small area before scraping a whole pane
How a careful cleaner reduces the risk
By avoiding the blade wherever possible. Most soiling comes off with solution, dwell time and a scrubber, and the scraper is for the residue that will not. A cleaner reaching straight for a blade on every pane is working the way that causes damage.
When a blade is used, it should be new and sharp, used only on wet glass, kept flat to the surface, and pushed in one direction rather than worked back and forth. A dull blade or a dry pane multiplies the risk substantially, and a blade that has picked up grit becomes a cutting tool.
Where responsibility usually lands
It depends on what was known and what was agreed. Where fabricating debris is the cause, the underlying defect is a glass manufacturing issue, and there are documented industry positions to that effect. Where a cleaner scraped dry glass with a dull blade, that is workmanship.
Practically, the way to avoid the argument is to have the conversation before the work: ask whether they scrape tempered glass, what their process is, and what their insurance covers. A company with a clear answer has thought about it; one that has never encountered the question is the greater risk.