The short answer
Fresh mineral deposits come off with cleaning. Once they bond and etch the glass, cleaning cannot remove them. At that point the glass needs restoration, and if the etching is deep enough, replacement.
Where the minerals come from
- Irrigation overspray hitting the glass
- Rain runoff from precast concrete and masonry
- Acid rain and pollution
- Oxidation from metal window frames
How to tell what stage you are in
| What you see | What it usually means | What fixes it |
|---|---|---|
| Spots that come off with cleaning | Surface deposits | Routine cleaning, on a tighter cadence |
| Spots in a sprinkler pattern that cleaning will not lift | Minerals bonding to the glass | Hard-water removal, then fix the source |
| A haze that never clears | Etching | Glass restoration |
| Dull, pitted frames | Metal oxidation | Metal restoration |
What restoration involves
- Removing hard-water and mineral stains that have etched the glass
- Sanding, buffing and polishing out scratches
- Treatments that help prevent future staining
Restoration costs more per pane than routine cleaning. Replacement is the cliff after it: thousands per opening, and possibly permits, scaffolding and tenant disruption. See glass and metal restoration and the facade, glass and metal restoration guide.
How to stop it coming back
- Fix the source. Adjust sprinklers so they stop hitting the glass.
- Tighten the cadence on exposed elevations so deposits never bond.
- Add hard-water removal to the scope where overspray cannot be fully stopped.
- Ask about protective treatments after restoration.
Get an honest assessment
S&K will look at the glass and tell you whether it needs cleaning or restoration, then build a program that keeps it from getting there again. More on the economics in the hidden cost of neglected commercial glass.
