Hard Water Stain Light vs Medium vs Heavy Decision Tree

Why this matters

Hard water restoration is the single most expensive callback in window cleaning. Misclassify a Stage 3 etch as Stage 1 mineral deposit, treat it with a mild acid, and the customer sees no change after 90 minutes of work that you billed at restoration rates. Worse, polish a non-tempered float that already has surface etch and you can cloud the glass permanently. This tree gives you a hand-on-the-glass test sequence to stage the deposit before you commit to a method, an honest "this won't come off without polishing" gate, and the customer-conversation script for when polishing is needed but the glass is tempered safety glass that you should not polish at all.

Symptom presentation - reading the deposit

Hard water comes off sprinkler overspray, sea spray, evaporative pool splashback, irrigation drift, or a leaky gutter that drops mineral-laden runoff onto a window 100 times per year. Three stages, three field tests:

• Stage 1 - sits on the surface: cloudy haze or droplet ring; rubs partially off with a fingernail; razor blade lifts a flake; vinegar-wet rag clears a window in 90 seconds.
• Stage 2 - bonded to the surface: chalky white that does not move with a fingernail; razor at a low angle scrapes some off but not all; vinegar wet-dwell of 5 minutes only partially clears; specialty restoration product needed.
• Stage 3 - etched into the surface: the deposit IS the glass; the silica has been pitted by minerals; no chemical removes it; only cerium oxide polishing on annealed (non-tempered) float removes it, and polishing tempered glass is a do-not-do.

Quick checks - stage the deposit in 60 seconds

Carry three things in the truck: a single-edge razor blade with a holder, a spray bottle of 1:1 white vinegar to water, and a microfiber cloth.

1. Spray a 4 in test square with vinegar, dwell 60 seconds, wipe firmly with the microfiber. If the square clears to clean glass - Stage 1, full wash will resolve.
2. If the square shows partial improvement (whitish residue remains but reduced), try a razor at 30 deg angle on the cleared patch. If the razor lifts more deposit cleanly without scratching - Stage 2, specialty restoration is needed.
3. If the razor reveals deposit that does not lift but the glass feels rough to a fingernail run sideways across the surface (you'll hear/feel a gritty drag), the glass is etched. Stage 3.
4. Stage 3 confirmation: hold a flashlight at low angle (10 deg from the glass plane) on the dry pane. Etch shows as cloudy patches that move with the light source; surface deposit shows as fixed white that doesn't shift with the light angle.

Isolation tree

1. Does vinegar at 60-second dwell clear the test square completely? Yes → Stage 1. Wash with acidic restoration cleaner (citric acid 5% or oxalic 2%); standard wash time, modest upcharge. No → continue.
2. Does a razor at 30 deg angle lift the residue without grit drag? Yes → Stage 2. Specialty restoration product (commercial bifluoride-free hard-water remover) with 5 to 15 min dwell, white-pad agitation, two passes. No → continue.
3. Does a fingernail dragged sideways feel a gritty surface, or does low-angle flashlight show shifting cloud? Yes → Stage 3 etch. Polishing is the only fix. Determine glass type before quoting. No → re-test in a different area; deposits can vary across one pane.
4. Is the glass tempered (look for the bug stamp in a corner, typically near a sash or hinge)? Yes → DO NOT POLISH. Quote replacement, not restoration. No → continue.
5. Is the glass insulated double-pane and is the etch on the exterior surface only? Yes → polish the exterior surface only with cerium oxide on a low-speed (1500 to 1800 rpm) polisher; never polish over the spacer because the seal is heat-sensitive. No → continue.
6. Is the customer accepting the restoration time and price? Yes → proceed. No → wash to Stage 1 level only, document remaining etch as pre-existing on the work order.

Confirming the diagnosis with the customer

Three lines on the work order before restoration starts:

• "Hard water staging has been tested on a sample area; the deposit is classified as Stage [1/2/3] with the following implications."
• "Stage 3 etched glass cannot be removed chemically; polishing is the only treatment; polishing is not performed on tempered safety glass."
• "Restoration adds [X minutes per pane / restoration is billed as a separate line item]; expected outcome is documented above and verified on the test pane before the customer is invoiced."

For Stage 3 on tempered glass, the only honest conversation is "this glass cannot be restored; replacement is the path forward." Cleaning it harder will not help; polishing it will weaken the tempered surface and may cause it to spontaneously fracture days later. Walk away from polishing tempered.

Confirming diagnosis on a test pane

Always run a Stage 2 or Stage 3 treatment on one sample pane before committing the whole house. Restoration is not refundable labor - you cannot un-polish. Customer signs off on the sample-pane result; if they reject it, you've burned 25 minutes instead of 4 hours.

Remediation by stage

Stage 1 - acidic wash:

• Cleaner: citric acid 5% in water (dish-safe), or commercial product equivalent. Spray, dwell 2 to 5 minutes, agitate with a white pad, squeegee. Rinse the frame after - residual acid pits painted aluminum.
• Frame protection: tape a 2 in poly drape over wood sills; acidic runoff lifts paint on lap-marked exterior trim.

Stage 2 - bonded deposit:

• Cleaner: bifluoride-free commercial hard-water restorer; dwell 5 to 15 minutes per label, agitate with a white pad, neutralize and rinse. NEVER use hydrofluoric acid; it etches the glass you're trying to save and is a serious chemical-burn hazard (OSHA 29 CFR 1910.1200 hazard class).
• Two passes are typical. After the second pass, restage the pane - if it's still Stage 2, you have under-treated; if it's now Stage 3, you have a previously-undetected etch under the deposit.

Stage 3 - polish (annealed only):

• Cerium oxide slurry on a felt or wool pad, 1500 to 1800 rpm, light pressure, constant motion, water-cooled. Stop every 30 seconds to check heat - hot glass shocks and cracks if you spray cold water on it.
• Inspect under low-angle light every pass. Polishing has no overshoot - you keep going until the etch is gone or until you've polished off measurable glass (cerium removes about 0.5 micron per minute under typical pressure).

References

• OSHA 29 CFR 1910.1200, Hazard Communication Standard (SDS, hazard classification, labeling).
• ASTM C1036, Standard Specification for Flat Glass (annealed vs heat-strengthened vs tempered classifications).
• ANSI Z97.1, Safety Glazing Materials Used in Buildings (tempered glass standards and bug-stamp identification).
• IWCA I-14.1, Window Cleaning Safety Standard, hard-water restoration appendix.
• IGMA TM-3000, Glass Handling and Storage Guideline.