Why not use distilled white vinegar like the shower-glass guide?

Vinegar does dissolve minerals, and it also dissolves cement grout. A short, labeled grout cleaner on sound joints is the compromise; a 10–15 minute vinegar soak is how grout turns sandy.

The grout feels sandy after I cleaned it. Did I ruin it?

You have likely etched the cement surface. Stop using acid. Rinse well, let it dry, and plan to seal or regrout. Another pass will make the joints weaker, not whiter.

Guide

How to Remove Hard Water Stains from Grout

Brush the joints with dish soap first — chalky haze is often mixed with soap film. For crust that remains on sound cement grout, use a cleaner labeled for tile and grout mineral deposits, rinse immediately, and stop if the grout feels sandy. Do not copy the vinegar soak used on shower glass.

Grout Hard water buildup

Context

Conditions that change the method

Poor ventilation — Open a window or run the fan before you open a mineral cleaner.
Pet-safe — Keep pets out until the cleaner is rinsed off and the floor is dry.
Delicate surface — Acid cleaners etch marble and limestone and will powder weak grout.

Acids that lift minerals also attack grout

Cement grout is alkaline. Vinegar and other acids dissolve it, which is why a long vinegar soak belongs on glass, not in the joints. Never mix a mineral cleaner or vinegar with bleach or ammonia. If you feel eye, skin, or breathing discomfort, leave the room and get medical advice. Rinse skin or eyes with water while you wait.

What you need

Dish soap and warm water
A nylon grout brush
A cleaner labeled for mineral deposits on tile and grout — read whether it is safe on your grout color and on any stone nearby
A microfiber cloth for rinsing and drying

Ventilate. Decide what you are looking at: a greasy dull film is soap scum; a chalky white crust in the pores is mineral buildup. Many joints are both.
Wash with dish soap and the nylon brush first. Oil sitting on top of the minerals will block any mineral cleaner. If the greasy film was the whole problem, stop here and dry the joints.
If a white crust remains, test a grout-safe mineral cleaner on a short, low joint. Follow the label for dwell time — keep it short. Skip household vinegar soaks.
Brush lightly with the line, then rinse until the cleaner is gone. Acid left in the pores keeps eating cement after you walk away.
Dry the joints. If grout now powders off on your finger, stop. More acid will not repair it — the next step is sealing or regrouting, not another soak.

Why this is not the shower-glass method

Mineral deposits dissolve in acid. So does the cement that holds grout together. Glass can sit in vinegar; grout cannot as a routine. Tile trade guidance is to prefer alkaline or pH-neutral washing, and to treat acids as a short, last-resort pass on sound cement grout — never on marble or crumbling joints.

What to avoid

The 10–15 minute vinegar soak from the shower-glass guide.
Acid on marble, limestone, travertine, or any grout that already feels sandy.
Mixing a mineral cleaner with bleach, ammonia, or leftover soap-scum products.
Leaving cleaner in the joints to “work overnight.”

Products

What to use

Related guides

FAQ

Questions people ask

Why not use distilled white vinegar like the shower-glass guide?: Vinegar does dissolve minerals, and it also dissolves cement grout. A short, labeled grout cleaner on sound joints is the compromise; a 10–15 minute vinegar soak is how grout turns sandy.
The grout feels sandy after I cleaned it. Did I ruin it?: You have likely etched the cement surface. Stop using acid. Rinse well, let it dry, and plan to seal or regrout. Another pass will make the joints weaker, not whiter.

Sources

Cleaning Grout — Tile Council of North America
Learn About the Safer Choice Label — U.S. Environmental Protection Agency