Terrazzo and Natural Stone: Auto Scrubbing Without Etching or Dulling the Floor

Key takeaways

• Marble, limestone, travertine and cement-matrix terrazzo are calcium based and etch on contact with acids, so use only pH-neutral stone cleaners for routine scrubbing.
• Granite and most slate are silicate stones and tolerate a wider pH range, but their sealers and resin fills often do not.
• Diamond-impregnated maintenance pads let an auto scrubber hold or build shine on stone with water and neutral cleaner, no coating required.
• Rinse and recover thoroughly, because residue on polished stone dulls the finish and raises slip risk.
• Identify the stone before choosing a chemical, since one wrong product can etch a whole lobby in a single pass.

Terrazzo and natural stone are safely auto scrubbed with a pH-neutral stone cleaner, a soft pad or diamond-impregnated maintenance pad, light to medium down pressure, and low solution flow with thorough water pickup. The single biggest risk is chemistry: marble, limestone, travertine and most terrazzo contain calcium carbonate, and any acidic cleaner will etch them, leaving dull marks that only re-honing can remove.

Unlike vinyl or sealed concrete, stone often has no sacrificial coating, so whatever the pad and chemical do, they do to the floor itself.

Step one: identify the stone before you scrub

"Marble" or "stone" is not enough of a label. Use this field checklist before choosing chemicals or pads.

1. Check building records or ask the facility. Original specs usually name the stone or terrazzo system (cement-matrix or epoxy-matrix).
2. Look at the surface. Terrazzo shows chips set in a matrix with divider strips. Marble shows veining. Granite shows interlocking speckled crystals. Slate is layered, often with a cleft texture. Limestone is uniform and fine grained, sometimes with fossil fragments.
3. Check the finish. Polished (mirror reflection), honed (matte, smooth) or textured (flamed, cleft, tumbled). Polished calcium stone shows etching most clearly.
4. Check for a topical coating. Rub a white pad with a little neutral cleaner in a corner. If a cloudy film or residue comes up, there is a coating or old sealer on top. Many older terrazzo floors were maintained with topical sealers and finishes.
5. Do a careful acid sensitivity check only if still unsure. A drop of a mild acid such as vinegar on a hidden spot will fizz or leave a dull mark on calcium-based stone. This test itself etches, so only do it in a closet corner or under equipment, and wipe and rinse immediately.

If you still cannot tell, treat the floor as acid-sensitive: neutral chemistry on granite costs nothing, acid on marble costs a restoration visit.

How the common stones behave

Epoxy terrazzo, now common in airports and schools, is more chemically tolerant than cement-matrix terrazzo, but its marble chips still etch.

Chemical pH guidance

• Routine scrubbing, all stone: neutral stone cleaner, pH about 7 to 8.5. Many are labeled specifically for stone and terrazzo. Avoid general-purpose cleaners that contain acids, citrus extracts or vinegar.
• Heavy soil on granite or slate: mild alkaline cleaner, pH about 9 to 10, followed by a clear water rinse. Check that it is safe for the sealer.
• Deep cleaning terrazzo or marble: a stone-safe alkaline cleaner can be used periodically, but high-pH strippers (pH 12 and up) can dull some polished stone and attack epoxy matrix over repeated use. Use the mildest product that works.
• Never on calcium stone: acid descalers, rust removers, many restroom bowl and urinal cleaners, and products with phosphoric, hydrochloric, sulfamic or citric acid. Restroom overspray causes many etched patches.

Dosing matters as much as pH. Stone has fine pores, and leftover surfactant residue dulls polished stone and makes it slick. If you use a chemical dosing system, set it at or below the label dilution.

Pads, brushes and diamond pads

The pad selector treats stone conservatively, and so should you.

What diamond pads are. Diamond maintenance pads are floor pads impregnated with industrial diamond abrasive at a range of grits. Coarser grits (commonly a few hundred) are used by restoration contractors to hone. Finer grits (often 800 to 3,000 and higher) are used during routine scrubbing to keep the surface refined and reflective, without applying a coating. Many terrazzo and marble floors in airports and hospitality are now maintained this way, which is similar to how polished concrete is kept up. Grit labeling varies by maker.

Disc scrubbers are the typical machine for stone, because pads drive flat across a polished surface. Orbital scrubbers are also a good match on stone, with gentle, even contact; see orbital vs rotary for the trade-offs. Background on bristle and pad types is in brushes and pads.

Settings for stone floors

• Down pressure: light to medium. Heavy pressure plus an aggressive pad scratches. With diamond pads, follow the maker's guidance; most are designed for normal scrubber pressure.
• Solution flow: low to medium. Stone needs enough water for the pad to glide and soil to suspend, but standing water on porous limestone or travertine can cause dark water marks, and water sitting in terrazzo divider strip joints is a slip and staining risk.
• Vacuum and squeegee: recovery must be complete. Check the squeegee blade edge before scrubbing a polished lobby; a nicked blade leaves a trail that dries into a visible line on dark stone. See squeegees.
• Speed: normal walk-behind pace, about 150 to 200 ft/min.

Worked example: diamond pad versus topical coating maintenance

A hotel lobby has 4,000 sq ft (about 372 m2) of polished terrazzo. Two maintenance approaches, using our estimate of typical labor:

• Coating approach: daily scrub with red pad plus periodic burnishing, then strip and recoat once or twice a year. Strip and recoat often runs a few hundred sq ft per hour including drying, so it can take one or two overnight shifts plus a closure.
• Diamond approach: daily scrub with a fine diamond pad and neutral cleaner, swapping to a finer grit weekly. No strip and recoat. Diamond pads cost more but typically last many sessions.

Scrubber Guide model: if a 20 in walk-behind scrubs the lobby at about 11,400 sq ft/hr (20 / 12 x 175 x 60 x 0.65), the daily scrub is about 21 minutes either way. The difference is the closures. Removing one or two strip-and-recoat events per year saves those shifts and avoids closing the lobby. Plug in local labor and pad prices; the total cost of ownership page shows how to weigh consumables against labor.

Sealers on stone

There are two very different products called "sealers":

• Penetrating (impregnating) sealers soak into the stone and reduce absorption of oil and water. They do not change appearance much and do not create a film. They do not prevent etching, because acid still reaches the stone surface. Typical reapplication intervals are 1 to 3 years in commercial traffic, guided by a simple water-drop test: if water darkens the stone within a few minutes, reseal.
• Topical sealers and coatings form a film on top. They protect against etching while intact but scratch, wear in traffic lanes, and must be stripped. Strippers are high pH, which is hard on some stone. Many restoration specialists now prefer penetrating sealers plus diamond maintenance.

Before switching to diamond maintenance, have any existing coating fully removed, or the pads will smear it into haze.

Mistakes that ruin stone floors

• Using an all-purpose or restroom acid cleaner in the solution tank. One tank can etch a whole corridor.
• Running black stripping pads or grit brushes on polished marble to "get it really clean".
• Overdosing neutral cleaner until a dull, slippery film builds up.
• Skipping the dust mop, so sand under the pad scratches the polish.
• Coating stone not designed for it, then stripping it harshly every year.

Routine schedule by traffic level

Entrance matting matters most on stone, because tracked-in sand dulls it. For guest-facing spaces, see hotels and hospitality.

Frequently asked questions