Maintenance and Cleaning of Natural Stone Surfaces
What the exam tests
This domain covers maintenance and cleaning of natural stone surfaces such as marble, travertine, limestone, granite, slate, quartzite and sandstone. Questions focus on identifying stone and finish, choosing pH-compatible chemistry, using safe agitation and rinsing, selecting sealers, and removing stains without etching or scratching.
Core rules
- Identify the stone and finish first. Calcareous stones (marble, travertine, limestone, onyx) are acid-sensitive; siliceous stones (granite, slate, sandstone, quartzite) are generally more acid-resistant but may contain reactive minerals or sensitive finishes.
- Routine cleaning: remove dry soil, pre-spray a neutral-pH stone cleaner, allow dwell time, agitate with a soft brush or microfiber, rinse, and dry. Avoid over-wetting, especially around seams and substrates.
- Never use acidic cleaners, vinegar, citrus, or acidic grout-haze remover on calcareous stone; acid etching dulls polish and cannot be removed by cleaning.
- Strong alkaline or solvent cleaners can strip sealers or dull some finishes; test in an inconspicuous area.
- Distinguish penetrating sealers from topical coatings. Sealer is not a substitute for cleaning, and not all stone requires sealing.
- Use poultices for deep stains; match the poultice liquid to the stain and allow controlled dwell.
Worked example
A honed limestone floor has a pale ring from a lemonade spill and a dark oil spot. Lemonade is acidic, so the ring is likely etching, not soil; do not apply vinegar or acid cleaner. Clean the area with a neutral stone cleaner and soft agitation. For the oil spot, apply an absorbent poultice with a compatible solvent, cover it, allow dwell, remove, rinse and dry. The reasoning: limestone is calcareous and acid-sensitive, while oil needs extraction by poultice rather than stronger scrubbing.
Traps
Assuming all stone is acid-proof; using grout-haze remover on marble; over-wetting; sealing dirty or damp stone; confusing etching with a stain; using aggressive pads on polished surfaces.