Quartz is not identified among the approved surfaces, and this is a professional-strength acidic grout cleaner. Acid may damage or dull quartz surfaces, especially polished or resin-bound finishes.
Why
Zep specifically approves grout, not quartz countertops or slabs. The product’s acidic chemistry creates a plausible damage mechanism, and the evidence does not establish compatibility with quartz.
What to do
Do not use on quartz. Use only on the intended grout areas, keeping it off adjacent quartz; test an inconspicuous area and rinse thoroughly as directed.
pH
Acidic formula; numeric pH not provided.
Relevant chemistry
Professional-strength acidic grout cleaner and brightener.
Source: official product page ↗