Door glass is required by ANSI protocol to be safety. It is usually tempered. As such it usually has defective surfaces that sound like sandpaper when scraped. They have surface inclusions. This is the correct technical name. When a razor blade is used scratches will result.
Now if the IGUs are concave or have negative deflection, your razor blade will not nake adequate contact. Which will force you to bear down on the glass to scrape off whatever needs to be removed. This will just cause you to leave even more scratches.
It is truly amazing how many windows out there share negative deflection and surface inclusions. So many brand new windows have IGUs with these problems. You know that glass and window manufacturers don't care about surface inclusions because they don't cause windows to break or obstruct vision. Seal failure on the other hand does obstruct vision. Not at the very beginning of the problem. But over time. Also negative deflection can cause implosion. Especially when the window is struck by a sharp rock from a lawnmower, or some other means. This can cause a point impact fracture with legs.
Simply put glass should be inspected on a frequent basis. Especially from day one! Which is what the window cleaner does.
Henry Grover Jr.
henrygrover222@gmail.com
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