Sealed Concrete: How to Auto Scrub Acrylic, Penetrating and Urethane Sealed Floors

Key takeaways

• Identify the sealer first, because acrylic, penetrating and urethane sealers tolerate very different pads and chemicals.
• A neutral cleaner in the pH 7 to 9 range with a red pad or soft polypropylene brush handles most daily soil on film-forming sealers.
• Penetrating-sealed concrete behaves like bare concrete and can take blue or green pads and alkaline degreasers, but never acids.
• Most sealed-floor damage comes from too much down pressure, strong degreasers left to dwell, and grit brushes on thin acrylic films.

To scrub sealed concrete with an auto scrubber, use a neutral cleaner (pH 7 to 9), a red pad or soft polypropylene brush, low to medium down pressure and a low solution flow, then let the squeegee pick up everything in one pass. It is safe on almost every sealer. Go more aggressive only after you know which sealer is on the floor, because the right answer for a penetrating sealer will strip an acrylic one.

The three sealer families and why they matter

A film-forming sealer sits on top of the concrete as a thin coating. A penetrating sealer soaks into the pores and reacts below the surface, leaving no film to wear off. The difference decides how hard you can scrub.

Acrylic is common in light commercial and decorative concrete because it is cheap and easy to recoat, and it is the most fragile under a scrubber. Penetrating sealers dominate in warehouses and parking structures, where forklifts and tires would wear a film off within months. Urethane shows up where an owner wanted gloss plus durability.

Field checklist: identify the sealer before the first pass

If the facility has no product data sheet on file, run this check on a low-traffic spot such as behind a door or under a rack. It takes about ten minutes.

1. Water drop test. Put a few drops of water on a clean, dry spot. Beading with no darkening means there is a sealer present. Beading on a floor with no visible sheen points to a penetrating silane or siloxane.
2. Sheen test. Look at the floor at a low angle toward a light source. A uniform film with a visible edge at walls or around drains is a film former. Gloss with no film edge and a "stone" look may be densified or polished concrete instead (see polished concrete).
3. Fingernail or coin scratch. On a hidden spot, a soft film that marks easily is usually acrylic. A hard film that resists marking is more likely urethane or epoxy.
4. Solvent rub. Wipe a hidden spot with a rag dampened in xylene or a similar strong solvent for about 30 seconds. Acrylic turns tacky or softens. Urethane and epoxy do not react quickly. Wear gloves, ventilate, and do this only where solvent use is permitted.
5. Pad edge test. Run a red pad by hand over a square foot with neutral cleaner. If the water turns milky white, you are removing acrylic or a floor finish and should drop to a white pad or softer brush.
6. Record it. Log the sealer type and result so every operator uses the same settings.

If the floor turns out to be a thick, colored, glossy coating rather than a thin sealer, it is probably an epoxy or urethane resin system. Those have their own rules on our epoxy floors page.

Pads and brushes by sealer

Pad colors follow the common 3M-style convention, which varies a little by maker. Our pad selector narrows the choice further by soil type.

Brushes suit broom-finished or shot-blasted concrete because bristles reach texture a flat pad bridges over; on smooth troweled slabs a pad gives more even contact. See brush vs pad.

Chemical pH guidance

• Acrylic: Stay at pH 7 to 9 for routine work. Alkaline degreasers above roughly pH 10 to 11 soften acrylic, and repeated use dulls it or strips it in the wheel paths. Never use solvent-based degreasers.
• Penetrating: The sealer is inside the concrete, so alkaline cleaners up to about pH 11 to 12 are fine for oil and rubber marks. Rinse or double scrub so alkaline residue does not bloom white as it dries.
• Urethane: pH 7 to 10 is a comfortable working range. Short contact with a stronger degreaser is usually fine, but do not let it sit and dry.
• All sealed concrete: Avoid acidic cleaners (below roughly pH 5) for routine use. Acid attacks the cement paste, and on a penetrating sealer there is no film to protect it. Rust and efflorescence removal is a spot job with a product made for it, followed by a thorough rinse.

Over-concentration is the most common chemical mistake. Operators "add a little extra" and the residue left behind makes the floor sticky, attracts soil and creates the streaking described in streaks and water trails. If the dilution says 2 oz per gallon, a 20 gallon tank gets 40 oz, measured, not glugged.

Settings: down pressure and solution flow

Down pressure is the force pushing the pad onto the floor. More is not better on film-forming sealers, because it converts cleaning action into abrasion. See down pressure for how the numbers are rated.

Flow numbers are typical for mid-size walk-behinds and scale up for ride-on machines. Use only enough solution to keep the pad wet; flooding just leaves water the squeegee cannot collect at the edges.

Worked example: double scrubbing a sealed garage

Garages and loading areas often need a double scrub: a first pass with the squeegee up to lay down solution and let it dwell, then a second pass to scrub and recover. Here is a Scrubber Guide model for a 12,000 sq ft (about 1,115 m2) sealed parking level with a penetrating sealer.

Assumptions: 28 in walk-behind, 175 ft/min, efficiency 0.65, solution flow 0.6 gal/min on the first pass and 0.4 gal/min on the second, 25 gallon solution tank.

• Productivity per pass: 28 / 12 x 175 x 60 x 0.65 = about 15,900 sq ft/hr.
• Time per pass: 12,000 / 15,900 = about 0.75 hr, so roughly 1.5 hours for both passes plus dwell time of 5 to 10 minutes.
• Solution use: (0.6 x 45 min) + (0.4 x 45 min) = 27 + 18 = 45 gallons.
• Tank fills: 45 / 25 = 1.8, so plan two fills and one recovery dump at minimum.

The same floor single-scrubbed at 0.4 gal/min uses about 18 gallons. That is why double scrubbing is a weekly or as-needed task, not a nightly one. You can check your own numbers in the productivity calculator.

Mistakes that damage sealed concrete

• Grit brushes on acrylic. Abrasive bristles cut through a thin acrylic film in a few passes and leave a dull wheel path pattern.
• Parking the machine with the pad down. A spinning or even stationary wet pad on one spot can burn a ring into acrylic and urethane.
• Strong degreasers on acrylic. A pH 12 degreaser that works great on a penetrating-sealed warehouse will soften an acrylic showroom floor.
• Acid "brighteners." Acid cleaners etch the surface paste and can leave a chalky, uneven look that no scrubbing fixes.
• Scrubbing over grit. Sand and road salt under the pad act like sandpaper. Sweep or dust mop first, especially in garages after winter.
• Ignoring the recoat signal. An acrylic sealer that has worn through in traffic lanes will not look better with more scrubbing. It needs a recoat.

Routine schedule by traffic level

For large warehouses, the warehouses and distribution guide covers sweeping first, aisle sequencing and when a sweeper-scrubber is worth it.

Frequently asked questions