This is a direct, well-established material/chemistry incompatibility.
Use a cleaner intended for acid-sensitive natural stone.
Acidic formula; numeric pH not provided.
Professional-strength acidic grout cleaner and brightener.
Do not use Zep Grout Cleaner & Brightener on marble. Zep explicitly lists marble among the surfaces the product is not for, and describes the cleaner as a professional-strength acid-based formula.
Zep describes Grout Cleaner & Brightener as an acid-based grout cleaner and explicitly says it is not for use on marble, terrazzo, travertine, natural stone, chrome, stainless steel, brass or Corian.
Zep — Grout Cleaner & Brightener ↗The Natural Stone Institute explains that marble is calcium-carbonate based and can be etched by acidic solutions. It recommends mild, non-acidic cleaners for calcareous stone.
Natural Stone Institute — Care & Cleaning ↗This is stronger than a generic caution. There is both a direct manufacturer exclusion and a known chemistry/material conflict: an acidic grout cleaner can etch marble and alter its finish.
Rinse the marble thoroughly with clean water and dry it with a soft cloth. If a dull or lighter-looking patch remains, do not try to neutralize or polish it with another household chemical. Acid etching is surface damage rather than ordinary residue, and visible etching may require professional refinishing.
Keep acid grout cleaner off the marble entirely. For marble itself, use a neutral cleaner intended for natural stone. If grout borders marble, choose a grout-cleaning method that the stone manufacturer or stone-care professional confirms is safe for the adjacent marble.
For Marble, the available evidence points against using Zep Grout Cleaner & Brightener. The prohibition or credible damage mechanism described above is stronger than a general-purpose cleaning claim, so a surface-approved alternative is the safer choice.
Evidence scope: exact product. The compatibility record is tied to manufacturer evidence identified for this specific cleaner.
See other cleaners checked for Marble